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UNITED STATES
SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

FORM 10-K

ý ANNUAL REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934
For the Fiscal Year Ended December 31, 2007
OR
o TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934
For the transition period from                to                

Commission File No. 0-26456

ARCH CAPITAL GROUP LTD.

(Exact name of registrant as specified in its charter)

Bermuda
(State or other jurisdiction of
incorporation or organization)		   Not applicable
(I.R.S. Employer
Identification No.)

Wessex House, 45 Reid Street
Hamilton HM 12, Bermuda
(Address of principal executive offices)
 
(441) 278-9250
(Registrant's telephone number, including area code)

         Securities registered pursuant to Section 12(b) of the Exchange Act:

Title of Each Class
   Name of each Exchange on which Registered
Common Shares, $0.01 par value per share
8.000% Non-Cumulative Preferred Shares, Series A, $0.01 par value per share
7.875% Non-Cumulative Preferred Shares, Series B, $0.01 par value per share		   NASDAQ Stock Market (Common Shares)
New York Stock Exchange

         Securities registered pursuant to Section 12(g) of the Exchange Act: None

         Indicate by check mark if the registrant is a well-known seasoned issuer, as defined in Rule 405 of the Securities Act. Yes ý    No o

         Indicate by check mark if the registrant is not required to file reports pursuant to Section 13 or Section 15(d) of the Exchange Act. Yes o    No ý

         Indicate by check mark whether the registrant (1) has filed all reports required to be filed by Section 13 or 15(d) of the Exchange Act during the preceding 12 months (or for such shorter period that the registrant was required to file such reports), and (2) has been subject to such filing requirements for the past 90 days. Yes ý    No o

         Indicate by check mark if disclosure of delinquent filers pursuant to Item 405 of Regulation S-K is not contained herein, and will not be contained, to the best of registrant's knowledge, in definitive proxy or information statements incorporated by reference in Part III of this Form 10-K or any amendment to this Form 10-K. ý

         Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, or a smaller reporting company. See the definitions of "large accelerated filer," "accelerated filer" and "smaller reporting company" in Rule 12b-2 of the Exchange Act. (Check one):

Large accelerated filer ý   Accelerated filer o   Non-accelerated filer o
 (Do not check if a smaller reporting company)		   Smaller reporting company o

         Indicate by check mark whether the registrant is a shell company (as defined in Rule 12b-2 of the Exchange Act). Yes o    No ý

         The aggregate market value of the voting and non-voting common equity held by non-affiliates, computed by reference to the closing price as reported by the NASDAQ Stock Market as of the last business day of the Registrant's most recently completed second fiscal quarter, was approximately $4.29 billion.

         As of February 22, 2008, there were 65,300,062 of the registrant's common shares outstanding.


DOCUMENTS INCORPORATED BY REFERENCE

         Portions of Part III and Part IV incorporate by reference our definitive proxy statement for the 2008 annual meeting of shareholders to be filed with the Securities and Exchange Commission pursuant to Regulation 14A before April 30, 2008.


ARCH CAPITAL GROUP LTD.

TABLE OF CONTENTS

Item
    
   Page
PART I

ITEM 1.
 
BUSINESS
 
1
ITEM 1A.   RISK FACTORS   38
ITEM 1B.   UNRESOLVED STAFF COMMENTS   60
ITEM 2.   PROPERTIES   60
ITEM 3.   LEGAL PROCEEDINGS   61
ITEM 4.   SUBMISSION OF MATTERS TO A VOTE OF SECURITY HOLDERS   61

PART II

ITEM 5.
 
MARKET FOR REGISTRANT'S COMMON EQUITY, RELATED STOCKHOLDER MATTERS AND ISSUER PURCHASES OF EQUITY SECURITIES
 
62
ITEM 6.   SELECTED FINANCIAL DATA   65
ITEM 7.   MANAGEMENT'S DISCUSSION AND ANALYSIS OF FINANCIAL CONDITION AND RESULTS OF OPERATIONS.    67
ITEM 7A.   QUANTITATIVE AND QUALITATIVE DISCLOSURES ABOUT MARKET RISK   114
ITEM 8.   FINANCIAL STATEMENTS AND SUPPLEMENTARY DATA   114
ITEM 9.   CHANGES IN AND DISAGREEMENTS WITH ACCOUNTANTS ON ACCOUNTING AND FINANCIAL DISCLOSURE   114
ITEM 9A.   CONTROLS AND PROCEDURES   114
ITEM 9B.   OTHER INFORMATION   115

PART III

ITEM 10. 
 
DIRECTORS, EXECUTIVE OFFICERS AND CORPORATE GOVERNANCE
 
116
ITEM 11.   EXECUTIVE COMPENSATION   116
ITEM 12.   SECURITY OWNERSHIP OF CERTAIN BENEFICIAL OWNERS AND MANAGEMENT AND RELATED STOCKHOLDER MATTERS   116
ITEM 13.   CERTAIN RELATIONSHIPS AND RELATED TRANSACTIONS, AND DIRECTOR INDEPENDENCE   117
ITEM 14.   PRINCIPAL ACCOUNTANT FEES AND SERVICES   117

PART IV

ITEM 15.
 
EXHIBITS AND FINANCIAL STATEMENT SCHEDULES
 
117

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CAUTIONARY NOTE REGARDING FORWARD-LOOKING STATEMENTS

        The Private Securities Litigation Reform Act of 1995 ("PLSRA") provides a "safe harbor" for forward-looking statements. This report or any other written or oral statements made by or on behalf of us may include forward-looking statements, which reflect our current views with respect to future events and financial performance. All statements other than statements of historical fact included in or incorporated by reference in this report are forward-looking statements. Forward-looking statements, for purposes of the PLSRA or otherwise, can generally be identified by the use of forward-looking terminology such as "may," "will," "expect," "intend," "estimate," "anticipate," "believe" or "continue" and similar statements of a future or forward-looking nature or their negative or variations or similar terminology.

        Forward-looking statements involve our current assessment of risks and uncertainties. Actual events and results may differ materially from those expressed or implied in these statements. Important factors that could cause actual events or results to differ materially from those indicated in such statements are discussed below, elsewhere in this report and in our periodic reports filed with the Securities and Exchange Commission ("SEC"), and include:

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        In addition, other general factors could affect our results, including developments in the world's financial and capital markets and our access to such markets.

        All subsequent written and oral forward-looking statements attributable to us or persons acting on our behalf are expressly qualified in their entirety by these cautionary statements. The foregoing review of important factors should not be construed as exhaustive and should be read in conjunction with other cautionary statements that are included herein or elsewhere. We undertake no obligation to publicly update or revise any forward-looking statement, whether as a result of new information, future events or otherwise.

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PART I

ITEM 1.    BUSINESS

        We refer you to Item 1A "Risk Factors" for a discussion of risk factors relating to our business.


OUR COMPANY

General

        Arch Capital Group Ltd. ("ACGL" and, together with its subsidiaries, the "Company," "we," or "us") is a Bermuda public limited liability company with approximately $4.34 billion in capital at December 31, 2007 and, through operations in Bermuda, the United States, Europe and Canada, writes insurance and reinsurance on a worldwide basis. While we are positioned to provide a full range of property and casualty insurance and reinsurance lines, we focus on writing specialty lines of insurance and reinsurance.

        We launched an underwriting initiative in October 2001 to meet current and future demand in the global insurance and reinsurance markets. Since that time, we have attracted a proven management team with extensive industry experience and enhanced our existing global underwriting platform for our insurance and reinsurance businesses. It is our belief that our underwriting platform, our experienced management team and our strong capital base that is unencumbered by significant pre-2002 risks have enabled us to establish a strong presence in the insurance and reinsurance markets. For 2007, our sixth full year of operation, we wrote $2.9 billion of net premiums, reported net income available to common shareholders of $832.1 million and earned a return on average equity of 23.9%. Diluted book value per share increased by 25.4% to $55.12 at December 31, 2007 from $43.97 per share at December 31, 2006.

        Since late 2001, we have raised additional capital in support of the underwriting activities of our insurance and reinsurance operations. In October 2001, the commencement of our underwriting initiatives included an equity capital infusion of $763.2 million led by funds affiliated with Warburg Pincus LLC ("Warburg Pincus funds") and Hellman & Friedman LLC ("Hellman & Friedman funds"). In April 2002, we completed a public offering of 7,475,000 of our common shares and received net proceeds of $179.2 million and, in September 2002, we received net proceeds of $74.3 million from the exercise of class A warrants by our principal shareholders and other investors. In March 2004, we completed a public offering of 4,688,750 of our common shares and received net proceeds of $179.3 million. In May 2004, we completed the public offering of $300 million principal amount of our 7.35% senior notes due May 2034 and received net proceeds of $296.4 million, of which $200 million of the net proceeds was used to repay all amounts outstanding under our existing credit facility. In February 2006, we issued in a public offering $200.0 million of our 8.00% series A non-cumulative preferred shares with a liquidation preference of $25.00 per share and received net proceeds of $193.5 million. In May 2006, we issued in a public offering $125.0 million of our 7.875% series B non-cumulative preferred shares with a liquidation preference of $25.00 per share and received net proceeds of $120.9 million. The net proceeds of the offerings were used to support the underwriting activities of our insurance and reinsurance subsidiaries.

        In February 2007, our board of directors authorized us to invest up to $1 billion in ACGL's common shares through a share repurchase program. Repurchases under the program may be effected from time to time in open market or privately negotiated transactions through February 2009. During 2007, we repurchased approximately 7.8 million common shares for an aggregate purchase price of $537.1 million. As a result of share repurchase transactions in 2007, book value per common share at December 31, 2007 was reduced by $1.45 per share and weighted average shares outstanding were reduced by 3.3 million. The timing and amount of the repurchase transactions under this program will depend on a variety of factors, including market conditions and corporate and regulatory considerations. In connection with the repurchase program, the Warburg Pincus funds and Hellman &

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Friedman funds waived their rights relating to share repurchases under their shareholders agreement with ACGL for all repurchases of common shares by ACGL under the repurchase program in open market transactions and certain privately negotiated transactions. In May 2007, the Hellman & Friedman funds ceased to own shares of ACGL and their rights under the shareholders agreement with ACGL terminated.

        ACGL's registered office is located at Clarendon House, 2 Church Street, Hamilton HM 11, Bermuda (telephone number: (441) 295-1422), and its principal executive offices are located at Wessex House, 45 Reid Street, Hamilton HM 12, Bermuda (telephone number: (441) 278-9250). ACGL makes available free of charge through its website, located at http://www.archcapgroup.bm, its annual reports on Form 10-K, quarterly reports on Form 10-Q, current reports on Form 8-K, and all amendments to those reports as soon as reasonably practicable after such material is electronically filed with, or furnished to, the SEC. The public may read and copy any materials ACGL files with the SEC at the SEC's Public Reference Room at 450 Fifth Street, NW, Washington, D.C. 20549. The public may obtain information on the operation of the Public Reference Room by calling 1-800-SEC-0330. The SEC also maintains an Internet site that contains reports, proxy and information statements, and other information regarding issuers that file electronically with the SEC (such as ACGL) and the address of that site is http://www.sec.gov.

Our History

        ACGL was formed in September 2000 and became the sole shareholder of Arch Capital Group (U.S.) Inc. ("Arch-U.S.") pursuant to an internal reorganization transaction completed in November 2000, as described below. Arch-U.S. is a Delaware company formed in March 1995 under the original name of "Risk Capital Holdings, Inc.," which commenced operations in September 1995 following the completion of an initial public offering. From that time until May 2000, Arch-U.S. provided reinsurance and other forms of capital for insurance companies through its wholly owned subsidiary, Arch Reinsurance Company ("Arch Re U.S."), a Nebraska corporation formed in 1995 under the original name of "Risk Capital Reinsurance Company."

        On May 5, 2000, Arch-U.S. sold the prior reinsurance operations of Arch Re U.S. to Folksamerica Reinsurance Company ("Folksamerica") in an asset sale, but retained its surplus and U.S.-licensed reinsurance platform. The sale was precipitated by, among other things, losses on the reinsurance business of Arch Re U.S. and increasing competition, which had been adversely affecting the results of operations and financial condition of Arch Re U.S. The Folksamerica transaction, which resulted from extensive arm's length negotiation, was structured as a transfer and assumption agreement (and not as reinsurance) and, accordingly, the loss reserves (and any related reinsurance recoverables) related to the transferred business are not included in the balance sheet of Arch Re U.S. However, in the event that Folksamerica refuses or is unable to make payment of claims on the reinsurance business assumed by it in the May 2000 sale and the notice given to reinsureds is found not to be an effective release by such reinsureds, Arch Re U.S. would be liable for such claims. In addition, Arch Re U.S. retained all liabilities not assumed by Folksamerica, including all liabilities not arising under reinsurance agreements transferred to Folksamerica in the asset sale. On November 8, 2000, following the approval by Arch-U.S.'s shareholders, Arch-U.S. completed an internal reorganization that resulted in Arch-U.S. becoming a wholly owned subsidiary of ACGL.

        During the period from May 2000 through the announcement of our underwriting initiative in October 2001, we built and acquired insurance businesses that were intended to enable us to generate both fee-based revenue (e.g., commissions and advisory and management fees) and risk-based revenue (i.e., insurance premium). As part of this strategy, we built an underwriting platform that was intended to enable us to maximize risk-based revenue during periods in the underwriting cycle when we believed it was more favorable to assume underwriting risk. In October 2001, we concluded that underwriting

2


conditions favored dedicating our attention exclusively to building our insurance and reinsurance business.

        The development of our underwriting platform included the following steps: (1) after the completion of the Folksamerica asset sale, we retained our U.S.-licensed reinsurer, Arch Re U.S., and Arch Excess & Surplus Insurance Company ("Arch E&S"), currently an approved excess and surplus lines insurer in 46 states and the District of Columbia and an admitted insurer in one state; (2) in May 2001, we formed Arch Reinsurance Ltd. ("Arch Re Bermuda"), our Bermuda-based reinsurance and insurance subsidiary; (3) in June 2001, we acquired Arch Risk Transfer Services Ltd., which included Arch Insurance Company ("Arch Insurance"), currently an admitted insurer in 50 states, the District of Columbia, Puerto Rico and the U.S. Virgin Islands with a branch office in Canada, and rent-a-captive and other facilities that provide insurance and alternative risk transfer services; (4) in February 2002, we acquired Arch Specialty Insurance Company ("Arch Specialty"), currently an approved excess and surplus lines insurer in 49 states, the District of Columbia, Puerto Rico and the U.S. Virgin Islands and an admitted insurer in one state; (5) in June 2003, we acquired Western Diversified Casualty Insurance Company ("Western Diversified"), an admitted insurer in 48 states and the District of Columbia; (6) in May 2004, our London-based subsidiary, Arch Insurance Company (Europe) Limited ("Arch-Europe"), was approved by the Financial Services Authority in the U.K. to commence insurance underwriting activities and began writing a range of specialty commercial lines in Europe and the U.K. during the 2004 third quarter; (7) in January 2005, Arch Insurance received its federal license to commence underwriting in Canada and began writing business in the first quarter of 2005; and (8) in November 2006, Arch Reinsurance Ltd., Hamilton (Bermuda), European Branch Zurich ("Arch Re Swiss Branch"), the Swiss branch of Arch Re Bermuda, was registered with the commercial register of the Canton of Zurich to commence reinsurance underwriting activities in Switzerland. All liabilities arising out of the business of Arch Specialty and Western Diversified prior to the closing of our acquisitions of such companies were reinsured and guaranteed by the respective sellers, Sentry Insurance a Mutual Company ("Sentry") and Protective Life Corporation and certain of its affiliates.

        In 2007, we expanded our underwriting platform by (i) forming Arch Re Accident & Health ApS ("Arch Re Denmark"), a Danish underwriting agency which conducts accident and health underwriting as a branch office of Arch-Europe; (ii) acquiring the assets of Wexford Underwriting Managers, Inc. ("Wexford"), a managing general agent, to write excess workers' compensation and employers' liability insurance, a new line of business for us; and (iii) launching our property facultative reinsurance underwriting operations based in Farmington, Connecticut. On January 22, 2008, Arch Re Bermuda and Gulf Investment Corporation GSC ("GIC") entered into a joint venture agreement for the purpose of forming a reinsurance company in the Dubai International Financial Centre. GIC is owned equally by the six member states of the Gulf Cooperation Council ("GCC"), which include Bahrain, Kuwait, Oman, Qatar, Saudi Arabia and the United Arab Emirates. The new company will provide property and casualty reinsurance primarily in those member states of the GCC.

Operations

        We classify our businesses into two underwriting segments, insurance and reinsurance. For an analysis of our underwriting results by segment, see note 3, "Segment Information," of the notes accompanying our consolidated financial statements and "Management's Discussion and Analysis of Financial Condition and Results of Operations."

        Our insurance operations are conducted in Bermuda, the United States, Europe and Canada. Our insurance operations in Bermuda are conducted through Arch Insurance (Bermuda), a division of Arch Re Bermuda, which has an office in Hamilton, Bermuda. In the U.S., our insurance group's principal insurance subsidiaries are Arch Insurance, Arch E&S and Arch Specialty. The headquarters for our

3

insurance group's U.S. operations is located in New York City. The insurance group has additional offices throughout the U.S., including four regional offices located in: Alpharetta, Georgia; Chicago, Illinois; New York, New York; and San Francisco, California. Arch Insurance has a branch office in Toronto, Canada, which began writing business in the first quarter of 2005. Our insurance group's European operations are conducted through Arch-Europe, based in London, which became operational during the 2004 third quarter. Arch-Europe also has branches in Germany, Italy and Spain. Arch Re Denmark is also a branch of Arch-Europe which underwrites on behalf of Arch-Europe, although it is part of our reinsurance operations more fully described in "Our Reinsurance Operations". As of February 15, 2008, our insurance group had approximately 1,020 employees.

        Strategy.    Our insurance group's strategy is to operate in lines of business in which underwriting expertise can make a meaningful difference in operating results. It focuses on talent rather than labor intensive business and seeks to operate profitably (on both a gross and net basis) across all of its product lines. To achieve these objectives, our insurance group's operating principles are to:

        Our insurance group writes business on both an admitted and non-admitted basis. Our insurance group focuses on the following areas:

4

        Underwriting Philosophy.    Our insurance group's underwriting philosophy is to generate an underwriting profit (on both a gross and net basis) through prudent risk selection and proper pricing across all types of business. One key to this philosophy is the adherence to uniform underwriting standards across each product line that focuses on the following:

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        Premiums Written and Geographic Distribution.    Set forth below is summary information regarding net premiums written for our insurance group:

 
   Years Ended December 31,
 
   2007
   2006
   2005
(U.S. dollars in thousands)

   Amount
   % of
Total
   Amount
   % of
Total
   Amount
   % of
Total
  Net premiums written                              
  Property, marine and aviation   $ 330,460   19.3   $ 320,928   19.4   $ 228,642   15.4
  Professional liability(1)     328,369   19.1     289,328   17.5     227,828   15.4
  Construction, surety and national accounts     283,997   16.5     274,460   16.6     233,133   15.7
  Programs     235,793   13.7     225,653   13.7     232,156   15.7
  Executive assurance     185,351   10.8     193,694   11.8     169,430   11.4
  Casualty     181,774   10.6     220,244   13.3     271,788   18.4
  Healthcare     63,757   3.7     68,026   4.1     70,928   4.8
  Other(2)     108,047   6.3     59,723   3.6     47,395   3.2
   
 
 
 
 
 
  Total   $ 1,717,548   100.0   $ 1,652,056   100.0   $ 1,481,300   100.0
   
 
 
 
 
 
 
Net premiums written by client location
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
  United States   $ 1,323,376   77.1   $ 1,340,792   81.2   $ 1,293,938   87.4
  Europe     250,824   14.6     182,815   11.0     107,283   7.2
  Other     143,348   8.3     128,449   7.8     80,079   5.4
   
 
 
 
 
 
  Total   $ 1,717,548   100.0   $ 1,652,056   100.0   $ 1,481,300   100.0
   
 
 
 
 
 
 
Net premiums written by underwriting location
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
  United States   $ 1,309,401   76.2   $ 1,297,974   78.6   $ 1,258,162   84.9
  Europe     330,746   19.3     269,128   16.3     174,676   11.8
  Other     77,401   4.5     84,954   5.1     48,462   3.3
   
 
 
 
 
 
  Total   $ 1,717,548   100.0   $ 1,652,056   100.0   $ 1,481,300   100.0
   
 
 
 
 
 
(1)
Includes travel and accident business.

(2)
Includes excess workers' compensation and employers' liability business.

        Marketing.    Our insurance group's products are marketed principally through a group of licensed independent retail and wholesale brokers. Clients (insureds) are referred to our insurance group through a large number of international, national and regional brokers and captive managers who receive from the insured or insurer a set fee or brokerage commission usually equal to a percentage of gross premiums. In the past, our insurance group also entered into contingent commission arrangements with some brokers that provide for the payment of additional commissions based on volume or profitability of business. In general, our insurance group has no implied or explicit commitments to accept business from any particular broker and, neither brokers nor any other third party has the authority to bind our insurance group, except in the case where underwriting authority may be delegated contractually to selected program administrators. Such administrators are subject to a due diligence financial and operational review prior to any such delegation of authority and ongoing reviews and audits are carried out as deemed necessary by our insurance group to assure the continuing integrity of underwriting and related business operations. See "Risk Factors—Risks Relating to Our Company—We could be materially adversely affected to the extent that managing general agents,

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general agents and other producers in our program business exceed their underwriting authorities or otherwise breach obligations owed to us." For information on major brokers, see note 11, "Commitments and Contingencies—Concentrations of Credit Risk," of the notes accompanying our consolidated financial statements.

        Risk Management and Reinsurance.    In the normal course of business, our insurance group may cede a portion of its premium through quota share, surplus share, excess of loss and facultative reinsurance agreements. Reinsurance arrangements do not relieve our insurance group from its obligations to insureds. Reinsurance recoverables are recorded as assets, predicated on the reinsurers' ability to meet their obligations under the reinsurance agreements. If the reinsurers are unable to satisfy their obligations under the agreements, our insurance subsidiaries would be liable for such defaulted amounts. Our insurance subsidiaries, through their respective reinsurance security committees ("RSC"), are selective with regard to reinsurers, seeking to place reinsurance with only those reinsurers which meet and maintain specific standards of established criteria for financial strength. Each RSC evaluates the financial viability of its reinsurers through financial analysis, research and review of rating agencies' reports and also monitors reinsurance recoverables and letters of credit with unauthorized reinsurers and conducts ongoing assessments of reinsurers, including financial stability, appropriate licensing, reputation, claims paying ability and underwriting philosophy. Our insurance group will continue to evaluate its reinsurance requirements. See note 4, "Reinsurance," of the notes accompanying our consolidated financial statements.

        For catastrophe exposed insurance business, our insurance group seeks to limit the amount of exposure to catastrophic losses it assumes through a combination of managing aggregate limits, underwriting guidelines and reinsurance. For a discussion of our risk management policies, see "Management's Discussion and Analysis of Financial Condition and Results of Operations—Critical Accounting Policies, Estimates and Recent Accounting Pronouncements—Ceded Reinsurance" and "Risk Factors—Risks Relating to Our Industry—The failure of any of the loss limitation methods we employ could have a material adverse effect on our financial condition or results of operations."

        Claims Management.    Our insurance group's claims personnel provide underwriting and loss service support to the group. Members of our insurance group's claims departments work with underwriting professionals as functional teams in order to develop products and services that the group's customers desire and, in certain cases, use independent national claims firms (third party administrators) for investigations and field adjustments.

        Our reinsurance operations are conducted on a worldwide basis through our reinsurance subsidiaries, Arch Re Bermuda and Arch Re U.S. Arch Re Bermuda has offices in Bermuda, as well as a branch office in Zurich, Switzerland. Arch Re U.S. operates out of its office in Morristown, New Jersey. Our property facultative reinsurance operations are primarily conducted through Arch Re U.S. with certain executive functions conducted through Arch Re Facultative Underwriters Inc. located in Farmington, Connecticut. Arch Re Denmark is a subsidiary of Arch Re Bermuda which conducts its travel and accident reinsurance operations as a branch office of Arch-Europe. As of February 15, 2008, our reinsurance group had approximately 140 employees.

        Strategy.    Our reinsurance group's strategy is to capitalize on our financial capacity, experienced management and operational flexibility to offer multiple products through our operations. The reinsurance group's operating principles are to:

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        Our reinsurance group writes business on both a proportional and non-proportional basis and writes both treaty and facultative business. In a proportional reinsurance arrangement (also known as pro rata reinsurance, quota share reinsurance or participating reinsurance), the reinsurer shares a proportional part of the original premiums and losses of the reinsured. The reinsurer pays the cedent a commission which is generally based on the cedent's cost of acquiring the business being reinsured (including commissions, premium taxes, assessments and miscellaneous administrative expenses) and may also include a profit factor. Non-proportional (or excess of loss) reinsurance indemnifies the reinsured against all or a specified portion of losses on underlying insurance policies in excess of a specified amount, which is called a "retention." Non-proportional business is written in layers and a reinsurer or group of reinsurers accepts a band of coverage up to a specified amount. The total coverage purchased by the cedent is referred to as a "program." Any liability exceeding the upper limit of the program reverts to the cedent.

        Our reinsurance group generally seeks to write significant lines on less commoditized classes of coverage, such as specialty property and casualty reinsurance treaties. However, with respect to other classes of coverage, such as property catastrophe and casualty clash, our reinsurance group participates in a relatively large number of treaties and assumes smaller lines where it believes that it can underwrite and process the business efficiently.

        Our reinsurance group focuses on the following areas:

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        Underwriting Philosophy.    Our reinsurance group employs a disciplined, analytical approach to underwriting reinsurance risks that is designed to specify an adequate premium for a given exposure commensurate with the amount of capital it anticipates placing at risk. A number of our reinsurance group's underwriters are also actuaries. It is our reinsurance group's belief that employing actuaries on the front-end of the underwriting process gives it an advantage in evaluating risks and constructing a high quality book of business.

        As part of the underwriting process, our reinsurance group typically assesses a variety of factors, including:

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        Premiums Written and Geographic Distribution.    Set forth below is summary information regarding net premiums written for our reinsurance group:

 
   Years Ended December 31,
 
   2007
   2006
   2005
(U.S. dollars in thousands)
   Amount
   % of
Total
   Amount
   % of
Total
   Amount
   % of
Total
Net premiums written                              
Casualty(1)   $ 466,209   39.4   $ 591,219   43.3   $ 753,829   45.5
Property excluding property catastrophe(2)     248,367   21.0     297,080   21.8     339,643   20.5
Property catastrophe     202,203   17.1     146,751   10.7     162,519   9.8
Other specialty     148,776   12.5     218,157   16.0     251,519   15.2
Marine and aviation     110,586   9.3     109,865   8.0     108,981   6.6
Other     8,247   0.7     2,290   0.2     40,981   2.4
   
 
 
 
 
 
Total   $ 1,184,388   100.0   $ 1,365,362   100.0   $ 1,657,472   100.0
   
 
 
 
 
 

Net premiums written by client location
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
United States   $ 688,841   58.1   $ 770,309   56.4   $ 898,980   54.2
Europe     258,952   21.9     368,332   27.0     437,663   26.4
Bermuda     179,935   15.2     132,618   9.7     188,321   11.4
Other     56,660   4.8     94,103   6.9     132,508   8.0
   
 
 
 
 
 
Total   $ 1,184,388   100.0   $ 1,365,362   100.0   $ 1,657,472   100.0
   
 
 
 
 
 

Net premiums written by underwriting location
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Bermuda   $ 691,782   58.4   $ 813,356   59.6   $ 1,004,451   60.6
United States     471,551   39.8     552,006   40.4     653,021   39.4
Other     21,055   1.8     —   —     —   —
   
 
 
 
 
 
Total   $ 1,184,388   100.0   $ 1,365,362   100.0   $ 1,657,472   100.0
   
 
 
 
 
 
(1)
Includes professional liability and executive assurance business.

(2)
Includes facultative business.

        Marketing.    Our reinsurance group markets its reinsurance products through brokers, except our property facultative reinsurance group, which generally deals directly with the ceding companies. Brokers do not have the authority to bind our reinsurance group with respect to reinsurance agreements, nor does our reinsurance group commit in advance to accept any portion of the business that brokers submit to them. Our reinsurance group generally pays brokerage fees to brokers based on negotiated percentages of the premiums written through such brokers. For information on major brokers, see note 11, "Commitments and Contingencies—Concentrations of Credit Risk," of the notes accompanying our consolidated financial statements.

        Risk Management and Retrocession.    Our reinsurance group currently purchases retrocessional coverage as part of their risk management program. They also participate in "common account" retrocessional arrangements for certain treaties. Such arrangements reduce the effect of individual or aggregate losses to all companies participating in such treaties, including the reinsurers. Arch Re Bermuda entered into a quota share reinsurance treaty ("Flatiron Treaty") with Flatiron Re Ltd., a Bermuda reinsurance company, pursuant to which Flatiron Re Ltd. assumed a 45% quota share of certain lines of property and marine business underwritten by Arch Re Bermuda for unaffiliated third

10


parties for the 2006 and 2007 underwriting years (January 1, 2006 to December 31, 2007). Effective June 28, 2006, the parties amended the Flatiron Treaty to increase the percentage ceded to Flatiron Re Ltd. from 45% to 70% of all covered business bound by Arch Re Bermuda from (and including) June 28, 2006 until (and including) August 15, 2006, provided such business did not incept beyond September 30, 2006. The ceding percentage for all business bound outside of this period continued to be 45%. For 2007 and 2006, Arch Re Bermuda ceded $311.3 million and $273.2 million, respectively, of premiums written to Flatiron Re Ltd. ($282.2 million and $157.4 million, respectively, on an earned basis) under the Flatiron Treaty. At December 31, 2007, $144.9 million of premiums ceded to Flatiron Re Ltd. were unearned. The Flatiron Treaty was not renewed upon expiration on December 31, 2007. Our reinsurance group will continue to evaluate its retrocessional requirements. See note 4, "Reinsurance," of the notes accompanying our consolidated financial statements.

        For catastrophe exposed reinsurance business, our reinsurance group seeks to limit the amount of exposure it assumes from any one reinsured and the amount of the aggregate exposure to catastrophe losses from a single event in any one geographic zone. For a discussion of our risk management policies, see "Management's Discussion and Analysis of Financial Condition and Results of Operations—Critical Accounting Policies, Estimates and Recent Accounting Pronouncements—Ceded Reinsurance" and "Risk Factors—Risks Relating to Our Industry—The failure of any of the loss limitation methods we employ could have a material adverse effect on our financial condition or results of operations."

        Claims Management.    Claims management includes the receipt of initial loss reports, creation of claim files, determination of whether further investigation is required, establishment and adjustment of case reserves and payment of claims. Additionally, audits are conducted for both specific claims and overall claims procedures at the offices of selected ceding companies. Our reinsurance group makes use of outside consultants for claims work from time to time.

Employees

        As of February 15, 2008, ACGL and its subsidiaries employed approximately 1,215 full-time employees.

Reserves

        Reserve estimates are derived after extensive consultation with individual underwriters, actuarial analysis of the loss reserve development and comparison with market benchmarks. We have developed our actuarial staff and utilize both internal and external actuaries. Generally, reserves are established without regard to whether we may subsequently contest the claim. We do not currently discount our loss reserves except for excess workers' compensation and employers' liability loss reserves produced by Wexford, a new line of business for us in 2007.

        Loss reserves represent estimates of what the insurer or reinsurer ultimately expects to pay on claims at a given time, based on facts and circumstances then known, and it is probable that the ultimate liability may exceed or be less than such estimates. Even actuarially sound methods can lead to subsequent adjustments to reserves that are both significant and irregular due to the nature of the risks written. Loss reserves are inherently subject to uncertainty. In establishing the reserves for losses and loss adjustment expenses, we have made various assumptions relating to the pricing of our reinsurance contracts and insurance policies and have also considered available historical industry experience and current industry conditions. The timing and amounts of actual claim payments related to recorded reserves vary based on many factors including large individual losses, changes in the legal environment, as well as general market conditions. The ultimate amount of the claim payments could differ materially from our estimated amounts. Certain lines of business written by us, such as excess casualty, have loss experience characterized as low frequency and high severity. This may result in significant

11


variability in loss payment patterns and, therefore, may impact the related asset/liability investment management process in order to be in a position, if necessary, to make these payments. See "Management's Discussion and Analysis of Financial Condition and Results of Operations—Critical Accounting Policies, Estimates and Recent Accounting Pronouncements—Reserves for Losses and Loss Adjustment Expenses."

        The following table represents the development of loss reserves as determined under accounting principles generally accepted in the United States of America ("GAAP") for 1997 through 2007. This table does not present accident or policy year development data. Results for 1997 to 2000 relate to our prior reinsurance operations, which were sold on May 5, 2000 to Folksamerica. With respect to 2000, no reserves are reported in the table below because all reserves for business written through May 5, 2000 were assumed by Folksamerica in the May 5, 2000 asset sale, and we did not write or assume any business during 2000 subsequent to the asset sale. Activity subsequent to 2000 relates to acquisitions made by us and our underwriting initiatives that commenced in October 2001.

        The top line of the table shows the reserves, net of reinsurance recoverables, at the balance sheet date for each of the indicated years. This represents the estimated amounts of net losses and loss adjustment expenses arising in all prior years that are unpaid at the balance sheet date, including incurred but not reported ("IBNR") reserves. The table also shows the re-estimated amount of the previously recorded reserves based on experience as of the end of each succeeding year. The estimate changes as more information becomes known about the frequency and severity of claims for individual years. The "cumulative redundancy (deficiency)" represents the aggregate change in the estimates over all prior years. The table also shows the cumulative amounts paid as of successive years with respect to that reserve liability. In addition, the table reflects the claim development of the gross balance sheet reserves for 1997 through 2007. With respect to the information in the table, it should be noted that each amount includes the effects of all changes in amounts for prior periods.

12


Development of GAAP Reserves
Cumulative Redundancy (Deficiency)

 
   Years Ended December 31,
  
(U.S. dollars in millions)
   1997
   1998
   1999
   2000
   2001
   2002
   2003(a)
   2004
   2005
   2006
   2007
  
Reserve for losses and loss adjustment expenses, net of reinsurance recoverables   $ 71   $ 186   $ 309   —   $ 21   $ 381   $ 1,543   $ 2,875   $ 4,063   $ 4,911   $ 5,483  
Cumulative net paid losses as of:                                                                  
  One year later     19     88     311   —     15     82     278     449     745     843        
  Two years later     33     216     311   —     19     141     437     811     1,332              
  Three years later     64     216     311   —     24     172     596     1,110                    
  Four years later     64     216     311   —     26     204     706                          
  Five years later     64     216     311   —     26     218                                
  Six years later     64     216     311   —     25                                      
  Seven years later     64     216     311   —                                            
  Eight years later     64     216     311                                                
  Nine years later     64     216                                                      
  Ten years later     64                                                            

Net re-estimated reserve as of:
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
  One year later     68     216     311   —     25     340     1,444     2,756     3,986     4,726        
  Two years later     65     216     311   —     25     335     1,353     2,614     3,809              
  Three years later     64     216     311   —     27     335     1,259     2,487                    
  Four years later     64     216     311   —     27     312     1,237                          
  Five years later     64     216     311   —     28     315                                
  Six years later     64     216     311   —     26                                      
  Seven years later     64     216     311   —                                            
  Eight years later     64     216     311                                                
  Nine years later     64     216                                                      
  Ten years later     64                                                            
Cumulative net redundancy (deficiency)   $ 7   $ (30 ) $ (2 ) —   $ (5 ) $ 66   $ 306   $ 388   $ 254   $ 185        
   
 
 
 
 
 
 
 
 
 
       
Cumulative net redundancy (deficiency) as a percentage of net reserves     8.5     (16.1 )   (1.0 ) —     (21.9 )   17.2     19.8     13.5     6.2     3.8        
Gross reserve for losses and loss adjustment expenses   $ 71   $ 216   $ 365   —   $ 111   $ 592   $ 1,912   $ 3,493   $ 5,453   $ 6,463   $ 7,092  
Reinsurance recoverable     —     (30 )   (56 ) —     (90 )   (211 )   (369 )   (618 )   (1,390 )   (1,552 )   (1,609 )
   
 
 
 
 
 
 
 
 
 
 
 
Net reserve for losses and loss adjustment expenses     71     186     309   —     21     381     1,543     2,875     4,063   $ 4,911   $ 5,483  
   
 
 
 
 
 
 
 
 
 
 
 
Gross re-estimated reserve     64     246     367   —     186     562     1,561     3,053     5,203   $ 6,209        
Re-estimated reinsurance recoverable     —     (30 )   (56 ) —     (160 )   (247 )   (324 )   (566 )   (1,394 )   (1,483 )      
   
 
 
 
 
 
 
 
 
 
       
Net re-estimated reserve     64     216     311   —     26     315     1,237     2,487     3,809     4,726        
   
 
 
 
 
 
 
 
 
 
       
Gross re-estimated redundancy (deficiency)   $ 7   $ (30 ) $ (2 ) —   $ (75 ) $ 30   $ 351   $ 440   $ 250   $ 254        
   
 
 
 
 
 
 
 
 
 
       
(a)
Paid amounts include $21.9 million of reserves related to our non-standard automobile business that was sold in 2004 (see "—Our History").

13

        The following table represents an analysis of losses and loss adjustment expenses and a reconciliation of the beginning and ending reserve for losses and loss adjustment expenses.

 
   Years Ended December 31,
  
(U.S. dollars in thousands)
   2007
   2006
   2005
  
Reserve for losses and loss adjustment expenses at beginning of year   $ 6,463,041   $ 5,452,826   $ 3,492,759  
Unpaid losses and loss adjustment expenses recoverable     1,552,157     1,389,768     617,607  
   
 
 
 
Net reserve for losses and loss adjustment expenses at beginning of year     4,910,884     4,063,058     2,875,152  

Increase (decrease) in net losses and loss adjustment expenses incurred relating to losses occurring in:
 
 
 
 
 
 
 
 
 
 
  Current year     1,829,534     1,867,344     2,120,962  
  Prior years     (185,364 )   (76,795 )   (119,013 )
   
 
 
 
    Total net incurred losses and loss adjustment expenses     1,644,170     1,790,549     2,001,949  

Foreign exchange losses (gains)
 
 
45,192
 
 
47,711
 
 
(55,854
)

Less net losses and loss adjustment expenses paid relating to losses occurring in:
 
 
 
 
 
 
 
 
 
 
  Current year     274,102     245,856     308,954  
  Prior years     843,311     744,578     449,235  
   
 
 
 
    Total net paid losses and loss adjustment expenses     1,117,413     990,434     758,189  

Net reserve for losses and loss adjustment expenses at end of year
 
 
5,482,833
 
 
4,910,884
 
 
4,063,058
 
Unpaid losses and loss adjustment expenses recoverable     1,609,619     1,552,157     1,389,768  
   
 
 
 
Reserve for losses and loss adjustment expenses at end of year   $ 7,092,452   $ 6,463,041   $ 5,452,826  
   
 
 
 

        Our reserving method to date has to a large extent been the expected loss method, which is commonly applied when limited loss experience exists. We select the initial expected loss and loss adjustment expense ratios based on information derived by our underwriters and actuaries during the initial pricing of the business, supplemented by industry data where appropriate. These ratios consider, among other things, rate changes and changes in terms and conditions that have been observed in the market. Any estimates and assumptions made as part of the reserving process could prove to be inaccurate due to several factors, including the fact that limited historical information has been reported to us through December 31, 2007. As actual loss information is reported to us and we develop our own loss experience, we will give more emphasis to other actuarial techniques.

        During 2007, on a gross basis, we recorded a redundancy on reserves recorded in prior years of approximately $253.7 million while, on a net basis, we recorded a redundancy on reserves recorded in prior years of approximately $185.4 million. The net favorable development consisted of $172.7 million from the reinsurance segment and $12.7 million from the insurance segment. Of the net favorable development in the reinsurance segment, $110.6 million came from short-tail lines, and $62.1 million came from casualty and marine and aviation business. The development resulted from better than anticipated loss emergence. The net favorable development was partially offset by an increase in acquisition expenses of $18.5 million, primarily as a result of the commutation of certain treaties. In addition, in its reserving process in 2002 and 2003, the reinsurance segment recognized that there is a possibility that the assumptions made could prove to be inaccurate due to several factors primarily related to the start up nature of its operations. Due to the availability of additional data, and based on reserve analyses, it was determined that it was no longer necessary to continue to include such factors

14


in 2004 or subsequent periods. Based on the level of claims activity reported to date, the reinsurance segment reduced the amount of reserves it had recorded in 2002 and 2003 by $10.6 million in 2007. Except as discussed above, the estimated favorable development in the reinsurance segment's prior year reserves did not reflect any significant changes in the key assumptions it made to estimate these reserves at December 31, 2006. As a result of applying a small amount of weight to its own experience, the insurance segment reduced loss selections for some lines, in particular those written on a claims-made basis and for which it now believes it has a reasonable level of credible data. The insurance segment's net favorable development of $12.7 million was primarily due to reductions in reserves in medium-tailed and long-tailed lines of business resulting from such changes, partially offset by adverse development of $33.3 million from short-tail lines which primarily resulted from higher than expected claims development. The net favorable development was partially offset by an increase in acquisition expenses of $9.5 million, primarily due to sliding scale arrangements on certain policies.

        During 2006, on a gross basis, we recorded a deficiency on reserves recorded in prior years of approximately $28.3 million while, on a net basis, we recorded a redundancy on reserves recorded in prior years of approximately $76.8 million. The gross deficiency primarily resulted from adverse development on the 2005 catastrophic events while, on a net basis, a significant portion of the adverse development was covered by reinsurance. The net favorable development consisted of $68.5 million from the reinsurance segment and $8.3 million from the insurance segment. Of the net favorable development in the reinsurance segment, $37.1 million came from short-tail lines, and $31.4 million came from longer-tail lines. The development resulted from better than anticipated loss emergence and was net of $38.1 million of adverse development on the 2005 catastrophic events, primarily in short-tail lines. The net favorable development was partially offset by an increase in acquisition expenses of $7.8 million, primarily as a result of the commutation of certain treaties. As noted above, in its reserving process in 2002 and 2003, the reinsurance segment recognized that there is a possibility that the assumptions made could prove to be inaccurate due to several factors primarily related to the start up nature of its operations. Due to the availability of additional data, and based on reserve analyses, it was determined that it was no longer necessary to continue to include such factors. Following reserve reviews, and based on the level of claims activity reported to date, the reinsurance segment reduced the amount of reserves it had recorded in 2002 and 2003 by $7.7 million in 2006. Except as discussed above, the estimated favorable development in the reinsurance segment's prior year reserves did not reflect any significant changes in the key assumptions it made to estimate these reserves at December 31, 2005. The insurance segment's net favorable development of $8.3 million was primarily due to reductions in reserves in certain medium-tailed and long-tailed lines of business, in particular for those lines of business written on a claims-made basis and for which it now believes it has a reasonable level of credible data, partially offset by adverse development of $44.0 million from short-tail lines which included $30.8 million of adverse development on the 2005 catastrophic events.

        During 2005, on a gross and net basis, we recorded a redundancy on reserves recorded in prior years of approximately $113.9 million and $119.0 million, respectively. The net favorable development consisted of $91.2 million from the reinsurance segment and $27.8 million from the insurance segment. Of the net favorable development in the reinsurance segment, $85.3 million was primarily due to short-tail lines, mainly property, and resulted from better than anticipated loss emergence. Such amount was partially offset by an increase in acquisition expenses of $9.0 million, primarily as a result of the commutation of certain treaties. As noted above, in its reserving process in 2002 and 2003, the reinsurance segment recognized that there is a possibility that the assumptions made could prove to be inaccurate due to several factors primarily related to the start up nature of its operations. Following reserve reviews, and based on the level of claims activity reported to date, the reinsurance segment reduced the amount of reserves it had recorded in 2002 and 2003 by $12.1 million in 2005. Except as discussed above, the estimated favorable development in the reinsurance segment's prior year reserves did not reflect any significant changes in the key assumptions it made to estimate these reserves at December 31, 2004. Prior to 2005, the insurance segment's reserving method relied heavily on industry

15


data. In 2005, the insurance segment began to give a relatively small amount of weight to its own experience. The insurance segment's net favorable development of $27.8 million was primarily due to reductions in reserves in certain medium-tailed and long-tailed lines of business, in particular for those lines of business written on a claims-made basis and for which it now believes it has a reasonable level of credible data.

        We are subject to credit risk with respect to our reinsurance and retrocessions because the ceding of risk to reinsurers and retrocessionaires does not relieve us of our liability to the clients or companies we insure or reinsure. Our failure to establish adequate reinsurance or retrocessional arrangements or the failure of our existing reinsurance or retrocessional arrangements to protect us from overly concentrated risk exposure could adversely affect our financial condition and results of operations. Although we monitor the financial condition of our reinsurers and retrocessionaires and attempt to place coverages only with substantial, financially sound carriers, we may not be successful in doing so. See "Management's Discussion and Analysis of Financial Condition and Results of Operations—Critical Accounting Policies, Estimates and Recent Accounting Pronouncements—Collection of Insurance-Related Balances and Provision for Doubtful Accounts."

Investments

        At December 31, 2007, consolidated cash and invested assets totaled approximately $10.13 billion, consisting of $939.0 million of cash and short-term investments, $8.6 billion of fixed maturities and fixed maturities pledged under securities lending agreements and $589.7 million of other investments. See "Management's Discussion and Analysis of Financial Condition and Results of Operations—Critical Accounting Policies, Estimates and Recent Accounting Pronouncements—Investments."

        The following table summarizes the fair value of our cash and invested assets at December 31, 2007 and 2006:

 
   December 31,
 
   2007
   2006
(U.S. dollars in thousands)
   Estimated
Fair Value
   % of
Total
   Estimated
Fair Value
   % of
Total
Cash and short-term investments(1)   $ 938,951   9.3   $ 1,274,715   13.7
   
 
 
 
Fixed maturities and fixed maturities pledged under securities lending agreements(1):                    
  Corporate bonds     2,452,527   24.2     1,504,989   16.2
  Commercial mortgage backed securities     1,315,680   13.0     868,586   9.3
  Mortgage backed securities     1,234,596   12.2     1,183,805   12.7
  U.S. government and government agencies     1,165,423   11.5     1,922,511   20.6
  Asset backed securities     1,008,030   9.9     907,829   9.7
  Municipal bonds     990,325   9.8     815,204   8.8
  Non-U.S. government securities     434,243   4.3     534,427   5.7
   
 
 
 
    Sub-total     8,600,824   84.9     7,737,351   83.0
   
 
 
 
Short-term investments pledged under securities lending agreements, at fair value(1)     219   0.0     —   —
Other investments     589,669   5.8     307,082   3.3
   
 
 
 
    Total cash and invested assets(1)(2)   $ 10,129,663   100.0   $ 9,319,148   100.0
   
 
 
 
(1)
In our securities lending transactions, we receive collateral in excess of the fair value of the fixed maturities and short-term investments pledged under securities lending agreements. For purposes of this table, we have excluded $1.5 billion and $891.4 million, respectively, of collateral received

16

(2)
Includes certain securities transactions entered into but not settled at the balance sheet date. Net of such amounts, total cash and investments were approximately $10.12 billion at December 31, 2007 and $9.09 billion at December 31, 2006.

        Our current investment guidelines and approach stress preservation of capital, market liquidity and diversification of risk. Our investments are subject to market-wide risks and fluctuations, as well as to risks inherent in particular securities. At December 31, 2007 and 2006, approximately 98% of our fixed maturities and fixed maturities pledged under securities lending agreements were rated investment grade by the major rating agencies, primarily Standard & Poor's Rating Services ("Standard & Poor's"). At December 31, 2007 and 2006, our fixed maturities, fixed maturities pledged under securities lending agreements and short-term investments had an average credit quality rating of "AA+" and "AAA", respectively, and an average effective duration of approximately 3.29 years and 3.23 years, respectively.

        During the 2005 third quarter, we began a securities lending program under which certain of our fixed income portfolio securities are loaned to third parties, primarily major brokerage firms, for short periods of time through a lending agent. Such securities have been reclassified as "Fixed maturities and short-term investments pledged under securities lending agreements, at fair value." We maintain control over the securities we lend, retain the earnings and cash flows associated with the loaned securities and receive a fee from the borrower for the temporary use of the securities. Collateral received, primarily in the form of cash, is required at a rate of 102% of the fair value of the loaned securities (or 105% of the fair value of the loaned securities when the collateral and loaned securities are denominated in non-U.S. currencies) including accrued investment income and is monitored and maintained by the lending agent. Such collateral is reinvested and is reflected as "Short-term investment of funds received under securities lending agreements, at fair value." At December 31, 2007, the fair value and amortized cost of fixed maturities and short-term investments pledged under securities lending agreements were $1.46 billion and $1.44 billion, respectively, while collateral received totaled $1.5 billion at fair value and amortized cost. At December 31, 2006, the fair value and amortized cost of fixed maturities and short-term investments pledged under securities lending agreements were $860.8 million and $854.8 million, respectively, while collateral received totaled $891.4 million at fair value and amortized cost.

        The credit quality distribution of our fixed maturities and fixed maturities pledged under securities lending agreements at December 31, 2007 and 2006 are shown below:

(U.S. dollars in thousands)
   December 31, 2007
   December 31, 2006
Rating(1)
   Estimated
Fair Value
   % of
Total
   Estimated
Fair Value
   % of
Total
AAA   $ 6,600,258   76.7   $ 6,366,059   82.3
AA     882,262   10.3     605,427   7.8
A     677,047   7.9     430,103   5.6
BBB     243,610   2.8     194,408   2.5
BB     25,390   0.3     32,572   0.4
B     128,459   1.5     64,636   0.8
Lower than B     11,321   0.1     11,149   0.2
Not rated     32,477   0.4     32,997   0.4
   
 
 
 
  Total   $ 8,600,824   100.0   $ 7,737,351   100.0
   
 
 
 
(1)
Ratings as assigned by the major rating agencies.

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        For 2007 and 2006, set forth below is the pre-tax total return (before investment expenses) of our investment portfolio (including fixed maturities, short-term investments and fixed maturities and short-term investments pledged under securities lending agreements) compared to the benchmark return against which we measured our portfolio during the year. Our investment expenses were approximately 0.15% of average invested assets in 2007 and 2006.

 
   Arch
Portfolio
   Benchmark
Return(1)
Pre-tax total return (before investment expenses):        
  Year ended December 31, 2007   6.52%   6.97%
  Year ended December 31, 2006   5.24%   4.88%
(1)
The benchmark return is a weighted average of the benchmarks assigned to each of our investment managers. The benchmarks used vary based on the nature of the portfolios under management. In all but a few instances, the benchmarks used are Lehman indices.

Ratings

        The Company's ability to underwrite business is dependent upon the quality of its claims paying ability and financial strength ratings as evaluated by independent agencies. Such ratings from third party internationally recognized statistical rating organizations or agencies are instrumental in establishing the competitive positions of companies in our industry. The Company believes that the primary users of such ratings include commercial and investment banks, policyholders, brokers, ceding companies and investors. Insurance ratings are also used by insurance and reinsurance intermediaries as an important means of assessing the financial strength and quality of insurers and reinsurers, and have become an increasingly important factor in establishing the competitive position of insurance and reinsurance companies. These ratings are often an important factor in the decision by an insured or intermediary of whether to place business with a particular insurance or reinsurance provider. Periodically, rating agencies evaluate us to confirm that we continue to meet their criteria for the ratings assigned to us by them. A.M. Best Company maintains a letter scale rating system ranging from "A++" (Superior) to "F" (In Liquidation). Moody's Investors Service maintains a letter scale rating from "Aaa" (Exceptional) to "NP" (Not Prime). Standard & Poor's maintains a letter scale rating system ranging from "AAA" (Extremely Strong) to "R" (Under Regulatory Supervision). Our reinsurance subsidiaries, Arch Re U.S. and Arch Re Bermuda, and our principal insurance subsidiaries, Arch Insurance, Arch E&S, Arch Specialty and Arch-Europe, each currently has a financial strength rating of "A" (Excellent, the third highest out of fifteen rating levels) with a stable outlook from A.M. Best Company, "A2" (Good, the sixth highest out of 21 rating levels) with a stable outlook from Moody's Investors Service and "A" (Strong, the sixth highest out of 21 rating levels) with a positive outlook from Standard and Poor's. Fitch Ratings has assigned a financial strength rating of "A" (Strong, the sixth highest out of 24 rating levels) with a stable outlook to Arch Re Bermuda. A.M. Best Company has assigned a financial strength rating of "NR-3" (Rating Procedure Inapplicable) to Western Diversified, which currently is not writing business, and Moody's Investors Service and Standard & Poor's did not rate Western Diversified.

        ACGL has received counterparty (issuer) credit ratings of "BBB+" (eighth highest out of 22 rating levels) with a positive outlook from Standard & Poor's, "Baa1" (eighth highest out of 21 rating levels) with a stable outlook from Moody's Investors Service and "A-" long term issuer rating (seventh highest out of 23 rating levels) with a stable outlook from Fitch Ratings. A counterparty credit rating provides an opinion on an issuer's overall capacity and willingness to meet its financial commitments as they become due, but is not specific to a particular financial obligation. ACGL's senior debt was assigned a rating of "BBB+" from Standard and Poors, "Baa1" from Moody's Investors Service and "BBB+" from Fitch Ratings. ACGL's series A non-cumulative preferred shares and series B non-cumulative

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preferred shares were both assigned a "BBB-" rating by Standard & Poor's, a "Baa3" by Moody's Investors Service and a "BBB" rating by Fitch Ratings.

        The objective of these ratings systems is to assist policyholders and to provide an opinion of an insurer's or reinsurer's financial strength and ability to meet ongoing obligations to its policyholders. The financial strength ratings assigned by rating agencies to insurance and reinsurance companies represent independent opinions of financial strength and ability to meet policyholder obligations and are not directed toward the protection of investors, nor are they recommendations to buy, hold or sell any securities. We can offer no assurances that our ratings will remain at their current levels, or that our security will be accepted by brokers and our insureds and reinsureds. A ratings downgrade or the potential for such a downgrade, or failure to obtain a necessary rating, could adversely affect both our relationships with agents, brokers, wholesalers and other distributors of our existing products and services and new sales of our products and services. In addition, under certain of the reinsurance agreements assumed by our reinsurance operations, upon the occurrence of a ratings downgrade or other specified triggering event with respect to our reinsurance operations, such as a reduction in surplus by specified amounts during specified periods, our ceding company clients may be provided with certain rights, including, among other things, the right to terminate the subject reinsurance agreement and/or to require that our reinsurance operations post additional collateral. In the event of a ratings downgrade or other triggering event, the exercise of such contract rights by our clients could have a material adverse effect on our financial condition and results of operations, as well as our ongoing business and operations. See "Management's Discussion and Analysis of Financial Condition and Results of Operations—Liquidity and Capital Resources."

Competition

        The worldwide reinsurance and insurance businesses are highly competitive. We compete, and will continue to compete, with major U.S. and non-U.S. insurers and reinsurers, some of which have greater financial, marketing and management resources than we have and have had longer-term relationships with insureds and brokers than us. We compete with other insurers and reinsurers primarily on the basis of overall financial strength, ratings assigned by independent rating agencies, geographic scope of business, strength of client relationships, premiums charged, contract terms and conditions, products and services offered, speed of claims payment, reputation, employee experience, and qualifications and local presence. We also compete with new companies that continue to be formed to enter the insurance and reinsurance markets.

        In our insurance business, we compete with insurers that provide specialty property and casualty lines of insurance, including: ACE Limited, Allied World Assurance Company, Ltd., American International Group, Inc., AXIS Capital Holdings Limited, Berkshire Hathaway, Inc., Chubb Corporation, Endurance Specialty Holdings Ltd., The Hartford Financial Services Group, Inc., HCC Insurance Holdings, Inc., Lloyd's of London, The St. Paul Travelers Companies, W.R. Berkley Corp., XL Capital Ltd. and Zurich Insurance Group. In our reinsurance business, we compete with reinsurers that provide property and casualty lines of reinsurance, including ACE Limited, AXIS Capital Holdings Limited, Berkshire Hathaway, Inc., Endurance Specialty Holdings Ltd., Everest Re Group Ltd., Hannover Rückversicherung AG, Lloyd's of London, Montpelier Re Holdings Ltd., Munich Re Group, PartnerRe Ltd., Platinum Underwriters Holdings, Ltd., RenaissanceRe Holdings Ltd., Swiss Reinsurance Company, Transatlantic Holdings, Inc. and XL Capital Ltd. We do not believe that we have a significant market share in any of our markets.

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Regulation

        General.    In common with other insurers, our U.S.-based insurance subsidiaries are subject to extensive governmental regulation and supervision in the various states and jurisdictions in which they are domiciled and licensed and/or approved to conduct business. The laws and regulations of the state of domicile have the most significant impact on operations. This regulation and supervision is designed to protect policyholders rather than investors. Generally, regulatory authorities have broad regulatory powers over such matters as licenses, standards of solvency, premium rates, policy forms, marketing practices, claims practices, investments, security deposits, methods of accounting, form and content of financial statements, reserves and provisions for unearned premiums, unpaid losses and loss adjustment expenses, reinsurance, minimum capital and surplus requirements, dividends and other distributions to shareholders, periodic examinations and annual and other report filings. In addition, transactions among affiliates, including reinsurance agreements or arrangements, as well as certain third party transactions, require prior regulatory approval from, or prior notice to, the applicable regulator under certain circumstances. Certain insurance regulatory requirements are highlighted below. In addition, regulatory authorities conduct periodic financial, claims and market conduct examinations. Arch-Europe is also subject to certain governmental regulation and supervision in the various states where it has been approved as an excess and surplus lines insurer.

        The New York Attorney General, various state insurance regulatory authorities and others are investigating contingent commission payments to brokers (and the disclosures relating to such payments), alleged "bid-rigging," "steering," and other practices in the insurance industry involving brokers and agents, as well as certain finite insurance and/or reinsurance products. Although certain brokers have announced new fee structures in response to the industry investigations and, as part of these new initiatives, have requested that our insurance subsidiaries enter into standardized payment arrangements, we have determined to negotiate payment arrangements with our brokers on a case by case basis. We cannot predict the effect that these investigations, and any changes in industry practice, including future legislation or regulations that may become applicable to us, will have on the insurance industry or our business. See "Risk Factors—Risks Relating to Our Industry—Our reliance on brokers subjects us to their credit risk."

        Credit for Reinsurance.    Arch Re U.S. is subject to insurance regulation and supervision that is similar to the regulation of licensed primary insurers. However, except for certain mandated provisions that must be included in order for a ceding company to obtain credit for reinsurance ceded, the terms and conditions of reinsurance agreements generally are not subject to regulation by any governmental authority. This contrasts with admitted primary insurance policies and agreements, the rates and terms of which generally are regulated by state insurance regulators. As a practical matter, however, the rates charged by primary insurers do have an effect on the rates that can be charged by reinsurers.

        A primary insurer ordinarily will enter into a reinsurance agreement only if it can obtain credit for the reinsurance ceded on its U.S. statutory-basis financial statements. In general, credit for reinsurance is allowed in the following circumstances:

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        As a result of the requirements relating to the provision of credit for reinsurance, Arch Re U.S. and Arch Re Bermuda are indirectly subject to certain regulatory requirements imposed by jurisdictions in which ceding companies are licensed.

        As of February 15, 2008: (1) Arch Re U.S. is licensed or is an accredited or otherwise approved reinsurer in 50 states and the District of Columbia; (2) Arch Insurance is licensed as an insurer in 50 states, the District of Columbia, Puerto Rico and, the U.S. Virgin Islands with a branch office in Canada; (3) Arch Specialty is licensed in one state and approved as an excess and surplus lines insurer in 49 states, the District of Columbia, Puerto Rico and the U.S. Virgin Islands; (4) Arch E&S is licensed in one state and approved as an excess and surplus lines insurer in 46 states and the District of Columbia; (5) Western Diversified is licensed as an insurer in 48 states and the District of Columbia; and (6) Arch-Europe is approved as an excess and surplus lines insurer in 14 states. Arch Re Bermuda does not expect to become, licensed, accredited or so approved in any U.S. jurisdiction.

        Holding Company Acts.    All states have enacted legislation that regulates insurance holding company systems. These regulations generally provide that each insurance company in the system is required to register with the insurance department of its state of domicile and furnish information concerning the operations of companies within the holding company system which may materially affect the operations, management or financial condition of the insurers within the system. All transactions within a holding company system affecting insurers must be fair and reasonable. Notice to the insurance departments is required prior to the consummation of transactions affecting the ownership or control of an insurer and of certain material transactions between an insurer and any entity in its holding company system. In addition, certain of such transactions cannot be consummated without the applicable insurance department's prior approval.

        Regulation of Dividends and Other Payments from Insurance Subsidiaries.    The ability of an insurer to pay dividends or make other distributions is subject to insurance regulatory limitations of the insurance company's state of domicile. Generally, such laws limit the payment of dividends or other distributions above a specified level. Dividends or other distributions in excess of such thresholds are "extraordinary" and are subject to prior regulatory approval. Such dividends or distributions may be subject to applicable withholding or other taxes. See "Management's Discussion and Analysis of Financial Condition and Results of Operations—Liquidity and Capital Resources" and note 15, "Statutory Information," of the notes accompanying our financial statements.

        Insurance Regulatory Information System Ratios.    The National Association of Insurance Commissioners ("NAIC") Insurance Regulatory Information System ("IRIS") was developed by a committee of state insurance regulators and is intended primarily to assist state insurance departments in executing their statutory mandates to oversee the financial condition of insurance companies operating in their respective states. IRIS identifies 13 industry ratios (referred to as "IRIS ratios") and specifies "usual values" for each ratio. Departure from the usual values of the IRIS ratios can lead to inquiries from individual state insurance commissioners as to certain aspects of an insurer's business. For 2007, certain of our U.S.-based subsidiaries generated IRIS ratios that were outside of the usual values. To date, none of these subsidiaries has received any notice of regulatory review but there is no assurance that we may not be notified in the future.

        Accreditation.    The NAIC has instituted its Financial Regulatory Accreditation Standards Program ("FRASP") in response to federal initiatives to regulate the business of insurance. FRASP provides a set of standards designed to establish effective state regulation of the financial condition of insurance

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companies. Under FRASP, a state must adopt certain laws and regulations, institute required regulatory practices and procedures, and have adequate personnel to enforce such items in order to become an "accredited" state. If a state is not accredited, other states may not accept certain financial examination reports of insurers prepared solely by the regulatory agency in such unaccredited state. The respective states in which Arch Re U.S., Arch Insurance, Arch E&S, Arch Specialty and Western Diversified are domiciled are accredited states.

        Risk-Based Capital Requirements.    In order to enhance the regulation of insurer solvency, the NAIC adopted in December 1993 a formula and model law to implement risk-based capital requirements for property and casualty insurance companies. These risk-based capital requirements are designed to assess capital adequacy and to raise the level of protection that statutory surplus provides for policyholder obligations. The risk-based capital model for property and casualty insurance companies measures three major areas of risk facing property and casualty insurers:

        An insurer will be subject to varying degrees of regulatory action depending on how its statutory surplus compares to its risk-based capital calculation. Equity investments in common stock typically are valued at 85% of their market value under the risk-based capital guidelines. For equity investments in an insurance company affiliate, the risk-based capital requirements for the equity securities of such affiliate would generally be our U.S. insurance subsidiaries' proportionate share of the affiliate's risk-based capital requirement.

        Under the approved formula, an insurer's total adjusted capital is compared to its authorized control level risk-based capital. If this ratio is above a minimum threshold, no company or regulatory action is necessary. Below this threshold are four distinct action levels at which a regulator can intervene with increasing degrees of authority over an insurer as the ratio of surplus to risk-based capital requirement decreases. The four action levels include:

        Each of our U.S. insurance subsidiaries' surplus (as calculated for statutory purposes) is above the risk-based capital thresholds that would require either company or regulatory action.

        Guaranty Funds and Assigned Risk Plans.    Most states require all admitted insurance companies to participate in their respective guaranty funds which cover certain claims against insolvent insurers. Solvent insurers licensed in these states are required to cover the losses paid on behalf of insolvent insurers by the guaranty funds and are generally subject to annual assessments in the states by the guaranty funds to cover these losses. Participation in state-assigned risk plans may take the form of reinsuring a portion of a pool of policies or the direct issuance of policies to insureds. The calculation of an insurer's participation in these plans is usually based on the amount of premium for that type of coverage that was written by the insurer on a voluntary basis in a prior year. Assigned risk pools tend to produce losses which result in assessments to insurers writing the same lines on a voluntary basis.

        Federal Regulation.    Although state regulation is the dominant form of regulation for insurance and reinsurance business, the federal government has shown increasing concern over the adequacy of state regulation. It is not possible to predict the future impact of any potential federal regulations or

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other possible laws or regulations on our U.S. subsidiaries' capital and operations, and such laws or regulations could materially adversely affect their business.

        Terrorism Risk Insurance Program Reauthorization Act of 2007.    On November 26, 2002, President Bush signed into law the Terrorism Risk Insurance Act of 2002, which was amended and extended by the Terrorism Risk Insurance Extension Act of 2005 and amended and extended again by the Terrorism Risk Insurance Program Reauthorization Act of 2007 ("TRIPRA") through December 31, 2014. TRIPRA provides a federal backstop for insurance-related losses resulting from any act of terrorism on U.S. soil or against certain U.S. air carriers, vessels or foreign missions. Under TRIPRA, all U.S.-based property and casualty insurers are required to make terrorism insurance coverage available in specified commercial property and casualty insurance lines. Under TRIPRA, the federal government will pay 85% of covered losses after an insurer's losses exceed a deductible determined by a statutorily prescribed formula, up to a combined annual aggregate limit for the federal government and all insurers of $100 billion. If an act (or acts) of terrorism result in covered losses exceeding the $100 billion annual limit, insurers with losses exceeding their deductibles will not be responsible for additional losses. The deductible for each year is based on the insurer's direct commercial earned premiums for property and casualty insurance, excluding certain lines of business such as commercial auto, surety, professional liability and earthquake lines of business, for the prior calendar year multiplied by 20%. The specified percentages for prior periods were 7% for 2003, 10% for 2004, 15% for 2005, 17.5% for 2006 and 20% for 2007, which extends through 2014.

        Our U.S.-based property and casualty insurers, Arch Insurance, Arch Specialty, Arch E&S and Western Diversified, are subject to TRIPRA. TRIPRA specifically excludes reinsurance business and, accordingly, does not apply to our reinsurance operations. Our U.S. insurance group's deductible for 2007 was approximately $274 million (i.e., 20.0% of earned premiums). Based on 2007 direct commercial earned premiums, our U.S. insurance group's deductible for 2008 is approximately $261.7 million (i.e., 20.0% of such earned premiums).

        The Gramm-Leach-Bliley Act.    The Gramm-Leach-Bliley Act of 1999 ("GLBA"), which implements fundamental changes in the regulation of the financial services industry in the United States, was enacted on November 12, 1999. The GLBA permits the transformation of the already converging banking, insurance and securities industries by permitting mergers that combine commercial banks, insurers and securities firms under one holding company, a "financial holding company." Bank holding companies and other entities that qualify and elect to be treated as financial holding companies may engage in activities, and acquire companies engaged in activities, that are "financial" in nature or "incidental" or "complementary" to such financial activities. Such financial activities include acting as principal, agent or broker in the underwriting and sale of life, property, casualty and other forms of insurance and annuities.

        Until the passage of the GLBA, the Glass-Steagall Act of 1933 had limited the ability of banks to engage in securities-related businesses, and the Bank Holding Company Act of 1956 had restricted banks from being affiliated with insurers. With the passage of the GLBA, among other things, bank holding companies may acquire insurers, and insurance holding companies may acquire banks. The ability of banks to affiliate with insurers may affect our U.S. subsidiaries' product lines by substantially increasing the number, size and financial strength of potential competitors.

        Legislative and Regulatory Proposals.    From time to time various regulatory and legislative changes have been proposed in the insurance and reinsurance industry. Among the proposals that have in the past been or are at present being considered are the possible introduction of federal regulation in addition to, or in lieu of, the current system of state regulation of insurers. In addition, there are a variety of proposals being considered by various state legislatures. We are unable to predict whether any of these proposed laws and regulations will be adopted, the form in which any such laws and regulations would be adopted, or the effect, if any, these developments would have on our operations and financial condition. See "—U.S. Insurance Regulation—General."

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        The Insurance Act 1978, as Amended, and Related Regulations of Bermuda (the "Insurance Act").    As a holding company, ACGL is not subject to Bermuda insurance regulations. The Insurance Act, which regulates the insurance business of Arch Re Bermuda, provides that no person shall carry on any insurance business in or from within Bermuda unless registered as an insurer under the Insurance Act by the Bermuda Monetary Authority (the "BMA"), which is responsible for the day-to-day supervision of insurers. Under the Insurance Act, insurance business includes reinsurance business. The registration of an applicant as an insurer is subject to its complying with the terms of its registration and such other conditions as the BMA may impose from time to time.

        The Insurance Act imposes solvency and liquidity standards and auditing and reporting requirements on Bermuda insurance companies and grants to the BMA powers to supervise, investigate and intervene in the affairs of insurance companies. Certain significant aspects of the Bermuda insurance regulatory framework are set forth below.

        Classification of Insurers.    The Insurance Act distinguishes between insurers carrying on long-term business and insurers carrying on general business. There are four classifications of insurers carrying on general business, with Class 4 insurers subject to the strictest regulation. Arch Re Bermuda is registered as both a long-term insurer and a Class 4 insurer in Bermuda, which we refer to in this annual report as a composite insurer, and is regulated as such under the Insurance Act.

        Cancellation of Insurer's Registration.    An insurer's registration may be canceled by the BMA on certain grounds specified in the Insurance Act, including failure of the insurer to comply with its obligations under the Insurance Act or if, in the opinion of the BMA, the insurer has not been carrying on business in accordance with sound insurance principles. We believe we are in compliance with applicable regulations under the Insurance Act.

        Principal Representative.    An insurer is required to maintain a principal office in Bermuda and to appoint and maintain a principal representative in Bermuda. It is the duty of the principal representative upon reaching the view that there is a likelihood of the insurer for which the principal representative acts becoming insolvent or that a reportable "event" has, to the principal representative's knowledge, occurred or is believed to have occurred, to immediately notify the BMA and to make a report in writing to the BMA within 14 days setting out all the particulars of the case that are available to the principal representative.

        Approved Independent Auditor.    Every registered insurer must appoint an independent auditor who annually audits and reports on the statutory financial statements and the statutory financial return of the insurer, both of which, in the case of Arch Re Bermuda, are required to be filed annually with the BMA. The independent auditor must be approved by the BMA.

        Approved Actuary.    Arch Re Bermuda, as a registered long-term insurer, is required to submit an annual actuary's certificate when filing its statutory financial returns. The actuary, who is normally a qualified life actuary, must be approved by the BMA.

        Approved Loss Reserve Specialist.    As a registered Class 4 insurer, Arch Re Bermuda is required to submit an opinion of its approved loss reserve specialist with its statutory financial return in respect of its loss and loss expense provisions. The loss reserve specialist, who will normally be a qualified casualty actuary, must be approved by the BMA.

        Annual Statutory Financial Statements.    An insurer must prepare annual statutory financial statements. The Insurance Act prescribes rules for the preparation and substance of such statutory financial statements (which include, in statutory form, a balance sheet, an income statement, a statement of capital and surplus and notes thereto). The insurer is required to give detailed

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information and analyses regarding premiums, claims, reinsurance and investments. The statutory financial statements are not prepared in accordance with GAAP and are distinct from the financial statements prepared for presentation to the insurer's shareholders under the Companies Act 1981 of Bermuda (the "Companies Act"), which financial statements are prepared in accordance with GAAP. Arch Re Bermuda, as a general business insurer, is required to submit the annual statutory financial statements as part of the annual statutory financial return.

        Annual Statutory Financial Return.    Arch Re Bermuda is required to file with the BMA in Bermuda a statutory financial return no later than four months after its financial year end (unless specifically extended upon application to the BMA). The statutory financial return for a Class 4 insurer includes, among other matters, a report of the approved independent auditor on the statutory financial statements of such insurer, solvency certificates, the statutory financial statements themselves, the opinion of the loss reserve specialist and a schedule of reinsurance ceded.

        Minimum Solvency Margin and Restrictions on Dividends and Distributions.    Under the Insurance Act, Arch Re Bermuda must ensure that the value of its long-term business assets exceed the amount of its long-term business liabilities by at least $250,000. The Insurance Act also provides that the value of the general business assets of Arch Re Bermuda, as a Class 4 insurer, must exceed the amount of its general business liabilities by an amount greater than the prescribed minimum solvency margin. Arch Re Bermuda:

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        Minimum Liquidity Ratio.    The Insurance Act provides a minimum liquidity ratio for general business insurers such as Arch Re Bermuda. An insurer engaged in general business is required to maintain the value of its relevant assets at not less than 75% of the amount of its relevant liabilities. Relevant assets include cash and time deposits, quoted investments, unquoted bonds and debentures, first liens on real estate, investment income due and accrued, accounts and premiums receivable and reinsurance balances receivable. The relevant liabilities are total general business insurance reserves and total other liabilities less deferred income tax and sundry liabilities (by interpretation, those not specifically defined).

        Long-Term Business Fund.    An insurer carrying on long-term business is required to keep its accounts in respect of its long-term business separate from any accounts kept in respect of any other business and all receipts of its long-term business form part of its long-term business fund. No payment may be made directly or indirectly from an insurer's long-term business fund for any purpose other than a purpose related to the insurer's long-term business, unless such payment can be made out of any surplus certified by the insurer's approved actuary to be available for distribution otherwise than to policyholders. Arch Re Bermuda may not declare or pay a dividend to any person other than a policyholder unless the value of the assets in its long-term business fund, as certified by its approved actuary, exceeds the liabilities of the insurer's long-term business (as certified by the insurer's approved actuary) by the amount of the dividend and at least the $250,000 minimum solvency margin prescribed by the Insurance Act, and the amount of any such dividend may not exceed the aggregate of that excess (excluding the said $250,000) and any other funds properly available for payment of dividends, such as funds arising out of business of the insurer other than long-term business.

        Restrictions on Transfer of Business and Winding-Up.    Arch Re Bermuda, as a long-term insurer, is subject to the following provisions of the Insurance Act:

        Supervision, Investigation and Intervention.    The BMA may appoint an inspector with extensive powers to investigate the affairs of an insurer if the BMA believes that an investigation is required in the interest of the insurer's policyholders or persons who may become policyholders. In order to verify or supplement information otherwise provided to the BMA, the BMA may direct an insurer to produce documents or information relating to matters connected with the insurer's business.

        If it appears to the BMA that there is a risk of the insurer becoming insolvent, or that it is in breach of the Insurance Act or any conditions imposed upon its registration, the BMA may, among other things, direct the insurer (1) not to take on any new insurance business, (2) not to vary any insurance contract if the effect would be to increase the insurer's liabilities, (3) not to make certain investments, (4) to realize certain investments, (5) to maintain in, or transfer to the custody of, a

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specified bank, certain assets, (6) not to declare or pay any dividends or other distributions or to restrict the making of such payments and/or (7) to limit its premium income.

        Shareholder Controllers.    Any person who, directly or indirectly, becomes a holder of at least 10%, 20%, 33% or 50% of the common shares of ACGL must notify the BMA in writing within 45 days of becoming such a holder or 30 days from the date such person has knowledge of having such a holding, whichever is later. The BMA may, by written notice, object to such a person if it appears to the BMA that the person is not fit and proper to be such a holder. The BMA may require the holder to reduce their holding of common shares in ACGL and direct, among other things, that voting rights attaching to the common shares shall not be exercisable. A person that does not comply with such a notice or direction from the BMA will be guilty of an offense.

        For so long as ACGL has as a subsidiary an insurer registered under the Insurance Act, the BMA may at any time, by written notice, object to a person holding 10% or more of its common shares if it appears to the BMA that the person is not or is no longer fit and proper to be such a holder. In such a case, the BMA may require the shareholder to reduce its holding of common shares in ACGL and direct, among other things, that such shareholder's voting rights attaching to the common shares shall not be exercisable. A person who does not comply with such a notice or direction from the BMA will be guilty of an offense.

        ACGL and Arch Re Bermuda have been designated as non-resident for exchange control purposes by the BMA and are required to obtain the permission of the BMA for the issue and transfer of all of their shares. The BMA has given its consent for:

        Transfers and issues of ACGL's common shares to any resident in Bermuda for exchange control purposes may require specific prior approval under the Exchange Control Act 1972. Arch Re Bermuda's common shares cannot be issued or transferred without the consent of the BMA. Because we are designated as non-resident for Bermuda exchange control purposes, we are allowed to engage in transactions, and to pay dividends to Bermuda non-residents who are holders of our common shares, in currencies other than the Bermuda Dollar.

        In accordance with Bermuda law, share certificates are issued only in the names of corporations or individuals. In the case of an applicant acting in a special capacity (for example, as an executor or trustee), certificates may, at the request of the applicant, record the capacity in which the applicant is acting. Notwithstanding the recording of any such special capacity, we are not bound to investigate or incur any responsibility in respect of the proper administration of any such estate or trust. We will take no notice of any trust applicable to any of our common shares whether or not we have notice of such trust.

        ACGL and Arch Re Bermuda are incorporated in Bermuda as "exempted companies." As a result, they are exempt from Bermuda laws restricting the percentage of share capital that may be held by non-Bermudians, but they may not participate in certain business transactions, including (1) the acquisition or holding of land in Bermuda (except that required for their business and held by way of lease or tenancy for terms of not more than 50 years) without the express authorization of the Bermuda legislature, (2) the taking of mortgages on land in Bermuda to secure an amount in excess of $50,000 without the consent of the Minister of Finance, (3) the acquisition of any bonds or debentures

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secured by any land in Bermuda, other than certain types of Bermuda government securities or (4) the carrying on of business of any kind in Bermuda, except in furtherance of their business carried on outside Bermuda or under license granted by the Minister of Finance. While an insurer is permitted to reinsure risks undertaken by any company incorporated in Bermuda and permitted to engage in the insurance and reinsurance business, generally it is not permitted without a special license granted by the Minister of Finance to insure Bermuda domestic risks or risks of persons of, in or based in Bermuda.

        ACGL and Arch Re Bermuda also need to comply with the provisions of the Companies Act regulating the payment of dividends and making distributions from contributed surplus. A company shall not declare or pay a dividend, or make a distribution out of contributed surplus, if there are reasonable grounds for believing that: (a) the company is, or would after the payment be, unable to pay its liabilities as they become due; or (b) the realizable value of the company's assets would thereby be less than the aggregate of its liabilities and its issued share capital and share premium accounts. See "Management's Discussion and Analysis of Financial Condition and Results of Operations—Liquidity and Capital Resources" and note 15, "Statutory Information," of the notes accompanying our financial statements.

        Under Bermuda law, only persons who are Bermudians, spouses of Bermudians, holders of a permanent resident's certificate or holders of a working resident's certificate ("exempted persons") may engage in gainful occupation in Bermuda without an appropriate governmental work permit. Our success may depend in part upon the continued services of key employees in Bermuda. Certain of our current key employees are not exempted persons and, as such, require specific approval to work for us in Bermuda. A work permit may be granted or extended upon showing that, after proper public advertisement, no exempted person is available who meets the minimum standards reasonably required by the employer. The Bermuda government has a policy that places a six-year term limit on individuals with work permits, subject to certain exemptions for key employees.

        General.    The Financial Services Authority (the "FSA") regulates insurance and reinsurance companies operating in the U.K. under the Financial Services and Markets Act 2000 (the "FSMA"), including Arch-Europe, our U.K.-based subsidiary. In May 2004, Arch-Europe was licensed and authorized by the FSA. It holds the relevant permissions for the classes of insurance business which it underwrites in the U.K. All U.K. companies are also subject to a range of statutory provisions, including the laws and regulations of the Companies Acts 1985 (as amended) (the "Companies Acts").

        The primary statutory goals of the FSA are to maintain and promote confidence in the U.K. financial system, secure the appropriate degree of protection for consumers and reduce financial crime. The FSA regulatory regime imposes risk management, solvency and capital requirements on U.K. insurance companies. The FSA has broad authority to supervise and regulate insurance companies which extends to enforcement of the provisions of the FSMA and intervention in the operations of an insurance company. The FSA regime is based on principles from which all of its rules and guidance derive. Among these principles, the FSA increasingly emphasizes a "culture of compliance" in those firms it regulates. The FSA carries out regular Advanced Risk Responsive Operating Framework ("ARROW") assessments of regulated firms to ensure that compliance with its rules and guidance. The FSA conducted a risk assessment of Arch-Europe in 2004 and in 2006, and will continue to do so again on a regular schedule. The assessment provided the FSA's views on Arch-Europe's risk profile and its regulatory capital requirements. In some cases, the FSA may require remedial action or adjustments to a company's management, operations, capital requirements, claims management or business plan. The FSA recently announced that greater focus will be placed on senior management arrangements, systems and controls, the fair treatment of clients and making further progress towards the development of enhanced risk-based minimum capital requirements for non life insurance companies, working together

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with the regulatory bodies of the Member States of the European Union ("EU") and the European Commission, which acts as the initiator of action and executive body of the EU.

        Financial Resources.    Arch-Europe is required to demonstrate to the FSA that it has adequate financial assets to meet the financial resources requirement for its category. On an annual basis, Arch-Europe is required to provide the FSA with its own risk-based assessment of its capital needs, taking into account comprehensive risk factors, including market, credit, operational, liquidity and group risks to generate a revised calculation of its expected liabilities which, in turn, enable the FSA to provide individual capital guidance to Arch-Europe. Arch-Europe's surplus is above the risk-based capital threshold allowed by the FSA's individual capital assessment of Arch-Europe. The FSA requires that Arch-Europe maintain a margin of solvency calculation based on the classes of business for which it is authorized and within its premium income projections applied to its worldwide general business.

        Reporting Requirements.    Like all U.K. companies, Arch-Europe must file and submit its annual audited financial statements and related reports to the Registrar of Companies under the Companies Acts together with an annual return of certain core corporate information and changes from the prior year. This requirement is in addition to the regulatory returns required to be filed annually with the FSA.

        Restrictions on Payment of Dividends.    Under U.K. law, all U.K. companies are restricted from declaring a dividend to their shareholders unless they have "profits available for distribution." The calculation as to whether a company has sufficient profits is based on its accumulated realized profits minus its accumulated realized losses. U.K. insurance regulatory laws do not prohibit the payment of dividends, but the FSA requires that insurance companies maintain certain solvency margins and may restrict the payment of a dividend by Arch-Europe. See "Management's Discussion and Analysis of Financial Condition and Results of Operations—Liquidity and Capital Resources" and note 15, "Statutory Information," of the notes accompanying our financial statements.

        European Union Considerations.    As a licensed insurance company in the U.K., a Member State of the EU, Arch-Europe's authorization as an insurer is recognized throughout the European Economic Area ("EEA"), subject only to certain notification and application requirements. This authorization enables Arch-Europe to establish a branch in any other Member State of the EU, where it will be subject to the insurance regulations of each such Member State with respect to the conduct of its business in such Member State, but remain subject only to the financial and operational supervision by the FSA. The framework for the establishment of branches in Member States of the EU other than the U.K. was generally set forth, and remains subject to, directives by the European Council, the legislative body of the EU, which directives are then implemented in each Member State. Arch-Europe currently has branches in Germany, Italy, Spain and Denmark, and may establish branches in other Member States of the EU in the future. Further, as an insurer in an EU Member State, Arch-Europe has the freedom to provide insurance services anywhere in the EEA subject to compliance with certain rules governing such provision, including notification to the FSA.

        The Canadian branch office of Arch Insurance is subject to federal, as well as provincial and territorial, regulation in Canada. The Office of the Superintendent of Financial Institutions ("OSFI") is the federal regulatory body that, under the Insurance Companies Act (Canada), regulates federal Canadian and non-Canadian insurance companies operating in Canada. The primary goal of OSFI is to supervise the safety and soundness of insurance companies with the aim of securing the appropriate level of protection of insureds by imposing risk management, solvency and capital requirements on such companies. In addition, the Canadian branch is subject to regulation in the provinces and territories in which it underwrites insurance, and the primary goal of insurance regulation at the provincial and territorial levels is to govern the market conduct of insurance companies. The Canadian branch is

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licensed to carry on insurance business by OSFI and in each province and territory, except for Prince Edward Island.

        In November 2006, Arch Re Bermuda opened a branch office in Zurich, Switzerland named Arch Reinsurance Ltd., Hamilton (Bermuda), European Branch Zurich. The activities of the Arch Re Swiss Branch are limited to reinsurance so it is not required to be licensed by the Swiss insurance regulatory authorities.

        The single system established in the EU for regulation and supervision of the general insurance sector and its single passport regime have until recently applied only to direct insurance, and there has been no common regulation of reinsurance in the EU. On December 9, 2005, the EU published the Reinsurance Directive (the "Directive") as a first step in harmonization of reinsurance regulation in the single market. Member States of the EU and the EEA were required to implement the Directive by December 2007. A number of Member States have implemented the Directive, but some have yet to pass the necessary legislation. Once fully implemented, pure reinsurers established in a Member State of the EU will have freedom to establish branches in and provide services to all EEA states similar to that enjoyed by direct insurers and they will be subject to similar rules in relation to licensing and financial supervision. At present, there are Member States in which this freedom does not apply. Arch-Europe, being established in the U.K. and authorized by the FSA to write reinsurance, is now able, subject to regulatory notifications and there being no objection from the FSA and the Member States concerned, to establish branches and provide reinsurance services in those EEA states which have implemented the Directive. The Directive itself does not prohibit EEA insurers from obtaining reinsurance from reinsurers licensed outside the EEA, such as Arch Re Bermuda. As such, Arch Re Bermuda may do business from Bermuda with EEA Member States but it may not directly operate its reinsurance business within the EEA. Unless agreement is reached between the European Commission and Bermuda to accord Bermuda-based reinsurers market access on the basis of the prudential nature of Bermuda regulation, each individual EEA Member State may impose conditions on reinsurance provided by Bermuda-based reinsurers which could restrict their future provision of reinsurance to the EEA Member State concerned. There are no indications as yet that any EEA Member State will take this course, but Hungary and the Slovak Republic have certain prohibitions on the purchase of insurance from reinsurers not authorized in the EEA. Also, a number of EEA Member States have introduced or are considering legislation that would limit the ability of Bermudian reinsurers to advertise or otherwise market their reinsurance services in those EEA Member States.

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TAX MATTERS

        The following summary of the taxation of ACGL and the taxation of our shareholders is based upon current law and is for general information only. Legislative, judicial or administrative changes may be forthcoming that could affect this summary.

        The following legal discussion (including and subject to the matters and qualifications set forth in such summary) of certain tax considerations (a) under "—Taxation of ACGL—Bermuda" and "—Taxation of Shareholders—Bermuda Taxation" is based upon the advice of Conyers Dill & Pearman, Hamilton, Bermuda and (b) under "—Taxation of ACGL—United States," "—Taxation of Shareholders—United States Taxation," "—Taxation of Our U.S. Shareholders" and "—United States Taxation of Non-U.S. Shareholders" is based upon the advice of Cahill Gordon & Reindel LLP, New York, New York (the advice of such firms does not include accounting matters, determinations or conclusions relating to the business or activities of ACGL). The summary is based upon current law and is for general information only. The tax treatment of a holder of our shares (common shares, series A non-cumulative preferred shares or series B non-cumulative preferred shares), or of a person treated as a holder of our shares for U.S. federal income, state, local or non-U.S. tax purposes, may vary depending on the holder's particular tax situation. Legislative, judicial or administrative changes or interpretations may be forthcoming that could be retroactive and could affect the tax consequences to us or to holders of our shares.

Taxation of ACGL

        Under current Bermuda law, ACGL is not subject to tax on income or capital gains. ACGL has obtained from the Minister of Finance under the Exempted Undertakings Tax Protection Act 1966 an assurance that, in the event that Bermuda enacts legislation imposing tax computed on profits, income, any capital asset, gain or appreciation, or any tax in the nature of estate duty or inheritance, the imposition of any such tax shall not be applicable to ACGL or to any of our operations or our shares, debentures or other obligations until March 28, 2016. We could be subject to taxes in Bermuda after that date. This assurance will be subject to the proviso that it is not to be construed so as to prevent the application of any tax or duty to such persons as are ordinarily resident in Bermuda (we are not so currently affected) or to prevent the application of any tax payable in accordance with the provisions of the Land Tax Act 1967 or otherwise payable in relation to any property leased to us or our insurance subsidiary. We pay annual Bermuda government fees, and our Bermuda insurance and reinsurance subsidiary pays annual insurance license fees. In addition, all entities employing individuals in Bermuda are required to pay a payroll tax and other sundry taxes payable, directly or indirectly, to the Bermuda government.

        ACGL and its non-U.S. subsidiaries intend to conduct their operations in a manner that will not cause them to be treated as engaged in a trade or business in the United States and, therefore, will not be required to pay U.S. federal income taxes (other than U.S. excise taxes on insurance and reinsurance premium and withholding taxes on dividends and certain other U.S. source investment income). However, because definitive identification of activities which constitute being engaged in a trade or business in the U.S. is not provided by the Internal Revenue Code of 1986, as amended (the "Code"), or regulations or court decisions, there can be no assurance that the U.S. Internal Revenue Service will not contend successfully that ACGL or its non-U.S. subsidiaries are or have been engaged in a trade or business in the United States. A foreign corporation deemed to be so engaged would be subject to U.S. income tax, as well as the branch profits tax, on its income, which is treated as effectively connected with the conduct of that trade or business unless the corporation is entitled to

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relief under the permanent establishment provisions of a tax treaty. Such income tax, if imposed, would be based on effectively connected income computed in a manner generally analogous to that applied to the income of a domestic corporation, except that deductions and credits generally are not permitted unless the foreign corporation has timely filed a U.S. federal income tax return in accordance with applicable regulations. Penalties may be assessed for failure to file tax returns. The 30% branch profits tax is imposed on net income after subtracting the regular corporate tax and making certain other adjustments.

        Under the income tax treaty between Bermuda and the United States (the "Treaty"), ACGL's Bermuda insurance subsidiaries will be subject to U.S. income tax on any insurance premium income found to be effectively connected with a U.S. trade or business only if that trade or business is conducted through a permanent establishment in the United States. No regulations interpreting the Treaty have been issued. While there can be no assurances, ACGL does not believe that any of its Bermuda insurance subsidiaries has a permanent establishment in the United States. Such subsidiaries would not be entitled to the benefits of the Treaty if (i) less than 50% of ACGL's shares were beneficially owned, directly or indirectly, by Bermuda residents or U.S. citizens or residents, or (ii) any such subsidiary's income were used in substantial part to make disproportionate distributions to, or to meet certain liabilities to, persons who are not Bermuda residents or U.S. citizens or residents. While there can be no assurances, ACGL believes that its Bermuda insurance subsidiaries are eligible for Treaty benefits.

        The Treaty clearly applies to premium income, but may be construed as not protecting investment income. If ACGL's Bermuda insurance subsidiaries were considered to be engaged in a U.S. trade or business and were entitled to the benefits of the Treaty in general, but the Treaty were not found to protect investment income, a portion of such subsidiaries' investment income could be subject to U.S. federal income tax.

        Non-U.S. insurance companies carrying on an insurance business within the United States have a certain minimum amount of effectively connected net investment income, determined in accordance with a formula that depends, in part, on the amount of U.S. risk insured or reinsured by such companies. If any of ACGL's non-U.S. insurance subsidiaries is considered to be engaged in the conduct of an insurance business in the United States, a significant portion of such company's investment income could be subject to U.S. income tax.

        Non-U.S. corporations not engaged in a trade or business in the United States are nonetheless subject to U.S. income tax on certain "fixed or determinable annual or periodic gains, profits and income" derived from sources within the United States as enumerated in Section 881(a) of the Code (such as dividends and certain interest on investments), subject to exemption under the Code or reduction by applicable treaties.

        The United States also imposes an excise tax on insurance and reinsurance premiums paid to non-U.S. insurers or reinsurers with respect to risks located in the United States. The rates of tax, unless reduced by an applicable U.S. tax treaty, are 4% for non-life insurance premiums and 1% for life insurance and all reinsurance premiums.

        Personal Holding Company Rules.    A domestic corporation will not be classified as a personal holding company (a "PHC") in a given taxable year unless both (i) at some time during the last half of such taxable year, five or fewer individuals (without regard to their citizenship or residency) own or are deemed to own (pursuant to certain constructive ownership rules) more than 50% of the corporation's shares by value, and (ii) at least 60% of the adjusted ordinary gross income of the corporation for such taxable year consists of PHC income (as defined in Section 543 of the Code). For purposes of the 50% share ownership test, all of our shares owned by an investment partnership will be attributed to each of its partners, if any, who are individuals. As a result of this attribution rule, we believe that currently five or fewer individuals may be treated as owning more than 50% of the value of our shares.

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Consequently, one or more of our domestic subsidiaries could be or become PHCs, depending on whether any of our subsidiaries satisfy the PHC gross income test.

        We will use commercially reasonable efforts to cause each of our domestic subsidiaries not to satisfy the gross income requirement set forth in Section 542(a) of the Code. If, however, any of our domestic subsidiaries is or were to become a PHC in a given taxable year, such company would be subject to PHC tax (at a 15% rate for taxable years before January 1, 2011, and thereafter at the highest marginal rate on ordinary income applicable to individuals) on its "undistributed PHC income." PHC income generally would not include underwriting income. If any of our subsidiaries is or becomes a PHC, there can be no assurance that the amount of PHC income would be immaterial.

        Certain of our U.S. subsidiaries have been PHCs. Such subsidiaries did not have "undistributed personal holding company income" and do not expect to have "undistributed personal holding company income" in 2007.

        There can be no assurance that each of our domestic subsidiaries is not or will not become a PHC in the future because of factors including factual uncertainties regarding the application of the PHC rules, the makeup of our shareholder base and other circumstances that affect the application of the PHC rules to our domestic subsidiaries.

        Our European subsidiaries, Arch-Europe and Arch Capital U.K. Ltd. ("Arch-U.K."), are companies incorporated in the U.K. and are therefore resident in the U.K. for corporation tax purposes and will be subject to U.K. corporate tax on their respective worldwide profits. The current rate of U.K. corporation tax is generally 30% on profits, but this is scheduled to be reduced to 28% for profits accruing from April 1, 2008.

        In January 2005, Arch Insurance received its federal license to commence underwriting in Canada and began writing business in the first quarter of 2005 through its branch operation. The branch operation is taxed on net business income earned in Canada. The general federal corporate income tax rate in Canada is currently 19.5%. The general federal corporate income tax rate in Canada is legislated to be reduced to 19.0% in 2009, 18.0% in 2010, 16.5% in 2011 and, finally, 15.0% in 2012. Provincial and territorial corporate income tax rates are added to the general federal corporate income tax rate and generally vary between 9.9% and 16.0%. Canadian income taxes are also creditable to the Company's U.S. operations.

        Arch Re Swiss Branch, established as a branch office of Arch Re Bermuda, is subject to Swiss corporation tax on the profit which is allocated to the branch. Under a mixed company ruling, the effective tax rate is expected to be between 11.4% and 12.6%. The annual capital tax on the equity which is allocated to Arch Re Swiss Branch is approximately .035%.

        Arch Re Denmark, established as a subsidiary of Arch Re Bermuda, is subject to Danish corporation taxes on its profits at a rate of 28%.

Taxation of Shareholders

        The following summary sets forth certain United States federal income tax considerations related to the purchase, ownership and disposition of our common shares and our series A non-cumulative

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preferred shares and our series B non-cumulative preferred shares (collectively referred to as the "preferred shares"). Unless otherwise stated, this summary deals only with shareholders ("U.S. Holders") that are United States Persons (as defined below) who hold their common shares and preferred shares as capital assets and as beneficial owners. The following discussion is only a general summary of the United States federal income tax matters described herein and does not purport to address all of the United States federal income tax consequences that may be relevant to a particular shareholder in light of such shareholder's specific circumstances. In addition, the following summary does not describe the United States federal income tax consequences that may be relevant to certain types of shareholders, such as banks, insurance companies, regulated investment companies, real estate investment trusts, financial asset securitization investment trusts, dealers in securities or traders that adopt a mark-to-market method of tax accounting, tax exempt organizations, expatriates or persons who hold the common shares or preferred shares as part of a hedging or conversion transaction or as part of a straddle, who may be subject to special rules or treatment under the Code. This discussion is based upon the Code, the Treasury regulations promulgated thereunder and any relevant administrative rulings or pronouncements or judicial decisions, all as in effect on the date of this annual report and as currently interpreted, and does not take into account possible changes in such tax laws or interpretations thereof, which may apply retroactively. This discussion does not include any description of the tax laws of any state or local governments within the United States, or of any foreign government, that may be applicable to our common shares or preferred shares or the shareholders. Persons considering making an investment in the common shares or preferred shares should consult their own tax advisors concerning the application of the United States federal tax laws to their particular situations as well as any tax consequences arising under the laws of any state, local or foreign taxing jurisdiction prior to making such investment.

        If a partnership holds our common shares or preferred shares, the tax treatment of a partner will generally depend upon the status of the partner and the activities of the partnership. If you are a partner of a partnership holding our common shares or preferred shares, you should consult your tax advisor.

        For purposes of this discussion, the term "United States Person" means:

        Currently, there is no Bermuda withholding tax on dividends paid by us.

        Taxation of Dividends.    The preferred shares should be properly classified as equity rather than debt for U.S. federal income tax purposes. Subject to the discussions below relating to the potential

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application of the CFC and PFIC rules, as defined below, cash distributions, if any, made with respect to our common shares or preferred shares will constitute dividends for U.S. federal income tax purposes to the extent paid out of our current or accumulated earnings and profits (as computed using U.S. tax principles). If a U.S. Holder of our common shares or our preferred shares is an individual or other non-corporate holder, dividends paid, if any, to that holder in taxable years beginning before January 1, 2011 that constitute qualified dividend income will be taxable at the rate applicable for long-term capital gains (generally up to 15%), provided that such person meets a holding period requirement. Generally in order to meet the holding period requirement, the United States Person must hold the common shares for more than 60 days during the 121-day period beginning 60 days before the ex-dividend date and must hold preferred shares for more than 90 days during the 181-day period beginning 90 days before the ex-dividend date. Dividends paid, if any, with respect to common shares or preferred shares generally will be qualified dividend income, provided the common shares or preferred shares are readily tradable on an established securities market in the U.S. in the year in which the shareholder receives the dividend (which should be the case for shares that are listed on the NASDAQ Stock Market or the New York Stock Exchange) and ACGL is not considered to be a passive foreign investment company in either the year of the distribution or the preceding taxable year. No assurance can be given that the preferred shares will be considered readily tradable on an established securities market in the United States. See "—Taxation of Our U.S. Shareholders" below. After December 31, 2010, qualified dividend income will no longer be taxed at the rate applicable for long-term capital gains unless Congress enacts legislation providing otherwise.

        Distributions with respect to the common shares and the preferred shares will not be eligible for the dividends-received deduction allowed to U.S. corporations under the Code. To the extent distributions on our common shares and preferred shares exceed our earnings and profits, they will be treated first as a return of the U.S. Holder's basis in our common shares and our preferred shares to the extent thereof, and then as gain from the sale of a capital asset.

        Sale, Exchange or Other Disposition.    Subject to the discussions below relating to the potential application of the CFC and PFIC rules, holders of common shares and preferred shares generally will recognize capital gain or loss for U.S. federal income tax purposes on the sale, exchange or disposition of common shares or preferred shares, as applicable.

        Redemption of Preferred Shares.    A redemption of the preferred shares will be treated under section 302 of the Code as a dividend if we have sufficient earnings and profits, unless the redemption satisfies one of the tests set forth in section 302(b) of the Code enabling the redemption to be treated as a sale or exchange, subject to the discussion herein relating to the potential application of the CFC, RPII and PFIC rules. Under the relevant Code section 302(b) tests, the redemption should be treated as a sale or exchange only if it (1) is substantially disproportionate, (2) constitutes a complete termination of the holder's stock interest in us or (3) is "not essentially equivalent to a dividend." In determining whether any of these tests are met, shares considered to be owned by the holder by reason of certain constructive ownership rules set forth in the Code, as well as shares actually owned, must generally be taken into account. It may be more difficult for a United States Person who owns, actually or constructively by operation of the attribution rules, any of our other shares to satisfy any of the above requirements. The determination as to whether any of the alternative tests of section 302(b) of the Code is satisfied with respect to a particular holder of the preference shares depends on the facts and circumstances as of the time the determination is made.

Taxation of Our U.S. Shareholders

        Under our bye-laws, the 9.9% voting restriction applicable to the Controlled Shares of a U.S. Person (as defined in our bye-laws) generally does not apply to certain of our investors. As a result of

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certain attribution rules, we believe, therefore, that we and our foreign subsidiaries might be controlled foreign corporations ("CFCs"). That status as a CFC would not cause us or any of our subsidiaries to be subject to U.S. federal income tax. Such status also would have no adverse U.S. federal income tax consequences for any U.S. Holder that is considered to own less than 10% of the total combined voting power of our shares or those of our foreign subsidiaries. Only U.S. Holders that are considered to own 10% or more of the total combined voting power of our shares or those of our foreign subsidiaries (taking into account shares actually owned by such U.S. Holder as well as shares attributed to such U.S. Holder under the Code or the regulations thereunder) (a "10% U.S. Voting Shareholder") would be affected by our status as a CFC. The preferred shares generally should not be considered voting stock for purposes of determining whether a United States Person would be a "10% U.S. Voting Shareholder." The shares may, however, become entitled to vote (as a class along with any other class of preferred shares of ACGL then outstanding) for the election of two additional members of the board of directors of ACGL if ACGL does not declare and pay dividends for the equivalent of six or more dividend periods. In such case, the preferred shares should be treated as voting stock for as long as such voting rights continue. Our bye-laws are intended to prevent any U.S. Holder from being considered a 10% U.S. Voting Shareholder by limiting the votes conferred by the Controlled Shares (as defined in our bye-laws) of any U.S. Person to 9.9% of the total voting power of all our shares entitled to vote. However, because under our bye-laws certain funds associated with Warburg Pincus and Hellman & Friedman generally are entitled to vote their directly owned common shares in full, a U.S. Holder that is attributed (under the Code or the regulations thereunder) common shares owned by such funds may be considered a 10% U.S. Voting Shareholder. If you are a direct or indirect investor in a fund associated with Warburg Pincus or Hellman & Friedman, additional common shares could be attributed to you for purposes of determining whether you are considered to be a 10% U.S. Voting Shareholder. If we are a CFC, a U.S. Holder that is considered a 10% U.S. Voting Shareholder would be subject to current U.S. federal income taxation (at ordinary income tax rates) to the extent of all or a portion of the undistributed earnings and profits of ACGL and our subsidiaries attributable to "subpart F income" (including certain insurance premium income and investment income) and may be taxable at ordinary income tax rates on any gain realized on a sale or other disposition (including by way of repurchase or liquidation) of our shares to the extent of the current and accumulated earnings and profits attributable to such shares.

        While our bye-laws are intended to prevent any member from being considered a 10% U.S. Voting Shareholder (except as described above), there can be no assurance that a U.S. Holder will not be treated as a 10% U.S. Voting Shareholder, by attribution or otherwise, under the Code or any applicable regulations thereunder. See "Risk Factors—Risks Relating to Taxation—U.S. persons who hold our common shares or preferred shares may be subject to U.S. income taxation at ordinary income rates on our undistributed earnings and profits."

        Generally, we do not expect the gross "related person insurance income" ("RPII") of any of our non-U.S. subsidiaries to equal or exceed 20% of its gross insurance income in any taxable year for the foreseeable future and do not expect the direct or indirect insureds (and related persons) of any such subsidiary to directly or indirectly own 20% or more of either the voting power or value of our stock. Consequently, we do not expect any U.S. person owning common shares or preferred shares to be required to include in gross income for U.S. federal income tax purposes RPII income, but there can be no assurance that this will be the case.

        Section 953(c)(7) of the Code generally provides that Section 1248 of the Code (which generally would require a U.S. Holder to treat certain gains attributable to the sale, exchange or disposition of common shares or preferred shares as a dividend) will apply to the sale or exchange by a U.S. shareholder of shares in a foreign corporation that is characterized as a CFC under the RPII rules if

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the foreign corporation would be taxed as an insurance company if it were a domestic corporation, regardless of whether the U.S. shareholder is a 10% U.S. Voting Shareholder or whether the corporation qualifies for either the RPII 20% ownership exception or the RPII 20% gross income exception. Although existing Treasury Department regulations do not address the question, proposed Treasury regulations issued in April 1991 create some ambiguity as to whether Section 1248 and the requirement to file Form 5471 would apply when the foreign corporation has a foreign insurance subsidiary that is a CFC for RPII purposes and that would be taxed as an insurance company if it were a domestic corporation. We believe that Section 1248 and the requirement to file Form 5471 will not apply to a less than 10% U.S. Shareholder because ACGL is not directly engaged in the insurance business. There can be no assurance, however, that the U.S. Internal Revenue Service will interpret the proposed regulations in this manner or that the Treasury Department will not take the position that Section 1248 and the requirement to file Form 5471 will apply to dispositions of our common shares or our preferred shares.

        If the U.S. Internal Revenue Service or U.S. Treasury Department were to make Section 1248 and the Form 5471 filing requirement applicable to the sale of our shares, we would notify shareholders that Section 1248 of the Code and the requirement to file Form 5471 will apply to dispositions of our shares. Thereafter, we would send a notice after the end of each calendar year to all persons who were shareholders during the year notifying them that Section 1248 and the requirement to file Form 5471 apply to dispositions of our shares by U.S. Holders. We would attach to this notice a copy of Form 5471 completed with all our information and instructions for completing the shareholder information.

        Tax-exempt entities may be required to treat certain Subpart F insurance income, including RPII, that is includible in income by the tax-exempt entity as unrelated business taxable income. Prospective investors that are tax exempt entities are urged to consult their tax advisors as to the potential impact of the unrelated business taxable income provisions of the Code.

        Sections 1291 through 1298 of the Code contain special rules applicable with respect to foreign corporations that are "passive foreign investment companies" ("PFICs"). In general, a foreign corporation will be a PFIC if 75% or more of its income constitutes "passive income" or 50% or more of its assets produce passive income. If we were to be characterized as a PFIC, U.S. Holders would be subject to a penalty tax at the time of their sale of (or receipt of an "excess distribution" with respect to) their common shares or preferred shares. In general, a shareholder receives an "excess distribution" if the amount of the distribution is more than 125% of the average distribution with respect to the shares during the three preceding taxable years (or shorter period during which the taxpayer held the stock). In general, the penalty tax is equivalent to an interest charge on taxes that are deemed due during the period the shareholder owned the shares, computed by assuming that the excess distribution or gain (in the case of a sale) with respect to the shares was taxable in equal portions throughout the holder's period of ownership. The interest charge is equal to the applicable rate imposed on underpayments of U.S. federal income tax for such period. A U.S. shareholder may avoid some of the adverse tax consequences of owning shares in a PFIC by making a qualified electing fund ("QEF") election. A QEF election is revocable only with the consent of the IRS and has the following consequences to a shareholder:

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        The PFIC statutory provisions contain an express exception for income "derived in the active conduct of an insurance business by a corporation which is predominantly engaged in an insurance business..." This exception is intended to ensure that income derived by a bona fide insurance company is not treated as passive income, except to the extent such income is attributable to financial reserves in excess of the reasonable needs of the insurance business. The PFIC statutory provisions contain a look-through rule that states that, for purposes of determining whether a foreign corporation is a PFIC, such foreign corporation shall be treated as if it "received directly its proportionate share of the income" and as if it "held its proportionate share of the assets" of any other corporation in which it owns at least 25% of the stock. We believe that we are not a PFIC, and we will use reasonable best efforts to cause us and each of our non-U.S. insurance subsidiaries not to constitute a PFIC.

        No regulations interpreting the substantive PFIC provisions have yet been issued. Each U.S. Holder should consult his tax advisor as to the effects of these rules.

United States Taxation of Non-U.S. Shareholders

        Cash distributions, if any, made with respect to common shares or preferred shares held by shareholders who are not United States Persons ("Non-U.S. holders") generally will not be subject to United States withholding tax.

        Non-U.S. holders of common shares or preferred shares generally will not be subject to U.S. federal income tax with respect to gain realized upon the sale, exchange or other disposition of such shares unless such gain is effectively connected with a U.S. trade or business of the Non-U.S. holder in the United States or such person is present in the United States for 183 days or more in the taxable year the gain is realized and certain other requirements are satisfied.

        Non-U.S. holders of common shares or preferred shares will not be subject to U.S. information reporting or backup withholding with respect to dispositions of common shares effected through a non-U.S. office of a broker, unless the broker has certain connections to the United States or is a United States person. No U.S. backup withholding will apply to payments of dividends, if any, on our common shares or our preferred shares.

        Shareholders should consult their own tax advisors with respect to the applicability to them of the tax laws of other jurisdictions.

ITEM 1A.    RISK FACTORS

        Set forth below are risk factors relating to our business. You should also refer to the other information provided in this report, including our "Management's Discussion and Analysis of Financial Condition and Results of Operations" and our accompanying consolidated financial statements, as well as the information under the heading "Cautionary Note Regarding Forward-Looking Statements."

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Risks Relating to Our Industry

We operate in a highly competitive environment, and we may not be able to compete successfully in our industry.

        The insurance and reinsurance industry is highly competitive. We compete with major U.S. and non-U.S. insurers and reinsurers, many of which have greater financial, marketing and management resources than we do, as well as other potential providers of capital willing to assume insurance and/or reinsurance risk. We also compete with new companies that continue to be formed to enter the insurance and reinsurance markets. In our insurance business, we compete with insurers that provide specialty property and casualty lines of insurance, including ACE Limited, Allied World Assurance Company, Ltd., American International Group, Inc., AXIS Capital Holdings Limited, Berkshire Hathaway, Inc., Chubb Corporation, Endurance Specialty Holdings Ltd., The Hartford Financial Services Group, Inc., HCC Insurance Holdings, Inc., Lloyd's of London, The St. Paul Travelers Companies, W.R. Berkley Corp., XL Capital Ltd. and Zurich Insurance Group. In our reinsurance business, we compete with reinsurers that provide property and casualty lines of reinsurance, including ACE Limited, AXIS Capital Holdings Limited, Berkshire Hathaway, Inc., Endurance Specialty Holdings Ltd., Everest Re Group Ltd., Hannover Rückversicherung AG, Lloyd's of London, Montpelier Re Holdings Ltd., Munich Re Group, PartnerRe Ltd., Platinum Underwriters Holdings, Ltd., RenaissanceRe Holdings Ltd., Swiss Reinsurance Company, Transatlantic Holdings, Inc. and XL Capital Ltd. We do not believe that we have a significant market share in any of our markets.

        Financial institutions and other capital markets participants also offer alternative products and services similar to our own or alternative products that compete with insurance and reinsurance products. In addition, we may not be aware of other companies that may be planning to enter the segments of the insurance and reinsurance market in which we operate.

        Our competitive position is based on many factors, including our perceived overall financial strength, ratings assigned by independent rating agencies, geographic scope of business, client relationships, premiums charged, contract terms and conditions, products and services offered (including the ability to design customized programs), speed of claims payment, reputation, experience and qualifications of employees and local presence. We may not be successful in competing with others on any of these bases, and the intensity of competition in our industry may erode profitability and result in less favorable policy terms and conditions for insurance and reinsurance companies generally, including us.

The insurance and reinsurance industry is highly cyclical, and we expect to continue to experience periods characterized by excess underwriting capacity and unfavorable premium rates.

        Historically, insurers and reinsurers have experienced significant fluctuations in operating results due to competition, frequency of occurrence or severity of catastrophic events, levels of capacity, general economic conditions, changes in legislation, case law and prevailing concepts of liability and other factors. In particular, demand for reinsurance is influenced significantly by the underwriting results of primary insurers and prevailing general economic conditions. The supply of insurance and reinsurance is related to prevailing prices and levels of surplus capacity that, in turn, may fluctuate in response to changes in rates of return being realized in the insurance and reinsurance industry. As a result, the insurance and reinsurance business historically has been a cyclical industry characterized by periods of intense price competition due to excessive underwriting capacity as well as periods when shortages of capacity permitted favorable premium levels and changes in terms and conditions. The supply of insurance and reinsurance has increased over the past several years and may increase further, either as a result of capital provided by new entrants or by the commitment of additional capital by existing insurers or reinsurers. Continued increases in the supply of insurance and reinsurance may

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have consequences for us, including fewer contracts written, lower premium rates, increased expenses for customer acquisition and retention, and less favorable policy terms and conditions.

We could face unanticipated losses from war, terrorism and political instability, and these or other unanticipated losses could have a material adverse effect on our financial condition and results of operations.

        We have substantial exposure to unexpected, large losses resulting from future man-made catastrophic events, such as acts of war, acts of terrorism and political instability. These risks are inherently unpredictable, although recent events may lead to increased frequency and severity of losses. It is difficult to predict the timing of such events with statistical certainty or estimate the amount of loss any given occurrence will generate. In certain instances, we specifically insure and reinsure risks resulting from acts of terrorism. Even in cases where we attempt to exclude losses from terrorism and certain other similar risks from some coverages written by us, we may not be successful in doing so. Moreover, irrespective of the clarity and inclusiveness of policy language, there can be no assurance that a court or arbitration panel will not limit enforceability of policy language or otherwise issue a ruling adverse to us. Accordingly, while we believe our reinsurance programs, together with the coverage provided under TRIPRA, are sufficient to reasonably limit our net losses relating to potential future terrorist attacks, we can offer no assurance that our available capital will be adequate to cover losses when they materialize. To the extent that an act of terrorism is certified by the Secretary of the Treasury, our U.S. insurance operations may be covered under TRIPRA for up to 85% of its losses for 2007 and future years, in each case subject to a mandatory deductible of 20% for 2007 through 2014. If an act (or acts) of terrorism result in covered losses exceeding the $100 billion annual limit, insurers with losses exceeding their deductibles will not be responsible for additional losses. It is not possible to completely eliminate our exposure to unforecasted or unpredictable events, and to the extent that losses from such risks occur, our financial condition and results of operations could be materially adversely affected.

The insurance and reinsurance industry is subject to regulatory and legislative initiatives or proposals from time to time which could adversely affect our business.

        From time to time, various regulatory and legislative changes have been proposed in the insurance and reinsurance industry. Among the proposals that have in the past been or are at present being considered are the possible introduction of federal regulation in addition to, or in lieu of, the current system of state regulation of insurers. There are a variety of proposals being considered by various state legislatures. We are unable to predict whether any of these laws and regulations will be adopted, the form in which any such laws and regulations would be adopted, or the effect, if any, these developments would have on our operations and financial condition.

Claims for catastrophic events could cause large losses and substantial volatility in our results of operations, and, as a result, the value of our securities, including our common shares and preferred shares, may fluctuate widely, and could have a material adverse effect on our financial position and results of operations.

        We have large aggregate exposures to natural disasters. Catastrophes can be caused by various events, including hurricanes, floods, windstorms, earthquakes, hailstorms, tornados, explosions, severe winter weather, fires and other natural disasters. Catastrophes can also cause losses in non-property business such as workers' compensation or general liability. In addition to the nature of the property business, we believe that economic and geographic trends affecting insured property, including inflation, property value appreciation and geographic concentration tend to generally increase the size of losses from catastrophic events over time. Our actual losses from catastrophic events which may occur, may vary materially from our current estimates due to the inherent uncertainties in making such determinations resulting from several factors, including the potential inaccuracies and inadequacies in

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the data provided by clients, brokers and ceding companies, the modeling techniques and the application of such techniques, the contingent nature of business interruption exposures, the effects of any resultant demand surge on claims activity and attendant coverage issues.

        The weather-related catastrophic events that occurred in the second half of 2005 caused significant industry losses, resulted in a substantial improvement in market conditions in property and certain marine lines of business and slowed declines in premium rates in other lines. However, during 2006 and 2007, price erosion occurred in many lines of business as a result of competitive pressures in the insurance market. We increased our writings in property and certain marine lines of business and these lines represented a larger proportion of our overall book of business in 2006 and 2007 than in prior periods. We expect that our writings in these lines of business will continue to represent a significant proportion of our overall book of business in future periods and may represent a larger proportion of our overall book of business in future periods, which could increase the volatility of our results of operations.

        In addition, over the past several years, changing weather patterns and climatic conditions, such as global warming, have added to the unpredictability and frequency of natural disasters in certain parts of the world and created additional uncertainty as to future trends and exposures. Claims for catastrophic events could expose us to large losses and cause substantial volatility in our results of operations, which could cause the value of our securities, including our common shares and preferred shares, to fluctuate widely.

Underwriting claims and reserving for losses are based on probabilities and related modeling, which are subject to inherent uncertainties.

        Our success is dependent upon our ability to assess accurately the risks associated with the businesses that we insure and reinsure. We establish reserves for losses and loss adjustment expenses which represent estimates involving actuarial and statistical projections, at a given point in time, of our expectations of the ultimate settlement and administration costs of losses incurred. We utilize actuarial models as well as available historical insurance industry loss ratio experience and loss development patterns to assist in the establishment of loss reserves. Actual losses and loss adjustment expenses paid will deviate, perhaps substantially, from the reserve estimates reflected in our financial statements.

        If our loss reserves are determined to be inadequate, we will be required to increase loss reserves at the time of such determination with a corresponding reduction in our net income in the period in which the deficiency becomes known. It is possible that claims in respect of events that have occurred could exceed our claim reserves and have a material adverse effect on our results of operations, in a particular period, or our financial condition in general. As a compounding factor, although most insurance contracts have policy limits, the nature of property and casualty insurance and reinsurance is such that losses can exceed policy limits for a variety of reasons and could significantly exceed the premiums received on the underlying policies, thereby further adversely affecting our financial condition.

        As of December 31, 2007, our reserves for unpaid losses and loss adjustment expenses, net of unpaid losses and loss adjustment expenses recoverable, were approximately $5.48 billion. Such reserves were established in accordance with applicable insurance laws and GAAP. Loss reserves are inherently subject to uncertainty. In establishing the reserves for losses and loss adjustment expenses, we have made various assumptions relating to the pricing of our reinsurance contracts and insurance policies and have also considered available historical industry experience and current industry conditions. Any estimates and assumptions made as part of the reserving process could prove to be inaccurate due to several factors, including the fact that limited historical information has been reported to us through December 31, 2007.

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The failure of any of the loss limitation methods we employ could have a material adverse effect on our financial condition or results of operations.

        We have large aggregate exposures to natural and man-made catastrophic events. Catastrophes can be caused by various events, including, but not limited to, hurricanes, floods, windstorms, earthquakes, hailstorms, explosions, severe winter weather and fires. Catastrophes can also cause losses in non-property business such as workers' compensation or general liability. In addition to the nature of property business, we believe that economic and geographic trends affecting insured property, including inflation, property value appreciation and geographic concentration, tend to generally increase the size of losses from catastrophic events over time.

        We have substantial exposure to unexpected, large losses resulting from future man-made catastrophic events, such as acts of war, acts of terrorism and political instability. These risks are inherently unpredictable and recent events may lead to increased frequency and severity of losses. It is difficult to predict the timing of such events with statistical certainty or estimate the amount of loss any given occurrence will generate. It is not possible to completely eliminate our exposure to unforecasted or unpredictable events and, to the extent that losses from such risks occur, our financial condition and results of operations could be materially adversely affected. Therefore, claims for natural and man-made catastrophic events could expose us to large losses and cause substantial volatility in our results of operations, which could cause the value of our common shares to fluctuate widely. In certain instances, we specifically insure and reinsure risks resulting from terrorism. Even in cases where we attempt to exclude losses from terrorism and certain other similar risks from some coverages written by us, we may not be successful in doing so. Moreover, irrespective of the clarity and inclusiveness of policy language, there can be no assurance that a court or arbitration panel will limit enforceability of policy language or otherwise issue a ruling adverse to us.

        We seek to limit our loss exposure by writing a number of our reinsurance contracts on an excess of loss basis, adhering to maximum limitations on reinsurance written in defined geographical zones, limiting program size for each client and prudent underwriting of each program written. In the case of proportional treaties, we may seek per occurrence limitations or loss ratio caps to limit the impact of losses from any one or series of events. In our insurance operations, we seek to limit our exposure through the purchase of reinsurance. We cannot be certain that any of these loss limitation methods will be effective. We also seek to limit our loss exposure by geographic diversification. Geographic zone limitations involve significant underwriting judgments, including the determination of the area of the zones and the inclusion of a particular policy within a particular zone's limits. There can be no assurance that various provisions of our policies, such as limitations or exclusions from coverage or choice of forum, will be enforceable in the manner we intend. Disputes relating to coverage and choice of legal forum may also arise. Underwriting is inherently a matter of judgment, involving important assumptions about matters that are inherently unpredictable and beyond our control, and for which historical experience and probability analysis may not provide sufficient guidance. One or more catastrophic or other events could result in claims that substantially exceed our expectations, which could have a material adverse effect on our financial condition or our results of operations, possibly to the extent of eliminating our shareholders' equity.

        For our natural catastrophe exposed business, we seek to limit the amount of exposure we will assume from any one insured or reinsured and the amount of the exposure to catastrophe losses from a single event in any geographic zone. We monitor our exposure to catastrophic events, including earthquake and wind, and periodically reevaluate the estimated probable maximum pre-tax loss for such exposures. Our estimated probable maximum pre-tax loss is determined through the use of modeling techniques, but such estimate does not represent our total potential loss for such exposures. We seek to limit the probable maximum pre-tax loss to a specific level for severe catastrophic events. Currently, we generally seek to limit the probable maximum pre-tax loss to approximately 25% of total

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shareholders' equity for a severe catastrophic event in any geographic zone that could be expected to occur once in every 250 years, although we reserve the right to change this threshold at any time. There can be no assurances that we will not suffer pre-tax losses greater than 25% of our total shareholders' equity from one or more catastrophic events due to several factors, including the inherent uncertainties in estimating the frequency and severity of such events and the margin of error in making such determinations resulting from potential inaccuracies and inadequacies in the data provided by clients and brokers, the modeling techniques and the application of such techniques or as a result of a decision to change the percentage of shareholders' equity exposed to a single catastrophic event. In addition, depending on business opportunities and the mix of business that may comprise our insurance and reinsurance portfolio, we may seek to adjust our self-imposed limitations on probable maximum pre-tax loss for catastrophe exposed business.

The risk associated with reinsurance underwriting could adversely affect us, and while reinsurance and retrocessional coverage will be used to limit our exposure to risks, the availability of such arrangements may be limited, and counterparty credit and other risks associated with our reinsurance arrangements may result in losses which could adversely affect our financial condition and results of operations.

        Like other reinsurers, our reinsurance group does not separately evaluate each of the individual risks assumed under reinsurance treaties. Therefore, we are largely dependent on the original underwriting decisions made by ceding companies. We are subject to the risk that the ceding companies may not have adequately evaluated the risks to be reinsured and that the premiums ceded may not adequately compensate us for the risks we assume.

        For the purposes of managing risk, we use reinsurance and also may use retrocessional arrangements. In the normal course of business, our insurance subsidiaries cede a substantial portion of their premiums through pro rata, excess of loss and facultative reinsurance agreements. Our reinsurance subsidiaries purchase a limited amount of retrocessional coverage as part of their aggregate risk management program. In addition, our reinsurance subsidiaries participate in "common account" retrocessional arrangements for certain pro rata treaties. Such arrangements reduce the effect of individual or aggregate losses to all companies participating on such treaties, including the reinsurers, such as our reinsurance subsidiaries, and the ceding company. For 2007, ceded premiums written represented approximately 29.9% of gross premiums written, compared to 29.5% and 21.8%, respectively, for 2006 and 2005.

        The availability and cost of reinsurance and retrocessional protection is subject to market conditions, which are beyond our control. As a result of such market conditions and other factors, we may not be able to successfully mitigate risk through reinsurance and retrocessional arrangements. Further, we are subject to credit risk with respect to our reinsurance and retrocessions because the ceding of risk to reinsurers and retrocessionaires does not relieve us of our liability to the clients or companies we insure or reinsure. Our losses for a given event or occurrence may increase if our reinsurers or retrocessionaires dispute or fail to meet their obligations to us or the reinsurance or retrocessional protections purchased by us are exhausted or are otherwise unavailable for any reason. Our failure to establish adequate reinsurance or retrocessional arrangements or the failure of our existing reinsurance or retrocessional arrangements to protect us from overly concentrated risk exposure could adversely affect our financial condition and results of operations. We monitor the financial condition of our reinsurers and attempt to place coverages only with carriers we view as substantial and financially sound. At December 31, 2007 and 2006, approximately 88.5% and 92.3%, respectively, of our reinsurance recoverables on paid and unpaid losses (not including prepaid reinsurance premiums) of $1.74 billion and $1.67 billion, respectively, were due from carriers which had an A.M. Best rating of "A-" or better. At December 31, 2007 and 2006, the largest reinsurance recoverables from any one carrier were less than 5.2% and 5.1%, respectively, of our total shareholders' equity. In connection with our acquisition of Arch Specialty in February 2002, the seller,

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Sentry, agreed to reinsure and guarantee all liabilities arising out of Arch Specialty's business prior to the closing of the acquisition. In addition to the guarantee provided by Sentry, substantially all of the recoverable from Sentry is still subject to the original reinsurance agreements inuring to Arch Specialty and, to the extent Sentry fails to comply with its payment obligations to us, we may obtain reimbursement from the third party reinsurers under such agreements.

Our reliance on brokers subjects us to their credit risk.

        In accordance with industry practice, we generally pay amounts owed on claims under our insurance and reinsurance contracts to brokers, and these brokers, in turn, pay these amounts to the clients that have purchased insurance or reinsurance from us. In some jurisdictions, if a broker fails to make such payment, we may remain liable to the insured or ceding insurer for the deficiency. Likewise, in certain jurisdictions, when the insured or ceding company pays the premiums for these contracts to brokers for payment to us, these premiums are considered to have been paid and the insured or ceding company will no longer be liable to us for those amounts, whether or not we have actually received the premiums from the broker. Consequently, we assume a degree of credit risk associated with our brokers. To date, we have not experienced any losses related to this credit risk.

We cannot predict the effect that the investigation currently being conducted by the New York Attorney General and others will have on the industry or our business, and the effects of emerging claims and coverage issues and certain proposed legislation are uncertain.

        The New York Attorney General and others are investigating allegations relating to contingent commission payments, bid-rigging and other practices in the insurance industry. We cannot predict the effect that these investigations, and any changes in insurance practice, including future legislation or regulations that may become applicable to us, will have on the insurance industry, the regulatory framework or our business.

        The effects of emerging claims and coverage issues are uncertain. The insurance industry is also affected by political, judicial and legal developments which have in the past resulted in new or expanded theories of liability. These or other changes could impose new financial obligations on us by extending coverage beyond our underwriting intent or otherwise require us to make unplanned modifications to the products and services that we provide, or cause the delay or cancellation of products and services that we provide. In some instances, these changes may not become apparent until some time after we have issued insurance or reinsurance contracts that are affected by the changes. As a result, the full extent of liability under our insurance or reinsurance contracts may not be known for many years after a contract is issued. The effects of unforeseen developments or substantial government intervention could adversely impact our ability to achieve our goals.

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Risks Relating to Our Company

Our success will depend on our ability to maintain and enhance effective operating procedures and internal controls.

        We continue to enhance our operating procedures and internal controls (including the timely and successful implementation of our information technology initiatives, which include the implementation of improved computerized systems and programs to replace and support manual systems, and including controls over financial reporting) to effectively support our business and our regulatory and reporting requirements. Our management does not expect that our disclosure controls or our internal controls will prevent all errors and all fraud. A control system, no matter how well conceived and operated, can provide only reasonable, not absolute, assurance that the objectives of the control system are met. Further, the design of a control system must reflect the fact that there are resource constraints, and the benefits of controls must be considered relative to their costs. As a result of the inherent limitations in all control systems, no evaluation of controls can provide absolute assurance that all control issues and instances of fraud, if any, within the company have been detected. These inherent limitations include the realities that judgments in decision-making can be faulty, and that breakdowns can occur because of simple error or mistake. Additionally, controls can be circumvented by the individual acts of some persons or by collusion of two or more people. The design of any system of controls also is based in part upon certain assumptions about the likelihood of future events, and there can be no assurance that any design will succeed in achieving its stated goals under all potential future conditions; over time, controls may become inadequate because of changes in conditions, or the degree of compliance with the policies or procedures may deteriorate. As a result of the inherent limitations in a cost-effective control system, misstatement due to error or fraud may occur and not be detected. Accordingly, our disclosure controls and procedures are designed to provide reasonable, not absolute, assurance that the disclosure controls and procedures are met.

A downgrade in our ratings or our inability to obtain a rating for our operating insurance and reinsurance subsidiaries may adversely affect our relationships with clients and brokers and negatively impact sales of our products.

        Our operating insurance and reinsurance subsidiaries are rated by ratings agencies. Brokers negotiate contracts of reinsurance between a primary insurer and reinsurer, on behalf of the primary insurer. Third-party rating agencies, such as A.M. Best Company, assess and rate the financial strength of insurers and reinsurers based upon criteria established by the rating agencies, which criteria are subject to change. Ratings have become an increasingly important factor in establishing the competitive position of insurance and reinsurance companies. Insurers and intermediaries use these ratings as one measure by which to assess the financial strength and quality of insurers and reinsurers. These ratings are often an important factor in the decision by an insured or intermediary of whether to place business with a particular insurance or reinsurance provider. Our financial strength ratings are subject to periodic review as rating agencies evaluate us to confirm that we continue to meet their criteria for ratings assigned to us by them. Such ratings may be revised downward or revoked at the sole discretion of such ratings agencies in response to a variety of factors, including a minimum capital adequacy ratio, management, earnings, capitalization and risk profile. We can offer no assurances that our ratings will remain at their current levels. A ratings downgrade or the potential for such a downgrade, or failure to obtain a necessary rating, could adversely affect both our relationships with agents, brokers, wholesalers and other distributors of our existing products and services and new sales of our products and services. Any ratings downgrade or failure to obtain a necessary rating could adversely affect our ability to compete in our markets, could cause our premiums and earnings to decrease and have a material adverse impact on our financial condition and results of operations. In addition, a downgrade in ratings of certain of our operating subsidiaries would in certain cases constitute an event of default under our credit facilities. See "Management's Discussion and Analysis of Financial Condition and Results of

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Operations—Contractual Obligations and Commercial Commitments—Letter of Credit and Revolving Credit Facilities" for a discussion of our credit facilities.

The loss of our key employees or our inability to retain them could negatively impact our business.

        Our success has been, and will continue to be, dependent on our ability to retain the services of our existing key executive officers and to attract and retain additional qualified personnel in the future. The pool of talent from which we actively recruit is limited. Although, to date, we have not experienced difficulties in attracting and retaining key personnel, the inability to attract and retain qualified personnel when available and the loss of services of key personnel could have a material adverse effect on our financial condition and results of operations. In addition, our underwriting staff is critical to our success in the production of business. While we do not consider any of our key executive officers or underwriters to be irreplaceable, the loss of the services of our key executive officers or underwriters or the inability to hire and retain other highly qualified personnel in the future could delay or prevent us from fully implementing our business strategy which could affect our financial performance. We are not aware of any intentions of any of our key personnel that would cause them no longer to provide their professional services to us in the near future.

The preparation of our financial statements requires us to make many estimates and judgments, which are even more difficult than those made in a mature company since limited historical information has been reported to us through December 31, 2007.

        The preparation of consolidated financial statements requires us to make many estimates and judgments that affect the reported amounts of assets, liabilities (including reserves), revenues and expenses, and related disclosures of contingent liabilities. On an ongoing basis, we evaluate our estimates, including those related to revenue recognition, insurance and other reserves, reinsurance recoverables, investment valuations, intangible assets, bad debts, income taxes, contingencies and litigation. We base our estimates on historical experience, where possible, and on various other assumptions that we believe to be reasonable under the circumstances, which form the basis for our judgments about the carrying values of assets and liabilities that are not readily apparent from other sources. Estimates and judgments for a relatively new insurance and reinsurance company, like our company, are even more difficult to make than those made in a mature company since limited historical information has been reported to us through December 31, 2007. Instead, our current loss reserves are primarily based on estimates involving actuarial and statistical projections of our expectations of the ultimate settlement and administration costs of claims incurred but not yet reported. We utilize actuarial models as well as historical insurance industry loss development patterns to establish loss reserves. Accordingly, actual claims and claim expenses paid may deviate, perhaps substantially, from the reserve estimates reflected in our financial statements.

The Warburg Pincus funds own approximately 16.3% of our voting shares, and they have the right to have directors on our board; their interests may materially differ from the interests of the holders of our other securities.

        The Warburg Pincus funds own approximately 16.3% of our outstanding voting shares as of December 31, 2007. These shareholders are not subject to the voting limitation contained in our bye-laws. We have agreed (until 2011) not to declare any dividend or make any other distribution on our common shares and not to repurchase any common shares until we have repurchased from the Warburg Pincus funds, pro rata, on the basis of the amount of their investment in us at the time of such repurchase, common shares (which were issued pursuant to the conversion of all of the outstanding preference shares in the 2005 fourth quarter) having an aggregate value of $250 million, at a per share price acceptable to them. No such shares have yet been repurchased.

        In addition, the Warburg Pincus funds are entitled (until 2011) to nominate a prescribed number of directors based on the respective retained percentages of their equity securities purchased in

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November 2001. Currently, our board consists of nine members, which includes three directors nominated by the Warburg Pincus funds. As long as the Warburg Pincus funds retain at least 45% of their original investment they will be entitled to nominate four directors.

        By reason of their ownership and the shareholders agreement, the Warburg Pincus funds are able to strongly influence or effectively control certain actions to be taken by us or our shareholders. The interests of these shareholders may differ materially from the interests of the holders of our other securities, and these shareholders could take actions or make decisions that are not in the interests of the holders of our other securities generally.

The price of our common shares may be volatile.

        There has been significant volatility in the market for equity securities. During 2007 and 2006, the price of our common shares fluctuated from a low of $63.25 to a high of $77.30 and from a low of $52.00 to a high of $70.59, respectively. On February 15, 2008, our common shares closed at a price of $70.82. The price of our common shares may not remain at or exceed current levels. The following factors may have an adverse impact on the market price of our common stock:

        Stock markets in the United States often experience price and volume fluctuations. Market fluctuations, as well as general political and economic conditions such as recession or interest rate or currency rate fluctuations, could adversely affect the market price of our stock.

Our business is dependent upon insurance and reinsurance brokers, and the loss of important broker relationships could materially adversely affect our ability to market our products and services.

        We market our insurance and reinsurance products primarily through brokers. We derive a significant portion of our business from a limited number of brokers. During 2007, approximately 19.6% and 16.4% of our gross premiums written were generated from or placed by Marsh & McLennan Companies and its subsidiaries and AON Corporation and its subsidiaries, respectively. No other broker and no one insured or reinsured accounted for more than 10% of gross premiums written for 2007. Some of our competitors have had longer term relationships with the brokers we use than we have, and the brokers may promote products offered by companies that may offer a larger variety of products than we do. Loss of all or a substantial portion of the business provided by these brokers could have a material adverse effect on us.

We could be materially adversely affected to the extent that managing general agents, general agents and other producers in our program business exceed their underwriting authorities or otherwise breach obligations owed to us.

        In program business conducted by our insurance group, following our underwriting, financial, claims and information technology due diligence reviews, we authorize managing general agents,

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general agents and other producers to write business on our behalf within underwriting authorities prescribed by us. Once a program incepts, we must rely on the underwriting controls of these agents to write business within the underwriting authorities provided by us. Although we monitor our programs on an ongoing basis, our monitoring efforts may not be adequate or our agents may exceed their underwriting authorities or otherwise breach obligations owed to us. We have experienced breaches by certain of our agents, all of which have been resolved favorably for us. To the extent that our agents exceed their authorities or otherwise breach obligations owed to us in the future, our financial condition and results of operations could be materially adversely affected.

Our investment performance may affect our financial results and ability to conduct business.

        Our operating results depend in part on the performance of our investment portfolio. A significant portion of our cash and invested assets consists of fixed maturities (85% as of December 31, 2007). Although our current investment guidelines and approach stress preservation of capital, market liquidity and diversification of risk, our investments are subject to market-wide risks and fluctuations. In addition, although we did not experience any significant defaults by issuers during 2007, we are subject to risks inherent in particular securities or types of securities, as well as sector concentrations. We may not be able to realize our investment objectives, which could reduce our net income significantly. In the event that we are unsuccessful in correlating our investment portfolio with our expected insurance and reinsurance liabilities, we may be forced to liquidate our investments at times and prices that are not optimal, which could have a material adverse effect on our financial results and ability to conduct our business.

We may be adversely affected by changes in economic conditions, including interest rate changes.

        Our operating results are affected, in part, by the performance of our investment portfolio. Our investment portfolio contains fixed and floating rate securities and instruments, such as bonds, which may be adversely affected by changes in interest rates. Changes in interest rates could also have an adverse effect on our investment income and results of operations. For example, if interest rates increase, the value of our investment portfolio may decline. Although lower interest rates may increase the value of our portfolio, our investment income might suffer from the lower rates at which new cash could be deployed.

        In addition, our investment portfolio includes residential mortgage-backed securities ("RMBS"). As of December 31, 2007, RMBS constituted approximately 12.8% of our cash and invested assets. As with other fixed income investments, the fair value of these securities fluctuates depending on market and other general economic conditions and the interest rate environment. Changes in interest rates can expose us to changes in the prepayment rate on these investments. In periods of declining interest rates, mortgage prepayments generally increase and RMBS are prepaid more quickly, requiring us to reinvest the proceeds at the then current market rates. Conversely, in periods of rising rates, mortgage prepayments generally fall, preventing us from taking full advantage of the higher level of rates.

        Interest rates are highly sensitive to many factors, including the fiscal and monetary policies of the U.S. and other major economies, inflation, economic and political conditions and other factors beyond our control. Although we attempt to take measures to manage the risks of investing in changing interest rate environments, we may not be able to mitigate interest rate sensitivity effectively. Despite our mitigation efforts, an increase in interest rates could have a material adverse effect on our book value.

        In recent months, delinquencies and losses with respect to residential mortgage loans generally have increased and may continue to increase, particularly in the subprime sector. In addition, in recent months residential property values in many states have declined or remained stable, after extended periods during which those values appreciated. A continued decline or an extended flattening in those values may result in additional increases in delinquencies and losses on residential mortgage loans

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generally, especially with respect to second homes and investment properties, and with respect to any residential mortgage loans where the aggregate loan amounts (including any subordinate loans) are close to or greater than the related property values. These developments may have a significant adverse effect on the prices of loans and securities, including those in our investment portfolio. The situation continues to have wide ranging consequences, including downward pressure on economic growth and the potential for increased insurance and reinsurance exposures, which could have an adverse impact on our results of operations, financial condition, business and operations.

We may require additional capital in the future, which may not be available or only available on unfavorable terms.

        We monitor our capital adequacy on a regular basis. The capital requirements of our business depend on many factors, including our ability to write new business successfully and to establish premium rates and reserves at levels sufficient to cover losses. Our ability to underwrite is largely dependent upon the quality of our claims paying and financial strength ratings as evaluated by independent rating agencies. To the extent that our existing capital is insufficient to fund our future operating requirements and/or cover claim losses, we may need to raise additional funds through financings or limit our growth. Any equity or debt financing, if available at all, may be on terms that are unfavorable to us. In the case of equity financings, dilution to our shareholders could result, and, in any case, such securities may have rights, preferences and privileges that are senior to those of our outstanding securities. If we are not able to obtain adequate capital, our business, results of operations and financial condition could be adversely affected. See "Management's Discussion and Analysis of Financial Condition and Results of Operations—Liquidity and Capital Resources."

We sold our prior reinsurance operations in May 2000 and may have liability to the purchaser and continuing liability from those reinsurance operations if the purchaser should fail to make payments on the reinsurance liabilities it assumed.

        On May 5, 2000, we sold our prior reinsurance operations to Folksamerica. The Folksamerica transaction was structured as a transfer and assumption agreement (and not reinsurance), and, accordingly, the loss reserves (and any related reinsurance recoverables) relating to the transferred business are not included as assets or liabilities on our balance sheet. In addition, in connection with that asset sale, we made extensive representations and warranties about us and our reinsurance operations, some of which survived the closing of the asset sale. Breach of these representations and warranties could result in liability for us. In the event that Folksamerica refuses or is unable to make payment for reserved losses transferred to it by us in the May 2000 sale and the notice given to reinsureds is found not to be an effective release by such reinsureds, we would be liable for such claims. A.M. Best Company has assigned a "A-" (Excellent) financial strength rating to Folksamerica. Folksamerica reported policyholders' surplus of $1.22 billion at September 30, 2007.

We sold our non-standard automobile insurance operations and merchant banking operations in 2004 and may have liability to the purchasers.

        In 2004, we sold our non-standard automobile insurance operations and merchant banking operations to third party purchasers. In connection with such sales, we made representations and warranties about us and our transferred businesses, some of which survived the closing of such sales. Breach of these representations and warranties could result in liability to us.

Any future acquisitions, growth of our operations through the addition of new lines of insurance or reinsurance business through our existing subsidiaries or through the formation of new subsidiaries, expansion into new geographic regions and/or joint ventures or partnerships may expose us to operational risks.

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        We may in the future make strategic acquisitions either of other companies or selected blocks of business, expand our business lines or enter into joint ventures. Any future acquisitions may expose us to operational challenges and risks, including:

        Our failure to manage successfully these operational challenges and risks may impact our results of operations.

Some of the provisions of our bye-laws and our shareholders agreement may have the effect of hindering, delaying or preventing third party takeovers or changes in management initiated by shareholders. These provisions may also prevent our shareholders from receiving premium prices for their shares in an unsolicited takeover.

        Some provisions of our bye-laws could have the effect of discouraging unsolicited takeover bids from third parties or changes in management initiated by shareholders. These provisions may encourage companies interested in acquiring the Company to negotiate in advance with our board of directors, since the board has the authority to overrule the operation of several of the limitations.

        Among other things, our bye-laws provide:

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        Our bye-laws provide that certain provisions which may have anti-takeover effects may be repealed or altered only with prior board approval and upon the affirmative vote of holders of shares representing at least 65% of the total voting power of our shares entitled generally to vote at an election of directors.

        The bye-laws also contain a provision limiting the rights of any U.S. person (as defined in section 7701(a)(30) of the Internal Revenue Code of 1986, as amended (the "Code")) that owns shares of ACGL, directly, indirectly or constructively (within the meaning of section 958 of the Code), representing more than 9.9% of the voting power of all shares entitled to vote generally at an election of directors. The votes conferred by such shares of such U.S. person will be reduced by whatever amount is necessary so that after any such reduction the votes conferred by the shares of such person will constitute 9.9% of the total voting power of all shares entitled to vote generally at an election of directors. Notwithstanding this provision, the board may make such final adjustments to the aggregate number of votes conferred by the shares of any U.S. person that the board considers fair and reasonable in all circumstances to ensure that such votes represent 9.9% of the aggregate voting power of the votes conferred by all shares of ACGL entitled to vote generally at an election of directors. ACGL will assume that all shareholders (other than the Warburg Pincus funds) are U.S. persons unless we receive assurance satisfactory to us that they are not U.S. persons.

        Moreover, most states, including states in which our subsidiaries are domiciled, have laws and regulations that require regulatory approval of a change in control of an insurer or an insurer's holding company. Where such laws apply to us and our subsidiaries, there can be no effective change in our control unless the person seeking to acquire control has filed a statement with the regulators and has obtained prior approval for the proposed change from such regulators. The usual measure for a presumptive change in control pursuant to these laws is the acquisition of 10% or more of the voting power of the insurance company or its parent, although this presumption is rebuttable. Consequently, a person may not acquire 10% or more of our common shares without the prior approval of insurance regulators in the state in which our subsidiaries are domiciled.

        The bye-laws also provide that the affirmative vote of 80% of our outstanding shares (including a majority of the outstanding shares held by shareholders other than holders (and such holders' affiliates) of 10% or more ("10% holders") of the outstanding shares) shall be required (the "extraordinary vote") for the following corporate actions:

provided, however, the extraordinary vote will not apply to any transaction approved by the board, so long as a majority of those board members voting in favor of the transaction were duly elected and acting members of the board prior to the time the 10% holder became a 10% holder.

        The provisions described above may have the effect of making more difficult or discouraging unsolicited takeover bids from third parties. To the extent that these effects occur, shareholders could be deprived of opportunities to realize takeover premiums for their shares and the market price of their shares could be depressed. In addition, these provisions could also result in the entrenchment of incumbent management.

Our operating insurance and reinsurance subsidiaries are subject to regulation in various jurisdictions, and material changes in the regulation of their operations could adversely affect our results of operations.

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        Our insurance and reinsurance subsidiaries are subject to government regulation in each of the jurisdictions in which they are licensed or authorized to do business. Governmental agencies have broad administrative power to regulate many aspects of the insurance business, which may include trade and claim practices, accounting methods, premium rates, marketing practices, claims practices, advertising, policy forms, and capital adequacy. These agencies are concerned primarily with the protection of policyholders rather than shareholders. Moreover, insurance laws and regulations, among other things:

        The National Association of Insurance Commissioners ("NAIC") continuously examines existing laws and regulations in the United States. We cannot predict the effect that any NAIC recommendations or proposed or future legislation or rule making in the United States or elsewhere may have on our financial condition or operations.

        Our Bermuda insurance and reinsurance subsidiary, Arch Re Bermuda, conducts its business from its offices in Bermuda and is not licensed or admitted to do business in any jurisdiction except Bermuda. Arch Re Swiss Branch conducts only reinsurance activities and is therefore not required to be licensed by the Swiss insurance regulator authorities. We do not believe that Arch Re Bermuda is subject to the insurance laws of any state in the United States; however, recent scrutiny of the insurance and reinsurance industry in the U.S. and other countries could subject Arch Re Bermuda to additional regulation. Our U.S. reinsurance subsidiary, Arch Re U.S., and our U.S. insurance subsidiaries, Arch Insurance, Arch Specialty, Arch E&S and Western Diversified, write reinsurance and insurance in the U.S. These subsidiaries are subject to extensive regulation under state statutes which delegate regulatory, supervisory and administrative powers to state insurance commissioners. Such regulation generally is designed to protect policyholders rather than investors.

        Arch-Europe, our European subsidiary, conducts its business from its offices in London, Germany, as well as its other branches in Italy, Spain and, in Denmark, through Arch Re Denmark. It is subject to the insurance regulations of the U.K. and those Member States where it has established branches with respect to the conduct of its business in such Member State, but it remains subject only to the financial and operational supervision by the FSA. Arch-Europe has the freedom to provide insurance services anywhere in the EEA subject to compliance with certain rules governing such provision, including notification to the FSA. Arch-Europe is also approved as an excess and surplus lines insurer in 14 states in the U.S. In addition, the Canadian branch of Arch Insurance writes insurance in Canada and is subject to federal, as well as provincial and territorial, regulation in Canada.

        Our U.S., Bermuda and U.K. insurance and reinsurance subsidiaries and the Canadian branch of Arch Insurance are required to maintain minimum capital and surplus as mandated by their respective jurisdictions of incorporation and, in some cases, by the jurisdictions in which those subsidiaries write business. Arch-Europe is required to maintain minimum capital surplus as mandated by the NAIC and certain states where it is approved as an excess and surplus lines insurer. All of our subsidiaries are currently in compliance with these capital and surplus requirements.

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        We periodically review our corporate structure in the U.S. so that we can optimally deploy our capital. Changes in that structure require regulatory approval. Delays or failure in obtaining any of these approvals could limit the amount of insurance that we can write in the U.S.

        If ACGL or any of our subsidiaries were to become subject to the laws of a new jurisdiction in which such entity is not presently admitted, ACGL or such subsidiary may not be in compliance with the laws of the new jurisdiction. Any failure to comply with applicable laws could result in the imposition of significant restrictions on our ability to do business, and could also result in fines and other sanctions, any or all of which could adversely affect our financial condition and results of operations.

If our Bermuda operating subsidiary becomes subject to insurance statutes and regulations in jurisdictions other than Bermuda or if there is a change in Bermuda law or regulations or the application of Bermuda law or regulations, there could be a significant and negative impact on our business.

        Arch Re Bermuda, our Bermuda insurance and reinsurance subsidiary, is a registered Bermuda Class 4 insurer. As such, it is subject to regulation and supervision in Bermuda. Bermuda insurance statutes and the regulations and policies of the BMA require Arch Re Bermuda to, among other things:

        These statutes and regulations may restrict our ability to write insurance and reinsurance policies, distribute funds and pursue our investment strategy.

        We do not presently intend for Arch Re Bermuda to be admitted to do business in the U.S., U.K. or any jurisdiction other than Bermuda. However, we cannot assure you that insurance regulators in the U.S., U.K. or elsewhere will not review the activities or Arch Re Bermuda or its subsidiaries or agents and claim that Arch Re Bermuda is subject to such jurisdiction's licensing requirements.

        Generally, Bermuda insurance statutes and regulations applicable to Arch Re Bermuda are less restrictive than those that would be applicable if they were governed by the laws of any states in the U.S. If in the future we become subject to any insurance laws of the U.S. or any state thereof or of any other jurisdiction, we cannot assure you that we would be in compliance with such laws or that complying with such laws would not have a significant and negative effect on our business.

        The process of obtaining licenses is very time consuming and costly and Arch Re Bermuda may not be able to become licensed in jurisdictions other than Bermuda should we choose to do so. The modification of the conduct of our business that would result if we were required or chose to become licensed in certain jurisdictions could significantly and negatively affect our financial condition and results of operations. In addition, our inability to comply with insurance statutes and regulations could significantly and adversely affect our financial condition and results of operations by limiting our ability to conduct business as well as subject us to penalties and fines.

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        Because Arch Re Bermuda is a Bermuda company, it is subject to changes in Bermuda law and regulation that may have an adverse impact on our operations, including through the imposition of tax liability or increased regulatory supervision. In addition, Arch Re Bermuda will be exposed to any changes in the political environment in Bermuda, including, without limitation, changes as a result of the independence issues currently being discussed in Bermuda. The Bermuda insurance and reinsurance regulatory framework recently has become subject to increased scrutiny in many jurisdictions, including the U.K. While we cannot predict the future impact on our operations of changes in the laws and regulation to which we are or may become subject, any such changes could have a material adverse effect on our business, financial condition and results of operations.

        As part of the BMA's ongoing review of Bermuda's insurance supervisory framework, the BMA is introducing a new risk-based capital model ("Bermuda Solvency Capital Requirement" or "BSCR") as a tool to assist both in measuring risk and determining appropriate capitalization. It is expected that formal legislation will come into force in 2008 to apply these standards. In addition, the BMA intends to allow insurers to make application to the BMA to use their own internal capital models instead of the BSCR in cases where insurers can establish that their respective internal capital models better reflect their company characteristics. The BMA intends to consult further with insurers on the finer details of these proposals prior to formally implementing them.

ACGL is a holding company and is dependent on dividends and other payments from its operating subsidiaries, which are subject to dividend restrictions, to make payments, including the payment of debt service obligations and operating expenses we may incur and any payments of dividends, redemption amounts or liquidation amounts with respect to our preferred shares and common shares.

        ACGL is a holding company whose assets primarily consist of the shares in our subsidiaries. Generally, ACGL depends on its available cash resources, liquid investments and dividends or other distributions from subsidiaries to make payments, including the payment of debt service obligations and operating expenses it may incur and any payments of dividends, redemption amounts or liquidation amounts with respect to our preferred shares and common shares. For 2007, 2006 and 2005, ACGL received dividends of $602.1 million, $22.1 million and $22.1 million, respectively, from Arch Re Bermuda. Such amounts were used to fund the share repurchase program, pay interest on ACGL's senior notes and for other corporate expenses.

        The ability of our regulated insurance and reinsurance subsidiaries to pay dividends or make distributions is dependent on their ability to meet applicable regulatory standards. Under Bermuda law, Arch Re Bermuda is required to maintain a minimum solvency margin (i.e., the amount by which the value of its general business assets must exceed its general business liabilities) equal to the greatest of (1) $100 million, (2) 50% of net premiums written (being gross premiums written by us less any premiums ceded by us, but we may not deduct more than 25% of gross premiums when computing net premiums written) and (3) 15% of loss and other insurance reserves. Arch Re Bermuda is prohibited from declaring or paying any dividends during any financial year if it is not in compliance with its minimum solvency margin or minimum liquidity ratio. In addition, Arch Re Bermuda is prohibited from declaring or paying in any financial year dividends of more than 25% of its total statutory capital and surplus (as shown on its previous financial year's statutory balance sheet) unless it files, at least seven days before payment of such dividends, with the BMA an affidavit stating that it will continue to meet the required margins. In addition, Arch Re Bermuda is prohibited, without prior approval of the BMA, from reducing by 15% or more its total statutory capital, as set out in its previous year's statutory financial statements. At December 31, 2007, as determined under Bermuda law, Arch Re Bermuda had statutory capital of $2.0 billion and statutory capital and surplus of $3.73 billion. Such amounts include interests in U.S. insurance and reinsurance subsidiaries. Accordingly, Arch Re Bermuda can pay approximately $933 million to ACGL during 2008 without providing an affidavit to the BMA, as discussed above. Our U.S. insurance and reinsurance subsidiaries can pay approximately

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$113.9 million in dividends or distributions to Arch-U.S., our U.S. holding company, which is owned by Arch Re Bermuda, during 2008 without prior regulatory approval. Such dividends or distributions may be subject to applicable withholding or other taxes. Arch-Europe can pay approximately £8.4 million, or $16.7 million, in dividends to ACGL during 2008 without prior notice and approval by the FSA.

        In addition, the ability of our insurance and reinsurance subsidiaries to pay dividends could be constrained by our dependence on financial strength ratings from independent rating agencies. Our ratings from these agencies depend to a large extent on the capitalization levels of our insurance and reinsurance subsidiaries.

        We believe that ACGL has sufficient cash resources and available dividend capacity to service its indebtedness and other current outstanding obligations.

If our Bermuda reinsurance subsidiary is unable to provide collateral to ceding companies, its ability to conduct business could be significantly and negatively affected.

        Arch Re Bermuda is a registered Bermuda insurance company and is not licensed or admitted as an insurer in any jurisdiction in the United States. Because insurance regulations in the United States do not permit insurance companies to take credit for reinsurance obtained from unlicensed or non-admitted insurers on their statutory financial statements unless security is posted, Arch Re Bermuda's contracts generally require it to post a letter of credit or provide other security. Although, to date, Arch Re Bermuda has not experienced any difficulties in providing collateral when required, if we are unable to post security in the form of letters of credit or trust funds when required, the operations of Arch Re Bermuda could be significantly and negatively affected.

We may become subject to taxes in Bermuda after March 28, 2016, which may have a material adverse effect on our results of operations.

        Under current Bermuda law, we are not subject to tax on income or capital gains. Furthermore, we have obtained from the Minister of Finance of Bermuda under the Exempted Undertakings Tax Protection Act, 1966, an assurance that, in the event that Bermuda enacts legislation imposing tax computed on profits, income, any capital asset, gain or appreciation, or any tax in the nature of estate duty or inheritance tax, then the imposition of the tax will not be applicable to us or our operations until March 28, 2016. We could be subject to taxes in Bermuda after that date. This assurance does not, however, prevent the imposition of taxes on any person ordinarily resident in Bermuda or any company in respect of its ownership of real property or leasehold interests in Bermuda.

Foreign currency exchange rate fluctuation may adversely affect our financial results.

        We write business on a worldwide basis, and our results of operations may be affected by fluctuations in the value of currencies other than the U.S. Dollar. The primary foreign currencies in which we operate are the Euro, the British Pound Sterling and the Canadian Dollar. Changes in foreign currency exchange rates can reduce our revenues and increase our liabilities and costs. We may therefore suffer losses solely as a result of exchange rate fluctuations. In order to mitigate the impact of exchange rate fluctuations, we have invested and expect to continue to invest in securities denominated in currencies other than the U.S. Dollar. Net foreign exchange losses, recorded in the statement of income, for 2007 were $44.0 million, compared to net foreign exchange losses for the year ended December 31, 2006 of $23.9 million. We hold investments in foreign currencies which are intended to mitigate our exposure to foreign currency fluctuations in our net insurance liabilities. However, changes in the value of such investments due to foreign currency rate movements are reflected as a direct increase to shareholders' equity and are not included in the statement of income. We have chosen not to hedge the currency risk on the capital contributed to Arch-Europe in May 2004, which is held in British Pounds Sterling. However, we intend to match Arch-Europe's projected liabilities in foreign currencies with investments in the same currencies. There can be no assurances

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that such arrangements will mitigate the negative impact of exchange rate fluctuations, and we may suffer losses solely as a result of exchange rate fluctuations. From inception through December 31, 2007, and based on currency spot rates at December 31, 2007, Arch Re Bermuda has recorded net premiums written of approximately $760 million from Euro-denominated contracts, $750 million from British Pound Sterling-denominated contracts and $260 million from Canadian Dollar-denominated contracts. In addition, Arch-Europe writes business in British Pound Sterling and Euros, and the Canadian branch of Arch Insurance writes business in Canadian Dollars.

Certain employees of our Bermuda operations are required to obtain work permits before engaging in a gainful occupation in Bermuda. Required work permits may not be granted or may not remain in effect.

        Under Bermuda law, only persons who are Bermudians, spouses of Bermudians, holders of a permanent resident's certificate or holders of a working resident's certificate ("exempted persons") may engage in gainful occupation in Bermuda without an appropriate governmental work permit. Our success may depend in part on the continued services of key employees in Bermuda. A work permit may be granted or renewed upon showing that, after proper public advertisement, no exempted person is available who meets the minimum standards reasonably required by the employer. The Bermuda government's policy places a six-year term limit on individuals with work permits, subject to certain exemptions for key employees. A work permit is issued with an expiry date (up to five years) and no assurances can be given that any work permit will be issued or, if issued, renewed upon the expiration of the relevant term. We consider our key officers in Bermuda to be Constantine Iordanou, our President and Chief Executive Officer (work permit expires November 12, 2009), Marc Grandisson, Chairman and Chief Executive Officer of Arch Worldwide Reinsurance Group (work permit expires May 12, 2010), John D. Vollaro, our Executive Vice President and Chief Financial Officer (work permit expires July 25, 2010) and Nicolas Papadopoulo, President and Chief Executive Officer of Arch Re Bermuda (work permit expires March 31, 2010). We also have other key positions in Bermuda held by persons who hold work permits subject to renewal. If work permits are not obtained or renewed for our principal employees, we could lose their services, which could materially affect our business.

The enforcement of civil liabilities against us may be difficult.

        We are a Bermuda company and in the future some of our officers and directors may be residents of various jurisdictions outside the United States. All or a substantial portion of our assets and the assets of those persons may be located outside the United States. As a result, it may be difficult for you to effect service of process within the United States upon those persons or to enforce in United States courts judgments obtained against those persons.

        We have appointed National Registered Agents, Inc., New York, New York, as our agent for service of process with respect to actions based on offers and sales of securities made in the United States. We have been advised by our Bermuda counsel, Conyers Dill & Pearman, that the United States and Bermuda do not currently have a treaty providing for reciprocal recognition and enforcement of judgments of U.S. courts in civil and commercial matters and that a final judgment for the payment of money rendered by a court in the United States based on civil liability, whether or not predicated solely upon the U.S. federal securities laws, would, therefore, not be automatically enforceable in Bermuda. We also have been advised by Conyers Dill & Pearman that a final and conclusive judgment obtained in a court in the United States under which a sum of money is payable as compensatory damages (i.e., not being a sum claimed by a revenue authority for taxes or other charges of a similar nature by a governmental authority, or in respect of a fine or penalty or multiple or punitive damages) may be the subject of an action on a debt in the Supreme Court of Bermuda under the common law doctrine of obligation. Such an action should be successful upon proof that the sum of money is due and payable, and without having to prove the facts supporting the underlying judgment, as long as:

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        A Bermuda court may impose civil liability on us or our directors or officers in a suit brought in the Supreme Court of Bermuda against us or such persons with respect to a violation of U.S. federal securities laws, provided that the facts surrounding such violation would constitute or give rise to a cause of action under Bermuda law.

Risk Relating to our Preferred Shares

General market conditions and unpredictable factors could adversely affect market prices for our outstanding preferred shares.

        There can be no assurance about the market prices for any series of our preferred shares. Several factors, many of which are beyond our control, will influence the market value of such series of preferred shares. Factors that might influence the market value of any series of our preferred shares include, but are not limited to:

Dividends on our preferred shares are non-cumulative.

        Dividends on our preferred shares are non-cumulative and payable only out of lawfully available funds of ACGL under Bermuda law. Consequently, if ACGL's board of directors (or a duly authorized committee of the board) does not authorize and declare a dividend for any dividend period with respect to any series of our preferred shares, holders of such preferred shares would not be entitled to receive any such dividend, and such unpaid dividend will not accrue and will never be payable. ACGL will have no obligation to pay dividends for a dividend period on or after the dividend payment date for such period if its board of directors (or a duly authorized committee of the board) has not declared such dividend before the related dividend payment date; if dividends on any series of our preferred shares are authorized and declared with respect to any subsequent dividend period, ACGL will be free to pay dividends on any other series of preferred shares and/or our common shares. In the past, we have not paid dividends on our common shares.

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Our preferred shares are equity and are subordinate to our existing and future indebtedness.

        Our preferred shares are equity interests and do not constitute indebtedness. As such, our preferred shares will rank junior to all of our indebtedness and other non-equity claims with respect to assets available to satisfy our claims, including in our liquidation. As of December 31, 2007, our total consolidated long-term debt was $300.0 million. We may incur additional debt in the future. Our existing and future indebtedness may restrict payments of dividends on our preferred shares. Additionally, unlike indebtedness, where principal and interest would customarily be payable on specified due dates, in the case of preferred shares like our preferred shares, (1) dividends are payable only if declared by the board of directors of ACGL (or a duly authorized committee of the board) and (2) as described above under "—Risks Relating to Our Company—ACGL is a holding company and is dependent on dividends and other payments from its operating subsidiaries, which are subject to dividend restrictions, to make payments, including the payment of debt service obligations and operating expenses we may incur and any payments of dividends, redemption amounts or liquidation amounts with respect to our preferred shares and common shares," we are subject to certain regulatory and other constraints affecting our ability to pay dividends and make other payments.

The voting rights of holders of our preferred shares are limited.

        Holders of our preferred shares have no voting rights with respect to matters that generally require the approval of voting shareholders. The limited voting rights of holders of our preferred shares include the right to vote as a class on certain fundamental matters that affect the preference or special rights of our preferred shares as set forth in the certificate of designations relating to each series of preferred shares. In addition, if dividends on any series of our preferred shares have not been declared or paid for the equivalent of six dividend payments, whether or not for consecutive dividend periods, holders of the outstanding preferred shares of any series will be entitled to vote for the election of two additional directors to our board of directors subject to the terms and to the limited extent as set forth in the certificate of designations relating to such series of preferred shares.

There is no limitation on our issuance of securities that rank equally with or senior to our preferred shares.

        We may issue additional securities that rank equally with or senior to our preferred shares without limitation. The issuance of securities ranking equally with or senior to our preferred shares may reduce the amount available for dividends and the amount recoverable by holders of such series in the event of a liquidation, dissolution or winding-up of ACGL.

A classification of any series of preferred shares by the NAIC may impact U.S. insurance companies that purchase such series.

        The NAIC, may from time to time, in its discretion, classify securities in insurers' portfolios as either debt, preferred equity or common equity instruments. The NAIC's written guidelines for classifying securities as debt, preferred equity or common equity include subjective factors that require the relevant NAIC examiner to exercise substantial judgment in making a classification. There is therefore a risk that any series of preferred shares may be classified by NAIC as common equity instead of preferred equity. The NAIC classification determines the amount of risk based capital ("RBC") charges incurred by insurance companies in connection with an investment in a security. Securities classified as common equity by the NAIC carry RBC charges that can be significantly higher than the RBC requirement for debt or preferred equity. Therefore, any classification of any series of preferred shares as common equity may adversely affect U.S. insurance companies that hold such series. In addition, a determination by the NAIC to classify such series as common equity may adversely impact the trading of such series in the secondary market.

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Risks Relating to Taxation

We and our non-U.S. subsidiaries may become subject to U.S. federal income taxation.

        ACGL and its non-U.S. subsidiaries intend to operate their business in a manner that will not cause them to be treated as engaged in a trade or business in the United States and, thus, will not be required to pay U.S. federal income taxes (other than U.S. excise taxes on insurance and reinsurance premium and withholding taxes on certain U.S. source investment income) on their income. However, because there is uncertainty as to the activities which constitute being engaged in a trade or business in the United States, there can be no assurances that the U.S. Internal Revenue Service will not contend successfully that ACGL or its non-U.S. subsidiaries are engaged in a trade or business in the United States. If ACGL or any of its non-U.S. subsidiaries were subject to U.S. income tax, our shareholders' equity and earnings could be adversely affected. Certain of our U.S. subsidiaries have been personal holding companies, but did not have "undistributed personal holding company income."

        Congress has been considering legislation intended to eliminate certain perceived tax advantages of Bermuda insurance companies and U.S. insurance companies having Bermuda affiliates, including perceived tax benefits resulting principally from reinsurance between or among U.S. insurance companies and their Bermuda affiliates. Some U.S. insurance companies have also been lobbying Congress recently to pass such legislation. In this regard, the American Jobs Creation Act of 2004 (the "Jobs Act") permits the United States Internal Revenue Service ("IRS") to re-allocate, re-characterize or adjust items of income, deduction or certain other items related to a reinsurance agreement between related parties to reflect the proper source, character and amount for each item (in contrast to prior law, which only covered source and character). The Jobs Act also eliminated the tax benefits available to a U.S. company that, after March 4, 2003, changed its legal domicile to a non-U.S. jurisdiction, a transaction commonly known as an inversion. We changed our legal domicile from the U.S. to Bermuda, but were not affected by the anti-inversion rule because our change in domicile occurred in November 2000. The American Infrastructure Investment and Improvement Act of 2007 as passed by the Senate Finance Committee would make the Jobs Act anti-inversion rule applicable retroactively to inversions that occurred after March 20, 2002. Although this modification would not affect ACGL, no assurance can be given that the final 2007 bill will not make the Jobs Act anti-inversion rule applicable retroactively to inversions that occurred on an earlier date, in which case ACGL could be adversely affected. Another legislative proposal has been introduced that would treat certain "tax haven CFCs" as U.S. corporations for federal income tax purposes. The term "tax haven CFC" would include a Bermuda corporation that is a controlled foreign corporation, but would exclude corporations that engage in the active conduct of a trade or business in Bermuda. It is not clear how this bill would apply to ACGL, which conducts its insurance and reinsurance businesses through its subsidiaries. Further, it is not clear whether this bill was intended to apply to a publicly traded company such as ACGL. There is no assurance that this legislative proposal, if enacted, would not apply to ACGL or any of its non-U.S. subsidiaries. In addition, Congress has recently conducted hearings relating to the tax treatment of reinsurance between affiliates and is reported to be considering legislation that would adversely affect reinsurance between U.S. and non-U.S. affiliates. One such proposal would increase the excise tax rate on reinsurance premiums paid to affiliated non-U.S. reinsurers; another proposal would limit deductions for premiums ceded to affiliated non-U.S. reinsurers above certain levels. Enactment of some version of such legislation as well as other changes in U.S. tax laws, regulations and interpretations thereof to address these issues could adversely affect us.

U.S. persons who hold our common shares or preferred shares may be subject to U.S. income taxation at ordinary income rates on our undistributed earnings and profits.

        We believe that we and our non-U.S. subsidiaries currently might be controlled foreign corporations ("CFCs"), although our bye-laws are designed to preclude a U.S. person (other than a U.S. person attributed shares owned by funds associated with the Warburg Pincus funds and

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Hellman & Friedman funds) from adverse tax consequences as a result of our CFC status. We do not believe that we are a passive foreign investment company. Since these determinations and beliefs are based upon legal and factual conclusions, no assurances can be given that the U.S. Internal Revenue Service or a court would concur with our conclusions. If they were not to so concur, U.S. persons who hold our common shares or preferred shares may suffer adverse tax consequences.

Reduced tax rate for qualified dividend income received by individuals and other non-corporate holders may not be available in the future.

        Dividends received by individuals and other non-corporate United States persons on our common shares or preferred shares in taxable years beginning on or before December 31, 2010 may constitute qualified dividend income that is subject to U.S. federal income tax at the rate applicable for long-term capital gains, rather than the higher rates applicable to ordinary income, provided that certain holding period requirements and other conditions are met. For taxable years beginning after December 31, 2010, qualified dividend income will no longer be taxed at the rate applicable for long-term capital gains unless legislation is enacted providing otherwise. In addition, there is proposed legislation before both Houses of Congress that would exclude shareholders of certain foreign corporations from this advantageous tax treatment. If this legislation becomes law, non-corporate U.S. shareholders would no longer qualify for the capital gains tax rate on the dividends paid by us.

Our non-U.S. companies may be subject to U.K. tax that may have a material adverse effect on our results of operations.

        We intend to operate in such a manner so that none of our companies, other than Arch-Europe and Arch-U.K., should be resident in the U.K. for tax purposes or have a permanent establishment in the U.K. Accordingly, we do not expect that any companies other than Arch-Europe and Arch-U.K. should be subject to U.K. taxation. However, since applicable law and regulations do not conclusively define the activities that constitute conducting business in the U.K. through a permanent establishment, the U.K. Inland Revenue might contend successfully that one or more of our companies, in addition to Arch-Europe and Arch-U.K., is conducting business in the U.K. through a permanent establishment in the U.K. and, therefore, subject to U.K. tax, which could have a material adverse effect on us.

ITEM 1B.    UNRESOLVED STAFF COMMENTS

        None.

ITEM 2.    PROPERTIES

        Our reinsurance group leases a total of approximately 9,100 square feet in Hamilton, Bermuda under a lease expiring in 2012, and approximately 19,200 square feet in Morristown, New Jersey under a lease expiring in 2011. Our property facultative reinsurance group leases approximately 14,490 square feet for its offices throughout the U.S. and in Toronto.

        Our insurance group leases approximately 8,750 square feet in Hamilton, Bermuda for our Bermuda insurance operations. The principal U.S. office of our insurance group is located at One Liberty Plaza, New York, New York where we lease approximately 161,880 square feet. Such lease expires in 2014, with the exception of a portion of that lease for approximately 28,390 square feet that expires in 2010. Our insurance group also leases a total of approximately 211,400 square feet for its other primary U.S. offices and its office in Canada.

        Arch-Europe leases approximately 18,900 square feet in London and 1,550 square feet in Germany. Arch Re Denmark, a branch of Arch-Europe, leases less than 1,000 square feet in Denmark. ACGL leases approximately 1,500 square feet in Bermuda. In addition, Arch Capital Services Inc., a subsidiary of ACGL which provides certain financial, legal and other administrative support services for ACGL and its subsidiaries, leases approximately 16,730 square feet in White Plains, New York.

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        For 2007, 2006 and 2005, our rental expense, net of income from subleases, was approximately $14.8 million, $12.9 million and $11.1 million, respectively. Our future minimum rental charges for the remaining terms of our existing leases, exclusive of escalation clauses and maintenance costs and net of rental income, will be approximately $91.2 million. We believe that the above described office space is adequate for our needs. However, as we continue to develop our business, we may open additional office locations during 2008.

ITEM 3.    LEGAL PROCEEDINGS

        We, in common with the insurance industry in general, are subject to litigation and arbitration in the normal course of our business. As of December 31, 2007, we were not a party to any material litigation or arbitration other than as a part of the ordinary course of business in relation to claims and reinsurance recoverable matters, none of which is expected by management to have a significant adverse effect on our results of operations and financial condition and liquidity.

ITEM 4.    SUBMISSION OF MATTERS TO A VOTE OF SECURITY HOLDERS

        None.

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PART II

ITEM 5.    MARKET FOR REGISTRANT'S COMMON EQUITY, RELATED STOCKHOLDER MATTERS AND ISSUER PURCHASES OF EQUITY SECURITIES

MARKET INFORMATION

        Our common shares are traded on the NASDAQ Stock Market under the symbol "ACGL." For the periods presented below, the high and low sales prices and closing prices for our common shares as reported on the NASDAQ Stock Market were as follows:

 
   Three Months Ended
 
   December 31, 2007
   September 30, 2007
   June 30, 2007
   March 31, 2007
High   $ 77.30   $ 75.28   $ 74.24   $ 68.58
Low   $ 66.38   $ 63.25   $ 68.04   $ 63.58
Close   $ 70.35   $ 74.41   $ 72.54   $ 67.46
 
 
   Three Months Ended
 
   December 31, 2006
   September 30, 2006
   June 30, 2006
   March 31, 2006
High   $ 70.59   $ 63.90   $ 62.60   $ 58.07
Low     62.71     56.46     55.42     52.00
Close     67.61     63.49     59.46     57.74

        On February 15, 2008 the high and low sales prices and the closing price for our common shares as reported on the NASDAQ Stock Market were $71.09, $69.06 and $70.82, respectively.


HOLDERS

        As of February 15, 2008, and based on information provided to us by our transfer agent and proxy solicitor, there were 149 holders of record of our common shares and approximately 34,500 beneficial holders of our common shares.


DIVIDENDS

        Any determination to pay dividends on ACGL's series A and series B non-cumulative preferred shares or common shares will be at the discretion of ACGL's board of directors (or a duly authorized committee of the board of directors) and will be dependent upon its results of operations, financial condition and other factors deemed relevant by ACGL's board of directors. As a holding company, ACGL will depend on future dividends and other permitted payments from its subsidiaries to pay dividends to its shareholders. ACGL's subsidiaries' ability to pay dividends, as well as its ability to pay dividends, is subject to regulatory, contractual, rating agency and other constraints. So long as any series A or series B non-cumulative preferred shares remain outstanding for any dividend period, unless the full dividends for the latest completed dividend period on all outstanding series A and series B non-cumulative preferred shares and parity shares have been declared and paid (or declared and a sum sufficient for the payment thereof has been set aside), (a) no dividend may be paid or declared on ACGL's common shares or any of its other securities ranking junior to the series A and series B non-cumulative preferred shares (other than a dividend payable solely in common shares or in such other junior securities) and (b) no common shares or other junior shares may be purchased, redeemed or otherwise acquired for consideration by ACGL, directly or indirectly (other than (i) as a result of a reclassification of junior shares for or into other junior shares, or the exchange or conversion of one junior share for or into another junior share, (ii) through the use of the proceeds of a substantially contemporaneous sale of junior shares and (iii) as permitted by the bye-laws of ACGL in effect on the date of issuance of the series A and series B non-cumulative preferred shares.

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        In addition, pursuant to a shareholders agreement, ACGL has agreed (until 2011) not to declare any dividend or make any other distribution on its common shares, and not to repurchase any common shares, until it has repurchased from the Warburg Pincus funds, pro rata, on the basis of the amount of their investment in us at the time of such repurchase, common shares (which were issued pursuant to the conversion of all outstanding preference shares in the 2005 fourth quarter) having an aggregate value of $250 million, at a per share price acceptable to them.


ISSUER PURCHASES OF EQUITY SECURITIES

        The following table summarizes our purchases of our common shares for the 2007 fourth quarter:

 
   Issuer Purchases of Equity Securities
    
Period
   Total Number
of Shares
Purchased(1)
   Average Price
Paid per Share
   Total Number of
Shares Purchased
as Part of
Publicly
Announced Plans
or Programs
   Approximate
Dollar Value of
Shares that May
Yet be Purchased
Under the Plan
or Programs(2)
10/1/2007–10/31/2007   —     —   196,300   $ 585,300
11/1/2007–11/30/2007   225   $ 71.75   734,649   $ 534,082
12/1/2007–12/31/2007   —     —   1,025,647   $ 462,934
   
 
 
     
Total   225   $ 71.75   1,956,596   $ 462,934
   
       
     
(1)
ACGL repurchases shares, from time to time, from employees in order to facilitate the payment of withholding taxes on restricted shares granted. We purchased these shares at their fair market value, as determined by reference to the closing price of our common shares on the day the restricted shares vested.

(2)
On February 28, 2007, ACGL's Board of Directors authorized ACGL to invest up to $1 billion in ACGL's common shares through a share repurchase program. Repurchases under the program may be effected from time to time in open market or privately negotiated transactions through February 2009. The timing and amount of the repurchase transactions under this program will depend on a variety of factors, including market conditions and corporate and regulatory considerations. In connection with the repurchase program, the Warburg Pincus funds and Hellman & Friedman funds waived their rights relating to share repurchases under the shareholders agreement for all repurchases of common shares by ACGL under the repurchase program in open market transactions and certain privately negotiated transactions. In May 2007, the Hellman & Friedman funds ceased to own shares of ACGL and their rights under the shareholders agreement with ACGL terminated.

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PERFORMANCE GRAPH

        The following graph compares the cumulative total shareholder return on our common shares for each of the last five years through December 31, 2007 to the cumulative total return, assuming reinvestment of dividends, of (1) Standard & Poor's ("S&P") 500 Composite Stock Index ("S&P 500 Index") and (2) the S&P 500 Property & Casualty Insurance Index. The share price performance presented below is not necessarily indicative of future results.


CUMULATIVE TOTAL SHAREHOLDER RETURN (1)(2)(3)

GRAPHIC

(1)
Stock price appreciation plus dividends.

(2)
The above graph assumes that the value of the investment was $100 on December 31, 2002. The closing price for our common shares on December 31, 2007 (i.e., the last trading day in 2007) was $70.35.

(3)
This graph is not "soliciting material," is not deemed filed with the SEC and is not to be incorporated by reference in any filing by us under the Securities Act of 1933, as amended or the Securities and Exchange Act of 1934, whether made before or after the date hereof and irrespective of any general incorporation language in any such filing.

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ITEM 6.    SELECTED FINANCIAL DATA

        The following table sets forth summary historical consolidated financial and operating data for the five-year period ended December 31, 2007 and should be read in conjunction with "Management's Discussion and Analysis of Financial Condition and Results of Operations" and our financial statements and the related notes.

 
   Years Ended December 31,
(U.S. dollars in thousands except share data)
  2007
   2006
   2005
   2004
   2003
Statement of Income Data:                              
Revenues:                              
  Net premiums written   $ 2,901,936   $ 3,017,418   $ 3,138,772   $ 2,980,032   $ 2,738,415
  Net premiums earned     2,944,650     3,081,665     2,977,716     2,915,882     2,212,599
  Net investment income     463,070     380,205     232,902     143,705     80,992
  Net realized gains (losses)     28,141     (19,437 )   (53,456 )   30,237     25,317
  Total revenues     3,452,445     3,452,678     3,167,529     3,104,050     2,343,737
Income before income taxes and extraordinary item     873,544     739,893     285,435     343,127     306,500
Income before extraordinary item     857,943     713,214     256,486     316,899     279,775
Extraordinary gain—excess of fair value of acquired net assets over cost (net of $0 tax)(1)     —     —     —     —     816
   
 
 
 
 
Net income     857,943     713,214     256,486     316,899     280,591
Preferred dividends     (25,844 )   (20,655 )   —     —     —
   
 
 
 
 
Net income available to common shareholders   $ 832,099   $ 692,559   $ 256,486   $ 316,899   $ 280,591
   
 
 
 
 

Weighted average common shares and common share equivalents outstanding:
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
  Basic(2)     70,995,672     73,212,432     35,342,650     31,560,737     26,264,055
  Diluted(2)     73,762,419     76,246,725     74,709,858     72,519,045     67,777,794
Net income (loss) per common share data:                              
Basic(2):                              
  Income before extraordinary item   $ 11.72   $ 9.46   $ 7.26   $ 10.04   $ 10.65
  Extraordinary gain(1)     —     —     —     —     0.03
   
 
 
 
 
  Net income available to common shareholders   $ 11.72   $ 9.46   $ 7.26   $ 10.04   $ 10.68
   
 
 
 
 
Diluted(2):                              
  Income before extraordinary item   $ 11.28   $ 9.08   $ 3.43   $ 4.37   $ 4.13
  Extraordinary gain(1)     —     —     —     —     0.01
   
 
 
 
 
  Net income available to common shareholders   $ 11.28   $ 9.08   $ 3.43   $ 4.37   $ 4.14
   
 
 
 
 
Cash dividends per share     —     —     —     —     —

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Balance Sheet Data:                              
Total investments and cash(3)   $ 10,129,663   $ 9,319,148   $ 7,119,450   $ 5,835,515   $ 3,717,147
Premiums receivable     729,628     749,961     672,902     520,781     477,032
Unpaid losses and loss adjustment expenses recoverable     1,609,619     1,552,157     1,389,768     617,607     369,080
Total assets     15,624,267     14,312,467     11,488,436     8,218,754     5,585,321

Reserves for losses and loss adjustment expenses:
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
  Before unpaid losses and loss adjustment expenses recoverable     7,092,452     6,463,041     5,452,826     3,492,759     1,911,596
  Net of unpaid losses and loss adjustment expenses recoverable     5,482,833     4,910,884     4,063,058     2,875,152     1,542,516
Unearned premiums:                              
  Before prepaid reinsurance premiums     1,765,881     1,791,922     1,699,691     1,518,162     1,378,654
  Net of prepaid reinsurance premiums     1,285,419     1,321,784     1,377,256     1,219,795     1,166,937
Senior notes     300,000     300,000     300,000     300,000     —
Revolving credit agreement borrowings     —     —     —     —     200,000
Total liabilities     11,588,456     10,721,848     9,007,909     5,976,848     3,874,592

Common shareholders' equity
 
 
3,710,811
 
 
3,265,619
 
 
2,480,527
 
 
2,241,906
 
 
1,710,729
Preferred shareholders' equity     325,000     325,000     —     —     —
Total shareholders' equity     4,035,811     3,590,619     2,480,527     2,241,906     1,710,729

Book value:
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
  Per common share(4)   $ 55.12   $ 43.97   $ 33.82   $ 41.76   $ 31.74
  Diluted(5)   $ 55.12   $ 43.97   $ 33.82   $ 31.03   $ 25.52
Shares outstanding:                              
  Basic     67,318,466     74,270,466     73,334,870     34,902,923     28,200,372
  Diluted(5)     67,318,466     74,270,466     73,334,870     72,251,073     67,045,037
(1)
On November 30, 2002, we acquired The Personal Service Insurance Co. ("PSIC"). In 2003, we recorded an extraordinary gain of $0.8 million representing an adjustment to the fair value of PSIC due to the recognition of deferred tax assets as part of the acquisition.

(2)
Net income per share is based on the basic and diluted weighted average number of common shares and common share equivalents outstanding.

(3)
In our securities lending transactions, we receive collateral in excess of the fair value of the fixed maturities and short-term investments pledged under securities lending agreements. For purposes of this table, we have excluded $1.5 billion, $891.4 million and $893.4 million, respectively, of collateral received which is reflected as "short-term investment of funds received under securities lending agreements, at fair value" and included $1.46 billion, $860.8 million and $863.9 million, respectively, of "fixed maturities and short-term investments pledged under securities lending agreements, at fair value" at December 31, 2007, 2006 and 2005.

(4)
Book value per common share at December 31, 2004 and 2003 was determined by dividing (i) the difference between total shareholders' equity and the aggregate liquidation preference of the series A convertible preference shares of $784.3 million and $815.7 million, respectively, by (ii) the number of common shares outstanding. All outstanding series A convertible preference shares were converted to common shares in 2005.

(5)
Book value per share excludes the effects of stock options and restricted stock units and, in periods prior to 2005, class B warrants.

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ITEM 7.    MANAGEMENT'S DISCUSSION AND ANALYSIS OF FINANCIAL CONDITION AND RESULTS OF OPERATIONS

        The following discussion and analysis contains forward-looking statements which involve inherent risks and uncertainties. All statements other than statements of historical fact are forward-looking statements. These statements are based on our current assessment of risks and uncertainties. Actual results may differ materially from those expressed or implied in these statements and, therefore, undue reliance should not be placed on them. Important factors that could cause actual events or results to differ materially from those indicated in such statements are discussed in this report, including the sections entitled "Cautionary Note Regarding Forward-Looking Statements," and "Risk Factors."

        This discussion and analysis should be read in conjunction with our audited consolidated financial statements and notes thereto presented under Item 8.

General

        Arch Capital Group Ltd. ("ACGL" and, together with its subsidiaries, "we" or "us") is a Bermuda public limited liability company with approximately $4.34 billion in capital at December 31, 2007 and, through operations in Bermuda, the United States, Europe and Canada, writes insurance and reinsurance on a worldwide basis. While we are positioned to provide a full range of property and casualty insurance and reinsurance lines, we focus on writing specialty lines of insurance and reinsurance. It is our belief that our underwriting platform, our experienced management team and our strong capital base that is unencumbered by significant pre-2002 risks have enabled us to establish a strong presence in the insurance and reinsurance markets.

        The worldwide insurance and reinsurance industry is highly competitive and has traditionally been subject to an underwriting cycle in which a hard market (high premium rates, restrictive underwriting standards, as well as terms and conditions, and underwriting gains) is eventually followed by a soft market (low premium rates, relaxed underwriting standards, as well as broader terms and conditions, and underwriting losses). Insurance market conditions may affect, among other things, the demand for our products, our ability to increase premium rates, the terms and conditions of the insurance policies we write, changes in the products offered by us or changes in our business strategy.

        The financial results of the insurance and reinsurance industry are influenced by factors such as the frequency and/or severity of claims and losses, including natural disasters or other catastrophic events, variations in interest rates and financial markets, changes in the legal, regulatory and judicial environments, inflationary pressures and general economic conditions. These factors influence, among other things, the demand for insurance or reinsurance, the supply of which is generally related to the total capital of competitors in the market.

        In general, market conditions improved during 2002 and 2003 in the insurance and reinsurance marketplace. This reflected improvement in pricing, terms and conditions following significant industry losses arising from the events of September 11th, as well as the recognition that intense competition in the late 1990s led to inadequate pricing and overly broad terms, conditions and coverages. Such industry developments resulted in poor financial results and erosion of the industry's capital base. Consequently, many established insurers and reinsurers reduced their participation in, or exited from, certain markets and, as a result, premium rates escalated in many lines of business. These developments provided relatively new insurers and reinsurers, like us, with an opportunity to provide needed underwriting capacity. Beginning in late 2003 and continuing through 2005, additional capacity emerged in many classes of business and, consequently, premium rate increases decelerated significantly and, in many classes of business, premium rates decreased. The weather-related catastrophic events that occurred in the second half of 2005 caused significant industry losses and led to a strengthening of rating agency capital requirements for catastrophe-exposed business. The 2005 events also resulted in

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substantial improvements in market conditions in property and certain marine lines of business and slowed declines in premium rates in other lines. During 2006 and 2007, excellent industry results led to a significant increase in capacity and, accordingly, competition intensified in 2007 and prices declined generally in all lines of business, including property. This trend is expected to continue in 2008.

        We increased our writings in property and certain marine lines of business in 2006 and 2007 in order to take advantage of improved market conditions and these lines represented a larger proportion of our overall book of business in 2006 and 2007 than in prior periods. We expect that our writings in these lines of business will continue to represent a significant proportion of our overall book of business in future periods and may represent a larger proportion of our overall book of business in future periods, which could increase the volatility in our results of operations. Although we saw price erosion in many of our lines in 2006 and 2007, current pricing remains at acceptable levels in many areas, even in lines for which rates have fallen. The most attractive area from a pricing point of view remains catastrophe-related property business. We believe that we are still able to write insurance and reinsurance business at what we believe to be acceptable rates. We maintained underwriting discipline during 2007 and, as a result, premiums written by our reinsurance operations were lower than in the 2006 period, while a significant portion of the increase in premiums written by our insurance operations was generated by expansion into the European market with moderate growth in the U.S. and Canadian markets. Such trend may continue as we respond to more challenging market conditions.

        In January 2007, we entered into a new line of business when we agreed to write excess workers' compensation and employers' liability insurance produced by a managing general agent, Wexford Underwriting Managers, Inc. ("Wexford"). For 2007, Wexford, which primarily serves not-for-profit clients, produced approximately $35 million of business for our insurance operations. During the 2007 fourth quarter, we completed the acquisition of the operations of Wexford, including the renewal rights of the subject business, through an asset purchase.

        In April 2007, we launched a new property facultative reinsurance operation headed by an experienced and well respected industry veteran. This unit is based in Farmington, Connecticut with branch offices across the United States and in Toronto, Canada. We view this business as a long-term opportunity that expands our specialty underwriting platform and will further diversify our book of business over time.

        In May 2007, Standard & Poor's Rating Services ("S&P") announced that it had upgraded the financial strength ratings of our principal operating subsidiaries from "A-" (Strong) to "A" (Strong). S&P also upgraded the counterparty credit and senior debt ratings on ACGL to "BBB+" from "BBB". The outlook on all of the ratings is stable.

        In January 2008, we announced that Arch Reinsurance Ltd. ("Arch Re Bermuda") finalized a joint venture agreement with Gulf Investment Corporation GSC ("GIC") to establish a new reinsurer to be based in the Dubai International Financial Centre. The joint venture will initially target the six member states of the Gulf Cooperation Council, which include Bahrain, Kuwait, Oman, Qatar, Saudi Arabia and the United Arab Emirates. Under the agreement, each of Arch Re Bermuda and GIC will own 50% of the joint venture. The joint venture will write a broad range of property and casualty reinsurance, including aviation, energy, commercial transportation, marine, engineered risks and property, on both a treaty and facultative basis. The initial total capital of the joint venture, which will be provided by Arch Re Bermuda and GIC equally, will consist of $200 million, plus an additional $200 million to be funded depending on the joint venture's business needs. The joint venture's underwriting activities are expected to commence during the first half of 2008, subject to approval by the Dubai Financial Services Authority.

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        We commenced operations in September 1995 following the completion of the initial public offering of our predecessor, Arch Capital Group (U.S.) Inc. ("Arch-U.S."). Arch-U.S. is a Delaware company formed in March 1995 under the original name of "Risk Capital Holdings, Inc." From that time until May 2000, we provided reinsurance and other forms of capital to insurance companies. On May 5, 2000, we sold our prior reinsurance book of business to Folksamerica Reinsurance Company ("Folksamerica") in an asset sale, but retained our surplus and our U.S.-licensed reinsurance platform. On November 8, 2000, following shareholder approval, we changed our legal domicile to Bermuda in order to benefit from Bermuda's favorable business, regulatory, tax and financing environment.

        During the period from May 2000 through the announcement of our underwriting initiative in October 2001, we built and acquired insurance businesses that were intended to enable us to generate both fee-based revenue (e.g., commissions and advisory and management fees) and risk-based revenue (i.e., insurance premium). As part of this strategy, we built an underwriting platform that was intended to enable us to maximize risk-based revenue during periods in the underwriting cycle when we believed it was more favorable to assume underwriting risk. In October 2001, we concluded that underwriting conditions favored dedicating our attention exclusively to building our insurance and reinsurance business.

        In October 2001, we launched an underwriting initiative to meet current and future demand in the global insurance and reinsurance markets that included the recruitment of new insurance and reinsurance management teams and an equity capital infusion of $763.2 million in the form of convertible preference shares. In April 2002, we completed an offering of common shares and received net proceeds of $179.2 million and, in September 2002, we received proceeds of $74.3 million from the exercise of class A warrants by our principal shareholders and certain other investors. In March 2004, we completed a public offering of common shares and received net proceeds of $179.3 million and, in May 2004, we completed a public offering of $300 million principal amount of 7.35% senior notes due May 1, 2034 and received net proceeds of $296.4 million, of which $200 million of the net proceeds was used to repay all amounts outstanding under our existing credit facility. In 2006, we issued $325.0 million of non-cumulative preferred shares in public offerings and received net proceeds of $314.4 million. On February 28, 2007, our Board of Directors authorized us to invest up to $1 billion in ACGL's common shares through a share repurchase program. Repurchases under the program may be effected from time to time in open market or privately negotiated transactions through February 2009. In 2007, we repurchased approximately 7.8 million common shares for an aggregate purchase price of $537.1 million.

        In the 2005 fourth quarter, all remaining outstanding convertible preference shares were converted to common shares. Since the preference shares were treated as common share equivalents in our reported financial results, the conversion had no impact on diluted earnings per share or diluted book value per share. However, the convertible preference shares were not included in basic calculations prior to their conversion to common shares and, due to the timing of the conversions, basic average shares outstanding and basic earnings per share for 2005 only reflect the impact of the preference share conversion for a small portion of the year. Management does not believe that the comparison of basic earnings per share is meaningful for the 2007, 2006 or 2005 periods presented and such amounts have not been presented or discussed herein.

        We derive our revenues primarily from the issuance of insurance policies and reinsurance contracts. Insurance and reinsurance premiums are driven by the volume and classes of business of the policies and contracts that we write which, in turn, are related to prevailing market conditions. The premium we charge for the risks assumed is also based on many assumptions. We price these risks well before our ultimate costs are known, which may extend many years into the future. In addition, our

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revenues include fee income and income we generate from our investment portfolio. Our investment portfolio is comprised primarily of fixed income investments that are classified as "available for sale." Under accounting principles generally accepted in the United States of America ("GAAP"), these investments are carried at fair value and unrealized gains and losses on the investments are not included in our statement of income. These unrealized gains and losses are included in accumulated other comprehensive income or loss as a separate component of shareholders' equity in our balance sheet.

        Our costs and expenses primarily consist of losses and loss adjustment expenses, acquisition expenses and other operating expenses. Losses and loss adjustment expenses include management's best estimate of the ultimate cost of claims incurred during a reporting period. Such costs consist of three components: paid losses, changes in estimated amounts for known losses ("case reserves"), and changes in reserves for incurred but not reported ("IBNR") losses. See "—Critical Accounting Policies, Estimates and Recent Accounting Pronouncements—Reserves for Losses and Loss Adjustment Expenses" for further discussion. Acquisition expenses, net of ceding commissions received from unaffiliated reinsurers, consist primarily of commissions, brokerage and taxes paid to obtain our business. A significant portion of such costs is paid based on a percentage of the premium written and will vary for each class or type of business that we underwrite. Other operating expenses consist primarily of certain company costs necessary to support our worldwide insurance and reinsurance operations. A large portion of such costs are compensation-related and include share-based compensation.

Critical Accounting Policies, Estimates and Recent Accounting Pronouncements

        The preparation of consolidated financial statements in accordance with GAAP requires us to make many estimates and judgments that affect the reported amounts of assets, liabilities (including reserves), revenues and expenses, and related disclosures of contingent liabilities. On an ongoing basis, we evaluate our estimates, including those related to revenue recognition, insurance and other reserves, reinsurance recoverables, allowance for doubtful accounts, investment valuations, intangible assets, bad debts, income taxes, contingencies and litigation. We base our estimates on historical experience, where possible, and on various other assumptions that we believe to be reasonable under the circumstances, which form the basis for our judgments about the carrying values of assets and liabilities that are not readily apparent from other sources. Estimates and judgments for a relatively new insurance and reinsurance company, like our company, are even more difficult to make than those made in a mature company since limited historical information has been reported to us through December 31, 2007. Actual results will differ from these estimates and such differences may be material. We believe that the following critical accounting policies require our more significant judgments and estimates used in the preparation of our consolidated financial statements.

        We are required by applicable insurance laws and regulations and GAAP to establish reserves for losses and loss adjustment expenses ("Loss Reserves") that arise from the business we underwrite. Loss Reserves for our insurance and reinsurance operations are balance sheet liabilities representing estimates of future amounts required to pay losses and loss adjustment expenses for insured or reinsured events which have occurred at or before the balance sheet date. Loss Reserves do not reflect contingency reserve allowances to account for future loss occurrences. Losses arising from future events will be estimated and recognized at the time the losses are incurred and could be substantial.

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        At December 31, 2007 and 2006, our Loss Reserves, net of unpaid losses and loss adjustment expenses recoverable, by type and by operating segment were as follows:

 
   December 31,
(U.S. dollars in thousands)
   2007
   2006
Insurance:            
  Case reserves.    $ 811,054   $ 619,981
  IBNR reserves     2,100,696     1,795,510
   
 
    Total net reserves   $ 2,911,750   $ 2,415,491
   
 
Reinsurance:            
  Case reserves.    $ 623,419   $ 605,113
  Additional case reserves     80,438     74,181
  IBNR reserves     1,867,226     1,816,099
   
 
    Total net reserves   $ 2,571,083   $ 2,495,393
   
 
Total:            
  Case reserves.    $ 1,434,473   $ 1,225,094
  Additional case reserves     80,438     74,181
  IBNR reserves     3,967,922     3,611,609
   
 
    Total net reserves   $ 5,482,833   $ 4,910,884
   
 

        Loss Reserves for our insurance operations are comprised of (1) case reserves for claims reported and (2) reserves for losses that have occurred but for which claims have not yet been reported, referred to as IBNR reserves. For our insurance operations, generally, claims personnel determine whether to establish a case reserve for the estimated amount of the ultimate settlement of individual claims. The estimate reflects the judgment of claims personnel based on general corporate reserving practices, the experience and knowledge of such personnel regarding the nature and value of the specific type of claim and, where appropriate, advice of counsel. Our insurance operations also contract with a number of outside third party administrators in the claims process who, in certain cases, have limited authority to establish case reserves. The work of such administrators is reviewed and monitored by our claims personnel. Loss Reserves are also established to provide for loss adjustment expenses ("LAE") and represent the estimated expense of settling claims, including legal and other fees and the general expenses of administering the claims adjustment process. Periodically, adjustments to the reported or case reserves may be made as additional information regarding the claims is reported or payments are made. IBNR reserves are established to provide for incurred claims which have not yet been reported to an insurer or reinsurer at the balance sheet date as well as to adjust for any projected variance in case reserving. IBNR reserves are derived by subtracting paid losses and LAE and case reserves from estimates of ultimate losses and loss adjustment expenses. Actuaries estimate ultimate losses and LAE using various generally accepted actuarial methods applied to known losses and other relevant information. Like case reserves, IBNR reserves are adjusted as additional information becomes known or payments are made. The process of estimating reserves involves a considerable degree of judgment by management and, as of any given date, is inherently uncertain.

        Ultimate losses and LAE are generally determined by extrapolation of claim emergence and settlement patterns observed in the past that can reasonably be expected to persist into the future. In forecasting ultimate losses and LAE with respect to any line of business, past experience with respect to that line of business is the primary resource, developed through both industry and company experience, but cannot be relied upon in isolation. Uncertainties in estimating ultimate losses and LAE

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are magnified by the time lag between when a claim actually occurs and when it is reported and settled. This time lag is sometimes referred to as the "claim-tail". The claim-tail for most property coverages is typically short (usually several months up to a few years). The claim-tail for certain professional liability, executive assurance and healthcare coverages, which are generally written on a claims-made basis, is typically longer than property coverages but shorter than casualty lines. The claim-tail for liability/casualty coverages, such as general liability, products liability, multiple peril coverage, and workers' compensation, may be especially long as claims are often reported and ultimately paid or settled years, even decades, after the related loss events occur. During the long claims reporting and settlement period, additional facts regarding coverages written in prior accident years, as well as about actual claims and trends, may become known and, as a result, our insurance operations may adjust their reserves. If management determines that an adjustment is appropriate, the adjustment is recorded in the accounting period in which such determination is made in accordance with GAAP. Accordingly, should Loss Reserves need to be increased or decreased in the future from amounts currently established, future results of operations would be negatively or positively impacted, respectively.

        In determining ultimate losses and LAE, the cost to indemnify claimants, provide needed legal defense and other services for insureds and administer the investigation and adjustment of claims are considered. These claim costs are influenced by many factors that change over time, such as expanded coverage definitions as a result of new court decisions, inflation in costs to repair or replace damaged property, inflation in the cost of medical services and legislated changes in statutory benefits, as well as by the particular, unique facts that pertain to each claim. As a result, the rate at which claims arose in the past and the costs to settle them may not always be representative of what will occur in the future. The factors influencing changes in claim costs are often difficult to isolate or quantify and developments in paid and incurred losses from historical trends are frequently subject to multiple and conflicting interpretations. Changes in coverage terms or claims handling practices may also cause future experience and/or development patterns to vary from the past. A key objective of actuaries in developing estimates of ultimate losses and LAE, and resulting IBNR reserves, is to identify aberrations and systemic changes occurring within historical experience and accurately adjust for them so that the future can be projected reliably. Because of the factors previously discussed, this process requires the substantial use of informed judgment and is inherently uncertain.

        At December 31, 2007 and 2006, Loss Reserves for our insurance operations by major line of business, net of unpaid losses and loss adjustment expenses recoverable, were as follows:

 
   December 31,
(U.S. dollars in thousands)
   2007
   2006
Casualty   $ 647,842   $ 564,959
Construction, surety and national accounts     518,541     385,149
Executive assurance     431,068     344,881
Professional liability     420,083     335,104
Programs     370,852     345,490
Property, marine and aviation.      345,177     304,004
Healthcare     153,018     125,913
Other     25,169     9,991
   
 
  Total net reserves   $ 2,911,750   $ 2,415,491
   
 

        The reserving method for our insurance operations to date has been, to a large extent, the expected loss method, which is commonly applied when limited loss experience exists. Any estimates and assumptions made as part of the reserving process could prove to be inaccurate due to several factors, including the fact that limited historical information has been reported to our insurance

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operations through December 31, 2007. See below for a discussion of the key assumptions in our insurance operations' reserving process.

        Although Loss Reserves are initially determined based on underwriting and pricing analysis, our insurance operations apply several generally accepted actuarial methods, as discussed below, on a quarterly basis to evaluate their Loss Reserves, in addition to the expected loss method, in particular for Loss Reserves from more mature accident years (the year in which a loss occurred). As noted below, beginning in 2005, our insurance operations began to give a relatively small amount of weight to their own experience following reviews of open claims on lines of business written on a claims-made basis for which they developed a reasonable level of credible data. Each quarter, as part of the reserving process, actuaries at our insurance operations reaffirm that the assumptions used in the reserving process continue to form a sound basis for the projection of liabilities. If actual loss activity differs substantially from expectations based on historical information, an adjustment to loss reserves may be supported. As time passes, estimated Loss Reserves for a given accident year will be based more on historical loss activity and patterns than on the initial assumptions based on pricing indications. Our insurance operations place more or less reliance on a particular actuarial method based on the facts and circumstances at the time the estimates of Loss Reserves are made. These methods generally fall into one of the following categories or are hybrids of one or more of the following categories:

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        In the initial reserving process for casualty business, primarily consisting of primary and excess exposures written on an occurrence basis, our insurance operations primarily rely on the expected loss method. The development of our insurance operations' casualty business may be unstable due to its long-tail nature and the occurrence of high severity events, as a portion of our insurance operations' casualty business is in high excess layers. As time passes, for a given accident year, additional weight is given to the paid and incurred B-F loss development methods and historical paid and incurred loss development methods in the reserving process. Our insurance operations make a number of key assumptions in reserving for casualty business, including that the pricing loss ratio is the best estimate of the ultimate loss ratio at the time the policy is entered into, that our insurance operations' loss development patterns, which are based on industry loss development patterns and adjusted to reflect differences in our insurance operations' mix of business, are reasonable and that our insurance operations' claims personnel and underwriters analyses of our exposure to major events are assumed to be our best estimate of our exposure to the known claims on those events. As noted earlier, due to the long claims reporting and settlement period for casualty business, additional facts regarding coverages written in prior accident years, as well as about actual claims and trends may become known and, as a result, our insurance operations may be required to adjust their casualty reserves. The expected loss ratios used in the initial reserving process for our insurance operations' casualty business for recent accident years have not varied significantly from earlier accident years due to the long-tail nature of the business written and the limited number of years of historical experience available for use in projecting loss experience using standard actuarial methods. As the credibility of historical experience for earlier accident years increases, the experience from these accident years will be given a greater weighting in the actuarial analysis to determine future accident year expected loss ratios, adjusted for changes in pricing, loss trends, terms and conditions and reinsurance structure.

        In the initial reserving process for property, marine and aviation business, which are primarily short-tail exposures, our insurance operations primarily rely on the expected loss method. For catastrophe-exposed business, our insurance operations' reserving process also includes the usage of catastrophe models for known events and a heavy reliance on analysis of individual catastrophic events and management judgment. The development of property losses can be unstable, especially for policies

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characterized by high severity, low frequency losses. As time passes, for a given accident year, additional weight is given to the paid and incurred B-F loss development methods and historical paid and incurred loss development methods in the reserving process. Our insurance operations make a number of key assumptions in their reserving process, including that historical paid and reported development patterns are stable, catastrophe models provide useful information about our exposure to catastrophic events that have occurred and our underwriters' judgment as to potential loss exposures can be relied on. The expected loss ratios used in the initial reserving process for our insurance operations' property business have varied over time due to changes in pricing, reinsurance structure, estimates of catastrophe losses, policy changes (such as attachment points, class and limits) and geographical distribution. As a result of the weather-related catastrophic events in the second half of 2005 (and to a lesser extent in 2004), there has been a substantial improvement in rates and market conditions in property lines. As losses in property lines are reported relatively quickly, expected loss ratios are selected for the current accident year based upon actual attritional loss ratios for earlier accident years, adjusted for rate changes, inflation, changes in reinsurance programs and expected attritional losses based on modeling. Due to the short-tail nature of property business, reported loss experience emerges quickly and ultimate losses are known in a reasonably short period of time.

        In addition to the assumptions and development characteristics noted above for casualty and property business, our insurance operations authorize managing general agents, general agents and other producers to write program business on their behalf within prescribed underwriting authorities. This adds additional complexity to the reserving process. To monitor adherence to the underwriting guidelines given to such parties, our insurance operations periodically perform claims due diligence reviews. In the initial reserving process for program business, consisting of property and liability exposures which are primarily written on an occurrence basis, our insurance operations primarily rely on the expected loss method. As time passes, for a given accident year, additional weight is given to the paid and incurred B-F loss development methods and historical paid and incurred loss development methods in the reserving process. The expected loss ratios used in the initial reserving process for our insurance operations' program business have varied over time depending on the type of exposures written (casualty or property) and changes in pricing, loss trends, reinsurance structure and changes in the underlying business.

        In the initial reserving process for executive assurance, professional liability and healthcare business, primarily consisting of medium-tail exposures written on a claims-made basis, our insurance operations primarily rely on the expected loss method. As time passes, for a given accident year, additional weight is given to the paid and incurred B-F loss development methods and historical paid and incurred loss development methods in the reserving process. Beginning in 2005, our insurance operations began to give a relatively small amount of weight to their own experience following reviews of open claims, in particular for lines of business written on a claims-made basis for which they developed a reasonable level of credible data. In general, the expected loss ratios for executive assurance, professional liability and healthcare business for recent accident years have not varied significantly from earlier accident years since this business is primarily written on a claims-made basis and is subject to high severity, low frequency losses. In addition, only a limited number of years of historical experience is available for use in projecting loss experience using standard actuarial methods. As the credibility of historical experience for earlier accident years increases, the experience from these accident years will be given a greater weighting in the actuarial analysis to determine future accident year expected loss ratios, adjusted for the occurrence or lack of large losses, changes in pricing, loss trends, terms and conditions and reinsurance structure.

        In the initial reserving process for construction and surety business, consisting of primary and excess casualty and contract surety coverages written on an occurrence and claims-made basis, our insurance operations primarily rely on the expected loss method. Such business is subject to the assumptions and development characteristics noted above for casualty business. As time passes, for a

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given accident year, additional weight is given to the paid and incurred B-F loss development methods and historical paid and incurred loss development methods in the reserving process. The expected loss ratios used in the initial reserving process for our insurance operations' construction and surety business for recent accident years have not varied significantly from earlier accident years due to the medium-tail nature of the business written and the limited number of years of historical experience available for use in actuarial methods. As the credibility of historical experience for earlier accident years increases, the experience from these accident years will be given a greater weighting in the actuarial analysis to determine future accident year expected loss ratios, adjusted for anticipated changes in the regulatory environment, pricing, loss trends, terms and conditions and reinsurance structure.

        For the years ended December 31, 2005 to 2007, on average, our insurance segment reported approximately $16.2 million of estimated net favorable development in prior year Loss Reserves, or approximately 0.9% of average beginning Loss Reserves. Of such amount, approximately $27.7 million came from long-tail lines, or 3.8% of average beginning Loss Reserves, and $14.6 million from medium-tail lines, or 1.8% of beginning Loss Reserves, offset partially by adverse development on $26.1 million from short-tail lines, or 9.2% of average beginning Loss Reserves. The average adverse development on short-tail lines primarily resulted from $30.8 million of adverse development recorded in 2006 on the 2005 catastrophic events and higher than expected claims development. For the year ended December 31, 2007, estimated net favorable development in prior year Loss Reserves was $12.7 million, or 0.5% of beginning Loss Reserves. Such amount consisted of approximately $26.9 million from long-tail lines, or 2.8% of beginning Loss Reserves, and $19.1 million from medium-tail lines, or 1.8% of beginning Loss Reserves, partially offset by adverse development of $33.3 million from short-tail lines primarily due to higher than expected claims development, or 8.5% of beginning Loss Reserves. For informational purposes, based on historical results, applying the 0.9% average estimated net favorable development in average beginning Loss Reserves for the years ended December 31, 2005 to 2007 to our insurance segment's net Loss Reserves of $2.91 billion at December 31, 2007 would result in an increase in income before income taxes of approximately $25.8 million, or $0.35 per diluted share, and applying the 0.5% of estimated net favorable development in beginning Loss Reserves for the year ended December 31, 2007 to such Loss Reserves would result in an increase in income before income taxes of approximately $15.3 million, or $0.21 per diluted share. The amounts noted above are informational only and should not be considered projections of future events. Future favorable or adverse development in our insurance segment's Loss Reserves is subject to numerous factors, and no assurances can be given that we will experience favorable development in our Loss Reserves or that our ultimate losses will not be significantly different than the amounts shown above, and such differences could directly and significantly impact earnings favorably or unfavorably in the period they are determined. Because of our insurance segment's limited operating history, the sensitivity analysis above is one way to gauge the impact of changes in the assumptions in our reserving process. For another estimate of potential variability in our insurance segment's Loss Reserves, see "—Simulation Results." Refer to "—Results of Operations" for a discussion on net favorable or adverse development of our insurance operations' prior year Loss Reserves.

        Loss Reserves for our reinsurance operations are comprised of (1) case reserves for claims reported, (2) additional case reserves ("ACRs") and (3) IBNR reserves. Our reinsurance operations receive reports of claims notices from ceding companies and record case reserves based upon the amount of reserves recommended by the ceding company. Case reserves on known events may be supplemented by ACRs, which are often estimated by our reinsurance operations' claims personnel ahead of official notification from the ceding company, or when our reinsurance operations' judgment regarding the size or severity of the known event differs from the ceding company. In certain instances,

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our reinsurance operations establish ACRs even when the ceding company does not report any liability on a known event. In addition, specific claim information reported by ceding companies or obtained through claim audits can alert our reinsurance operations to emerging trends such as changing legal interpretations of coverage and liability, claims from unexpected sources or classes of business, and significant changes in the frequency or severity of individual claims. Such information is often used in the process of estimating IBNR reserves.

        The estimation of Loss Reserves for our reinsurance operations is subject to the same risk factors as the estimation of Loss Reserves for our insurance operations. In addition, the inherent uncertainties of estimating such reserves are even greater for reinsurers, due primarily to: (1) the claim-tail for reinsurers is generally longer because claims are first reported to the ceding company and then to the reinsurer through one or more intermediaries, (2) the reliance on premium estimates, where reports have not been received from the ceding company, in the reserving process, (3) the potential for writing a number of reinsurance contracts with different ceding companies with the same exposure to a single loss event, (4) the diversity of loss development patterns among different types of reinsurance treaties or facultative contracts, (5) the necessary reliance on the ceding companies for information regarding reported claims and (6) the differing reserving practices among ceding companies.

        As with our insurance operations, the process of estimating Loss Reserves for our reinsurance operations involves a considerable degree of judgment by management and, as of any given date, is inherently uncertain. As discussed above, such uncertainty is greater for reinsurers compared to insurers. As a result, our reinsurance operations obtain information from numerous sources to assist in the process. Pricing actuaries from our reinsurance operations devote considerable effort to understanding and analyzing a ceding company's operations and loss history during the underwriting of the business, using a combination of ceding company and industry statistics. Such statistics normally include historical premium and loss data by class of business, individual claim information for larger claims, distributions of insurance limits provided, loss reporting and payment patterns, and rate change history. This analysis is used to project expected loss ratios for each treaty during the upcoming contract period.

        As mentioned above, there can be a considerable time lag from the time a claim is reported to a ceding company to the time it is reported to the reinsurer. The lag can be several years in some cases and may be attributed to a number of reasons, including the time it takes to investigate a claim, delays associated with the litigation process, the deterioration in a claimant's physical condition many years after an accident occurs, the case reserving approach of the ceding company, etc. In the reserving process, our reinsurance operations assume that such lags are predictable, on average, over time and therefore the lags are contemplated in the loss reporting patterns used in their actuarial methods. This means that our reinsurance operations must rely on estimates for a longer period of time than does an insurance company.

        Backlogs in the recording of assumed reinsurance can also complicate the accuracy of loss reserve estimation. As of December 31, 2007, there were no significant backlogs related to the processing of assumed reinsurance information at our reinsurance operations.

        Our reinsurance operations rely heavily on information reported by ceding companies, as discussed above. In order to determine the accuracy and completeness of such information, underwriters, actuaries, and claims personnel at our reinsurance operations often perform audits of ceding companies and regularly review information received from ceding companies for unusual or unexpected results. Material findings are usually discussed with the ceding companies. Our reinsurance operations sometimes encounter situations where they determine that a claim presentation from a ceding company is not in accordance with contract terms. In these situations, our reinsurance operations attempt to resolve the dispute with the ceding company. Most situations are resolved amicably and without the need for litigation or arbitration. However, in the infrequent situations where a resolution is not possible, our reinsurance operations will vigorously defend their position in such disputes.

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        At December 31, 2007 and 2006, Loss Reserves for our reinsurance operations by major line of business, net of unpaid losses and loss adjustment expenses recoverable, were as follows:

 
   December 31,
(U.S. dollars in thousands)
   2007
   2006
Casualty   $ 1,715,712   $ 1,545,363
Property excluding property catastrophe     295,728     306,990
Other specialty.      212,088     239,132
Marine and aviation     167,290     176,144
Property catastrophe     111,084     147,031
Other     69,181     80,733
   
 
  Total net reserves   $ 2,571,083   $ 2,495,393
   
 

        The reserving method for our reinsurance operations to date has been, to a large extent, the expected loss method, which is commonly applied when limited loss experience exists. Any estimates and assumptions made as part of the reserving process could prove to be inaccurate due to several factors, including the fact that limited historical information has been reported to our reinsurance operations through December 31, 2007. See below for a discussion of the key assumptions in our reinsurance operations' reserving process.

        Although Loss Reserves are initially determined based on underwriting and pricing analysis, our reinsurance operations apply several generally accepted actuarial methods, as discussed above, on a quarterly basis to evaluate their Loss Reserves in addition to the expected loss method, in particular for Loss Reserves from more mature underwriting years (the year in which business is underwritten). Each quarter, as part of the reserving process, actuaries at our reinsurance operations reaffirm that the assumptions used in the reserving process continue to form a sound basis for projection of liabilities. If actual loss activity differs substantially from expectations based on historical information, an adjustment to loss reserves may be supported. As time passes, for a given underwriting year, the reserving process to estimate Loss Reserves will be based more on actual loss activity and historical patterns than on initial assumptions based on pricing indications. Our reinsurance operations place more or less reliance on a particular actuarial method based on the facts and circumstances at the time the estimates of Loss Reserves are made.

        In the initial reserving process for medium-tail and long-tail lines, consisting of casualty, other specialty, marine and aviation and other exposures, our reinsurance operations primarily rely on the expected loss method. The development of medium-tail and long-tail business may be unstable, especially if there are high severity major events, with business written on an excess of loss basis typically having a longer tail than business written on a pro rata basis. As time passes, for a given underwriting year, additional weight is given to the paid and incurred B-F loss development methods and historical paid and incurred loss development methods in the reserving process. Our reinsurance operations make a number of key assumptions in reserving for medium-tail and long-tail lines, including that the pricing loss ratio is the best estimate of the ultimate loss ratio at the time the contract is entered into, historical paid and reported development patterns are stable and our reinsurance operations' claims personnel and underwriters analyses of our exposure to major events are assumed to be our best estimate of our exposure to the known claims on those events. The expected loss ratios used in our reinsurance operations' initial reserving process for medium-tail and long-tail contracts have varied over time due to changes in pricing, terms and conditions and reinsurance structure. As the credibility of historical experience for earlier underwriting years increases, the experience from these underwriting years will be used in the actuarial analysis to determine future underwriting year expected loss ratios, adjusted for changes in pricing, loss trends, terms and conditions and reinsurance structure.

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        The process of estimating Loss Reserves for our reinsurance operations involves a considerable degree of judgment by management and, as of any given date, is inherently uncertain. The inherent uncertainties of estimating such reserves are even greater for reinsurers than for insurers due to the longer claim-tail for reinsurers, the reliance on premium estimates in the reserving process, the diversity and instability of loss development patterns, the necessary reliance on the ceding companies for information regarding reported claims and the differing reserving practices among ceding companies. In addition, as a result of the start up nature of our reinsurance operations in 2002 and 2003, the assumptions used in the initial loss estimates were subject to greater uncertainty than for an established company, especially for casualty reinsurance exposures (which have a longer claim-tail and involve a higher degree of judgment by management than short-tail lines). In the reserving process in 2002 and 2003, our reinsurance operations recognized that there is a possibility that the assumptions made could prove to be inaccurate due to the factors discussed above related to the start up nature of their operations in both periods.

        In response to such factors, and their impact on the credibility of the initial loss estimates for casualty reinsurance exposures, a provision was included in establishing our reinsurance operations' net Loss Reserves in 2002 and 2003 on casualty losses occurring prior to each balance sheet date. As of December 31, 2003, the provision, included in IBNR, was $49.0 million (or 5.0% of our reinsurance operations' net Loss Reserves). Due to the additional data our reinsurance operations had gained on its existing book of business by the end of 2003, it was determined that it was no longer necessary to continue to include a provision in the reserving process beginning in 2004. Based on the recommendation of an independent actuarial firm, our reinsurance operations adopted a methodology to evaluate the existing provision by comparing actual claims experience to a schedule of expected claims experience prepared by the independent actuarial firm. If the actual claims experience is in line with the expected claims experience, a reduction of the provision is made based on the schedule established in the review. For 2007, 2006 and 2005, following reviews of actual and expected claims experience, our reinsurance operations reduced the provision by $10.6 million, $7.7 million and $12.1 million, respectively. At December 31, 2007, the remaining provision included in our reinsurance operations' Loss Reserves was $11.3 million (or 0.4% of our reinsurance operations' net Loss Reserves), compared to $21.9 million (or 0.9% of our reinsurance operations' net Loss Reserves) at December 31, 2006.

        In the initial reserving process for short-tail lines, consisting of property excluding property catastrophe and property catastrophe exposures, our reinsurance operations primarily rely on the expected loss method. For known catastrophic events, our reinsurance operations' reserving process also includes the usage of catastrophe models and a heavy reliance on analysis which includes ceding company inquiries and management judgment. The development of property losses may be unstable, especially where there is high catastrophic exposure, may be characterized by high severity, low frequency losses for excess and catastrophe-exposed business and may be highly correlated across contracts. As time passes, for a given underwriting year, additional weight is given to the paid and incurred B-F loss development methods and historical paid and incurred loss development methods in the reserving process. Our reinsurance operations make a number of key assumptions in reserving for short-tail lines, including that historical paid and reported development patterns are stable, catastrophe models provide useful information about our exposure to catastrophic events that have occurred and our underwriters' judgment and guidance received from ceding companies as to potential loss exposures may be relied on. The expected loss ratios used in the initial reserving process for our reinsurance operations' property exposures have varied over time due to changes in pricing, reinsurance structure, estimates of catastrophe losses, terms and conditions and geographical distribution. As losses in property lines are reported relatively quickly, expected loss ratios are selected for the current underwriting year incorporating the experience for earlier underwriting years, adjusted for rate changes, inflation, changes in reinsurance programs, expectations about present and future market conditions and expected attritional losses based on modeling. Due to the short-tail nature of property business,

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reported loss experience emerges quickly and ultimate losses are known in a reasonably short period of time.

        For the years ended December 31, 2005 to 2007, on average, our reinsurance segment reported approximately $110.8 million of estimated net favorable development in prior year Loss Reserves, or 5.2% of average beginning Loss Reserves. Of such amount, approximately $77.7 million came from short-tail lines, or 11.1% of average beginning Loss Reserves, and $33.1 million came from medium-tail and long-tail lines, or 2.3% of average beginning Loss Reserves. For the year ended December 31, 2007, estimated net favorable development in prior year Loss Reserves was $172.7 million, or 6.9% of beginning Loss Reserves. Of such amount, approximately $110.6 million came from short-tail lines, or 15.2% of beginning Loss Reserves, and $62.1 million came from medium-tail and long-tail lines, or 3.5% of beginning Loss Reserves. For informational purposes, based on our reinsurance segment's historical results, applying the 5.2% average estimated net favorable development in average beginning Loss Reserves for the years ended December 31, 2005 to 2007 to our reinsurance segment's net Loss Reserves of $2.57 billion at December 31, 2007 would result in an increase in income before income taxes of approximately $134.5 million, or $1.82 per diluted share, while using the 6.9% of estimated net favorable development in beginning Loss Reserves for the year ended December 31, 2007 to such Loss Reserves would result in an increase in income before income taxes of approximately $177.9 million, or $2.41 per diluted share. The amounts noted above are informational only and should not be considered projections of future events. Future favorable or adverse development in our reinsurance segment's Loss Reserves is subject to numerous factors, and no assurances can be given that we will experience favorable development in our Loss Reserves or that our ultimate losses will not be significantly different than the amounts shown above, and such differences could directly and significantly impact earnings favorably or unfavorably in the period they are determined. Because of our reinsurance segment's limited operating history, the sensitivity analysis above is one way to gauge the impact of changes in the assumptions in our reserving process. For another estimate of potential variability in our reinsurance segment's Loss Reserves, see "—Simulation Results." Refer to "—Results of Operations" for additional discussion on net favorable or adverse development of our reinsurance operations' prior year Loss Reserves.

        Generally, due to the insufficient amount of historical loss data for our insurance and reinsurance operations in many lines of business, we do not produce a range of estimates in calculating reserves. As described above, we primarily use the expected loss method to calculate our initial Loss Reserves, and such amounts represent management's best estimate of our ultimate liabilities. As the loss data has developed, other actuarial methods have been given more weight in our reserving process for certain lines of business. In order to illustrate the potential volatility in our reserves for losses and loss adjustment expenses, we used a statistical model to simulate a range of results based on various probabilities. Both the probabilities and related modeling are subject to inherent uncertainties. The simulation relies on a significant number of assumptions, such as the potential for multiple entities to react similarly to external events, and includes other statistical assumptions.

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        Our recorded estimate of reserves for losses and loss adjustment expenses, net of unpaid losses and loss adjustment expenses recoverable, by operating segment at December 31, 2007, along with the results of the simulation are as follows:

 
   December 31, 2007
(U.S. dollars in thousands)
   Insurance
   Reinsurance
   Total
Total net reserves   $ 2,911,750   $ 2,571,083   $ 5,482,833
   
 
 
Simulation results:                  
  90th percentile(1)   $ 3,486,739   $ 3,341,962   $ 6,590,695
  10th percentile(2)   $ 2,382,306   $ 1,903,577   $ 4,477,747
(1)
Simulation results indicate that a 90% probability exists that the net reserves for losses and loss adjustment expenses will not exceed the indicated amount.

(2)
Simulation results indicate that a 10% probability exists that the net reserves for losses and loss adjustment expenses will be at or below the indicated amount.

        The simulation results shown for each segment do not add to the total simulation results, as the individual segment simulation results do not reflect the diversification effects across our segments. For informational purposes, based on the total simulation results, a change in our Loss Reserves to the amount indicated at the 90th percentile would result in a decrease in income before income taxes of approximately $1.11 billion, or $15.01 per diluted share, while a change in our Loss Reserves to the amount indicated at the 10th percentile would result in an increase in income before income taxes of approximately $1.01 billion, or $13.63 per diluted share. The simulation results noted above are informational only, and no assurance can be given that our ultimate losses will not be significantly different than the simulation results shown above, and such differences could directly and significantly impact earnings favorably or unfavorably in the period they are determined.

        We do not have significant exposure to pre-2002 liabilities, such as asbestos-related illnesses and other long-tail liabilities and, to date, we have experienced a relatively low level of reported claims activity in many lines of business, particularly in longer-tailed lines such as primary and excess casualty and executive assurance, which have longer time periods during which claims are reported and paid. Our limited history does not provide meaningful trend information for such lines of business.

        In the normal course of business, our insurance operations cede a substantial portion of their premium through pro rata, excess of loss and facultative reinsurance agreements. Our reinsurance operations also obtain reinsurance whereby another reinsurer contractually agrees to indemnify it for all or a portion of the reinsurance risks underwritten by our reinsurance operations. Such arrangements, where one reinsurer provides reinsurance to another reinsurer, are usually referred to as "retrocessional reinsurance" arrangements. In addition, our reinsurance subsidiaries participate in "common account" retrocessional arrangements for certain pro rata treaties. Such arrangements reduce the effect of individual or aggregate losses to all companies participating on such treaties, including the reinsurers, such as our reinsurance operations, and the ceding company. Reinsurance recoverables are recorded as assets, predicated on the reinsurers' ability to meet their obligations under the reinsurance agreements. If the reinsurers are unable to satisfy their obligations under the agreements, our insurance or reinsurance operations would be liable for such defaulted amounts.

        The availability and cost of reinsurance and retrocessional protection is subject to market conditions, which are beyond our control. Although we believe that our insurance and reinsurance operations have been successful in obtaining reinsurance and retrocessional protection, it is not certain that they will be able to continue to obtain adequate protection at cost effective levels. As a result of

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such market conditions and other factors, our insurance and reinsurance operations may not be able to successfully mitigate risk through reinsurance and retrocessional arrangements and may lead to increased volatility in our results of operations in future periods. See "Risk Factors—Risks Relating to Our Industry—The failure of any of the loss limitation methods we employ could have a material adverse effect on our financial condition or results of operations."

        In addition to the use of individual per risk and inuring reinsurance contracts to limit exposure, our insurance operations had in force during 2005 a catastrophe reinsurance program which provides coverage for certain property catastrophe-related losses occurring during the contract period equal to a maximum of 95% of the first $200 million in excess of a $50 million retention per occurrence of such losses. Estimated losses related to Hurricane Katrina and Hurricane Wilma have exceeded the per occurrence retention. Based on current estimates, and net of payments to date, our insurance operations has recorded recoverables of approximately $43.6 million through such coverage for Hurricane Katrina and $2.6 million for Hurricane Wilma with approximately $65.8 million of remaining available coverage for Hurricane Katrina and $187.4 million of remaining available coverage for Hurricane Wilma should the actual amount of losses ultimately attributable to such events exceed current estimates. Amounts shown for Hurricane Katrina are net of reinstatement premiums.

        Estimates for our insurance operations related to Hurricanes Katrina, Rita and Wilma and other catastrophic events that occurred in the second half of 2005 are based on currently available information derived from modeling techniques, industry assessments of exposure, claims information obtained from its clients and brokers to date and a review of its in-force contracts. Actual losses from these events may vary materially from the insurance operations' estimates due to the inherent uncertainties in making such determinations resulting from several factors, including the potential inaccuracies and inadequacies in the data provided by clients and brokers, the modeling techniques and the application of such techniques, the contingent nature of business interruption exposures, the effects of any resultant demand surge on claims activity and attendant coverage issues. In addition, actual losses may increase if reinsurers dispute or fail to meet their obligations to our insurance operations or the reinsurance protections purchased by our insurance operations are exhausted or are otherwise unavailable.

        Our insurance operations had in effect during 2007 a reinsurance program which provided coverage equal to a maximum of 88% of the first $325 million in excess of a $75 million retention per occurrence for certain property catastrophe-related losses occurring during 2007, compared to a reinsurance program in effect during 2006 which provided coverage equal to a maximum of 92% of the first $325 million in excess of a $75 million retention per occurrence for certain property catastrophe-related losses occurring during 2006. In the 2008 first quarter, our insurance operations renewed its reinsurance program which provides coverage for certain property-catastrophe related losses occurring during 2008 equal to a maximum of 70% of the first $275 million in excess of a $75 million retention per occurrence.

        On December 29, 2005, Arch Re Bermuda entered into a quota share reinsurance treaty with Flatiron Re Ltd., a Bermuda reinsurance company, pursuant to which Flatiron Re Ltd. assumed a 45% quota share (the "Flatiron Treaty") of certain lines of property and marine business underwritten by Arch Re Bermuda for unaffiliated third parties for the 2006 and 2007 underwriting years (January 1, 2006 to December 31, 2007). Effective June 28, 2006, the parties amended the Flatiron Treaty to increase the percentage ceded to Flatiron Re Ltd. from 45% to 70% of all covered business bound by Arch Re Bermuda from (and including) June 28, 2006 until (and including) August 15, 2006, provided such business does not incept beyond September 30, 2006. The ceding percentage for all business bound outside of this period continued to be 45%.

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        Arch Re Bermuda pays to Flatiron Re Ltd. a reinsurance premium in the amount of the ceded percentage of the original gross written premium on the business reinsured with Flatiron Re Ltd. less a ceding commission, which includes a reimbursement of direct acquisition expenses as well as a commission to Arch Re Bermuda for generating the business. The Flatiron Treaty also provides for a profit commission to Arch Re Bermuda based on the underwriting results for the 2006 and 2007 underwriting years on a cumulative basis. Arch Re Bermuda records such profit commission based on underwriting experience recorded each quarter. As a result, the profit commission arrangement with Flatiron Re Ltd. may increase the volatility of our reported results of operations on both a quarterly and annual basis. On December 31, 2007, the Flatiron Treaty expired by its terms. At December 31, 2007, $144.9 million of premiums ceded to Flatiron Re Ltd. were unearned. The attendant premiums earned, losses incurred and acquisition expenses will primarily be reflected in the reinsurance segment's results in the first half of 2008.

        Our reinsurance operations previously purchased a catastrophe reinsurance program which provides up to $55 million of coverage in excess of certain deductibles for any one occurrence and $110 million in the aggregate annually, for certain catastrophe-related losses worldwide occurring during the period from May 2005 through April 2006. Based on current estimates, and net of payments to date, our reinsurance operations have recorded recoverables of approximately $46.0 million, net of reinstatement premiums, related to the 2005 catastrophic events. The recovery represents full usage of the available coverage under the reinsurance program, and the coverage was not renewed upon expiration. Estimates for our reinsurance operations related to Hurricanes Katrina, Rita and Wilma and other catastrophic events that occurred in the second half of 2005 are based on currently available information derived from modeling techniques, industry assessments of exposure, claims information obtained from its clients and brokers to date and a review of its in-force contracts. Actual losses from these events may vary materially from our reinsurance operations' estimates due to the inherent uncertainties in making such determinations resulting from several factors, including the potential inaccuracies and inadequacies in the data provided by clients and brokers, the modeling techniques and the application of such techniques, the contingent nature of business interruption exposures, the effects of any resultant demand surge on claims activity and attendant coverage issues. In addition, actual losses may increase if reinsurers dispute or fail to meet their obligations to our reinsurance operations or the reinsurance protections purchased by our reinsurance operations are otherwise unavailable. While our reinsurance operations may purchase industry loss warranty contracts and other reinsurance which is intended to limit their exposure, the non-renewal of the catastrophe reinsurance program and the Flatiron Treaty increases the risk retention of our reinsurance operations and, as a result, may increase the volatility in our results of operations in future periods.

        Insurance premiums written are generally recorded at the policy inception and are primarily earned on a pro rata basis over the terms of the policies for all products, usually 12 months. Premiums written include estimates in most of our insurance operations' lines of business. The amount of such insurance premium estimates included in premiums receivable and other assets at December 31, 2007 and 2006 was $50.1 million and $76.4 million, respectively. Such premium estimates are derived from multiple sources which include the historical experience of the underlying business, similar business and available industry information. Unearned premium reserves represent the portion of premiums written that relates to the unexpired terms of in-force insurance policies.

        Reinsurance premiums written include amounts reported by brokers and ceding companies, supplemented by our own estimates of premiums where reports have not been received or in cases where the amounts reported by brokers and ceding companies are adjusted to reflect management's best judgments and expectations. Premium estimates are derived from multiple sources which include our underwriters, the historical experience of the underlying business, similar business and available industry information. Premiums written are recorded based on the type of contracts we write. Premiums

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on our excess of loss and pro rata reinsurance contracts are estimated when the business is underwritten. For excess of loss contracts, the minimum premium, as defined in the contract, is generally recorded as an estimate of premiums written as of the inception date of the treaty. Estimates of premiums written under pro rata contracts are recorded in the period in which the underlying risks incept and are based on information provided by the brokers and the ceding companies. For multi-year reinsurance treaties which are payable in annual installments, generally, only the initial annual installment is included as premiums written at policy inception due to the ability of the reinsured to commute or cancel coverage during the term of the policy. The remaining annual installments are included as premiums written at each successive anniversary date within the multi-year term.

        Reinstatement premiums for our insurance and reinsurance operations are recognized at the time a loss event occurs, where coverage limits for the remaining life of the contract are reinstated under pre-defined contract terms. Reinstatement premiums, if obligatory, are fully earned when recognized. The accrual of reinstatement premiums is based on an estimate of losses and loss adjustment expenses, which reflects management's judgment, as described above in "—Reserves for Losses and Loss Adjustment Expenses."

        The amount of reinsurance premium estimates included in premiums receivable and the amount of related acquisition expenses by type of business were as follows at December 31, 2007 and 2006:

 
   December 31,
 
   2007
   2006
(U.S. dollars in thousands)
   Gross Amount
   Acquisition Expenses
   Net Amount
   Gross Amount
   Acquisition Expenses
   Net Amount
Casualty.    $ 171,876   ($ 47,127 ) $ 124,749   $ 191,842   ($ 52,382 ) $ 139,460
Property excluding property catastrophe     94,892     (23,918 )   70,974     110,996     (26,653 )   84,343
Marine and aviation     81,672     (22,492 )   59,180     76,167     (19,440 )   56,727
Other specialty     47,161     (11,185 )   35,976     85,886     (26,166 )   59,720
Property catastrophe     25,677     (4,346 )   21,331     23,079     (3,694 )   19,385
Other     1,157     (57 )   1,100     1,554     (101 )   1,453
   
 
 
 
 
 
  Total   $ 422,435   ($ 109,125 ) $ 313,310   $ 489,524   ($ 128,436 ) $ 361,088
   
 
 
 
 
 

        Premium estimates are reviewed by management at least quarterly. Such review includes a comparison of actual reported premiums to expected ultimate premiums along with a review of the aging and collection of premium estimates. Based on management's review, the appropriateness of the premium estimates is evaluated, and any adjustment to these estimates is recorded in the period in which it becomes known. Adjustments to premium estimates could be material and such adjustments could directly and significantly impact earnings favorably or unfavorably in the period they are determined because the estimated premium may be fully or substantially earned.

        A significant portion of amounts included as premiums receivable, which represent estimated premiums written, net of commissions, are not currently due based on the terms of the underlying contracts. Based on currently available information, management believes that the premium estimates included in premiums receivable will be collectible and, therefore, no provision for doubtful accounts has been recorded on the premium estimates at December 31, 2007.

        Reinsurance premiums assumed, irrespective of the class of business, are generally earned on a pro rata basis over the terms of the underlying policies or reinsurance contracts. Contracts and policies written on a "losses occurring" basis cover claims that may occur during the term of the contract or policy, which is typically 12 months. Accordingly, the premium is earned evenly over the term. Contracts which are written on a "risks attaching" basis cover claims which attach to the underlying insurance policies written during the terms of such contracts. Premiums earned on such contracts

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usually extend beyond the original term of the reinsurance contract, typically resulting in recognition of premiums earned over a 24-month period.

        Certain of our reinsurance contracts include provisions that adjust premiums or acquisition expenses based upon the experience under the contracts. Premiums written and earned, as well as related acquisition expenses, are recorded based upon the projected experience under such contracts.

        Retroactive reinsurance reimburses a ceding company for liabilities incurred as a result of past insurable events covered by the underlying policies reinsured. In certain instances, reinsurance contracts cover losses both on a prospective basis and on a retroactive basis and, accordingly, we bifurcate the prospective and retrospective elements of these reinsurance contracts and account for each element separately. Underwriting income generated in connection with retroactive reinsurance contracts is deferred and amortized into income over the settlement period while losses are charged to income immediately. Subsequent changes in estimated or actual cash flows under such retroactive reinsurance contracts are accounted for by adjusting the previously deferred amount to the balance that would have existed had the revised estimate been available at the inception of the reinsurance transaction, with a corresponding charge or credit to income.

        Acquisition expenses and other expenses that vary with, and are directly related to, the acquisition of business in our underwriting operations are deferred and amortized over the period in which the related premiums are earned. Acquisition expenses, net of ceding commissions received from unaffiliated reinsurers, consist primarily of commissions, brokerage and taxes paid to obtain our business. Other operating expenses also include expenses that vary with, and are directly related to, the acquisition of business. Deferred acquisition costs, which are based on the related unearned premiums, are carried at their estimated realizable value and take into account anticipated losses and loss adjustment expenses, based on historical and current experience, and anticipated investment income.

        For purposes of managing risk, we reinsure a portion of our exposures, paying to reinsurers a part of the premiums received on the policies we write, and we may also use retrocessional protection. Ceded premiums written represented approximately 29.9% of gross premiums written for 2007, compared to 29.5% for 2006 and 21.8% for 2005.

        The availability and cost of reinsurance and retrocessional protection is subject to market conditions, which are beyond our control. Although we believe that our insurance subsidiaries have been successful in obtaining reinsurance protection, it is not certain that we will be able to obtain adequate protection at cost effective levels. As a result of such market conditions and other factors, we may not be able to successfully mitigate risk through reinsurance and retrocessional arrangements. Further, we are subject to credit risk with respect to our reinsurers and retrocessionaires because the ceding of risk to reinsurers and retrocessionaires does not relieve us of our liability to the clients or companies we insure or reinsure. We are also subject to risks based upon the possibility that loss payments could occur earlier than the receipt of related reinsurance recoverables. Our failure to establish adequate reinsurance or retrocessional arrangements or the failure of our existing reinsurance or retrocessional arrangements to protect us from overly concentrated risk exposure could adversely affect our financial condition and results of operations.

        We monitor the financial condition of our reinsurers and attempt to place coverages only with substantial, financially sound carriers. At December 31, 2007 and 2006, approximately 88.5% and 92.3%, respectively, of our reinsurance recoverables on paid and unpaid losses (not including prepaid reinsurance premiums) of $1.74 billion and $1.67 billion, respectively, were due from carriers which had an A.M. Best rating of "A-" or better. At December 31, 2007 and 2006, the largest reinsurance recoverables from any one carrier were less than 5.2% and 5.1%, respectively, of our total shareholders' equity.

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        The following table details our reinsurance recoverables at December 31, 2007:

 
   % of Total
   A.M. Best Rating(1)
Everest Reinsurance Company   12.1 % A+
Flatiron Re Ltd.(2)   8.8 % NR
Munich Reinsurance America, Inc.    6.9 % A+
Lloyd's of London syndicates(3)   6.7 % A
Allied World Assurance Company Ltd.    5.8 % A
Odyssey America Reinsurance Corporation(4)   5.1 % A
Swiss Reinsurance America Corporation   5.0 % A+
Federal Insurance Company   4.1 % A++
ACE Property & Casualty Insurance Company   3.4 % A+
Transatlantic Reinsurance Company   3.3 % A+
Platinum Underwriters Reinsurance Inc.    2.9 % A
GE Frankona Reinsurance Ltd.    2.7 % A
Sentry Insurance a Mutual Company(5)   2.3 % A+
All other(6)   30.9 %  
   
   
  Total   100.0 %  
   
   

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Companies rated "A-" or better   28.2 %
Companies not rated(7)   2.7 %
   
 
Total   30.9 %
   
 

        If the financial condition of our reinsurers or retrocessionaires deteriorates, resulting in an impairment of their ability to make payments, we will provide for probable losses resulting from our inability to collect amounts due from such parties, as appropriate. We evaluate the credit worthiness of all the reinsurers to which we cede business. If our analysis indicates that there is significant uncertainty regarding the collectibility of amounts due from reinsurers, managing general agents, brokers and other clients, we will record a provision for doubtful accounts.

        At December 31, 2007, approximately 78.8% of premiums receivable of $729.6 million represented amounts not yet due, while amounts in excess of 90 days overdue were 2.9% of the total. At December 31, 2006, approximately 83.5% of premiums receivable of $750.0 million represented amounts not yet due, while amounts in excess of 90 days overdue were 1.9% of the total. Approximately 37.4% of the $132.3 million of paid losses and loss adjustment expenses recoverable were in excess of 90 days overdue at December 31, 2007 (a significant portion of such overdue amounts were collected in February 2008), compared to 19.6% of the $122.1 million of paid losses and loss adjustment expenses recoverable at December 31, 2006. At December 31, 2007 and 2006, our reserves for doubtful accounts were approximately $10.5 million and $12.0 million, respectively.

        We are also subject to credit risk from our alternative market products, such as rent-a-captive risk-sharing programs, which allow a client to retain a significant portion of its loss exposure without the administrative costs and capital commitment required to establish and operate its own captive. In certain of these programs, we participate in the operating results by providing excess reinsurance coverage and earn commissions and management fees. In addition, we write program business on a risk-sharing basis with managing general agents or brokers, which may be structured with commissions which are contingent on the underwriting results of the program. While we attempt to obtain collateral from such parties in an amount sufficient to guarantee their projected financial obligations to us, there is no guarantee that such collateral will be sufficient to secure their actual ultimate obligations.

        Deferred income taxes reflect the expected future tax consequences of temporary differences between the carrying amounts of assets and liabilities for financial reporting purposes and amounts used for income tax purposes. A valuation allowance is recorded if it is more likely than not that some or all of a deferred income tax asset may not be realized. We consider future taxable income and feasible tax planning strategies in assessing the need for a valuation allowance. In the event we determine that we will not be able to realize all or part of our deferred income tax assets in the future, an adjustment to the deferred income tax assets would be charged to income in the period in which such determination is made. In addition, if we subsequently assess that the valuation allowance is no longer needed, a benefit would be recorded to income in the period in which such determination is made.

        We recognize a tax benefit where we conclude that it is more likely than not that the tax benefit will be sustained on audit by the taxing authority based solely on the technical merits of the associated tax position. If the recognition threshold is met, we recognize a tax benefit measured at the largest

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amount of the tax benefit that, in our judgment, is greater than 50% likely to be realized. We record interest and penalties related to unrecognized tax benefits in the provision for income taxes.

        We currently classify all of our fixed maturity investments, short-term investments and other investments as "available for sale" and, accordingly, they are carried at estimated fair value. The fair value of fixed maturity securities is generally determined from quotations received from nationally recognized pricing services, or when such prices are not available, by reference to broker or underwriter bid indications. Short-term investments comprise securities due to mature within one year of the date of issue. Short-term investments include certain cash equivalents which are part of our investment portfolios under the management of external and internal investment managers. Other investments are carried at estimated fair value. Fair value is initially considered to be equal to the cost of such investment until the investment is revalued based on substantive events or other factors which could indicate a diminution or appreciation in value.

        Other investments are classified as "available for sale" and include alternative investments, which are funds with underlying ownership structures that may be limited partnerships ("LPs") or limited liability companies ("LLCs"), equity securities such as investments in mutual funds and privately held securities. For those investments in which the underlying ownership structure is an LP or an LLC (i.e., when the LLC meets specific criteria requiring it to be treated similar to an LP) we use the equity method to account for such investments. Under the equity method, investments are initially recorded at cost and are subsequently adjusted for changes in our proportionate share of net income or loss or other changes in capital of the investee. Changes in the carrying value of such investments are recorded in net investment income or other income. Investments in equity securities are carried at estimated fair value in accordance with SFAS No. 115. The estimated fair value of investments in privately held securities, other than those carried under the equity method, is initially equal to the cost of such investments until the investments are revalued based principally on substantive events or other factors which could indicate a diminution or appreciation in value, such as an arm's-length third party transaction justifying an increased valuation or adverse development of a significant nature requiring a write-down.

        In accordance with SFAS No. 115, "Accounting for Certain Investments in Debt and Equity Securities," FASB Staff Position Nos. FAS 115-1 and FAS 124-1, "The Meaning of Other-Than-Temporary Impairment and Its Application to Certain Investments" and Securities and Exchange Commission Staff Accounting Bulletin No. 59, "Other-Than-Temporary Impairment of Certain Investments in Debt and Equity Securities," we review our investments each quarter to determine whether a decline in fair value below the amortized cost basis is other-than-temporary. Our process for identifying declines in the fair value of investments that are other-than-temporary involves consideration of several factors. These factors include (i) the time period in which there has been a significant decline in value, (ii) an analysis of the liquidity, business prospects and overall financial condition of the issuer, (iii) the significance of the decline and (iv) our intent and ability to hold the investment for a sufficient period of time for the value to recover. Where our analysis of the above factors results in the conclusion that declines in fair values are other-than-temporary, the cost of the securities is written down to fair value and is reflected as a realized loss. In periods subsequent to the recognition of an other-than-temporary impairment on fixed maturities, we account for such securities as if they had been purchased on the measurement date of the other-than-temporary impairment and the provision for other-than-temporary impairment (reflected as a discount or reduced premium based on the new cost basis) is amortized into net investment income over the remaining life of the fixed maturities, or until such securities are sold.

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        With respect to securities where the decline in value is determined to be temporary because we concluded that the investment was impaired for a minor length of time or to a minor extent and the security's value is not written down, a subsequent decision may be made to sell that security and realize a loss. Such sale would not contradict our determination that the decline was temporary because subsequent decisions to sell a security are made within the context of overall risk management, new information and the assessment of such security's value relative to comparable securities. While our internal and external investment managers may, at a given point in time, believe the preferred course of action is to hold securities until such losses are recovered, the dynamic nature of portfolio management may result in a subsequent decision by us to sell the security and realize the loss, based upon a change in market and other factors discussed above. We believe these subsequent decisions are consistent with the classification of our investment portfolio as "available for sale." See note 7, "Investment Information," of the notes accompanying our consolidated financial statements.

        Under SFAS No. 133, "Accounting for Derivative Instruments and Hedging Activities" ("SFAS No. 133"), as amended on January 1, 2001, all derivative financial instruments, including embedded derivative instruments, are required to be recognized as either assets or liabilities in the consolidated balance sheets and measured at fair value. The accounting for gains and losses associated with changes in the fair value of a derivative and the effect on the consolidated financial statements depends on whether it has been designated and qualifies as part of a hedging relationship and whether the hedge is highly effective in achieving offsetting changes in the fair value of the asset or liability hedged.

        Our investment strategy allows for the use of derivative instruments. We utilize various derivative instruments such as futures contracts to enhance investment performance, replicate investment positions or manage market exposures and duration risk that would be allowed under our investment guidelines if implemented in other ways. Pursuant to SFAS No. 133, these instruments, which have no hedging designation, are recognized as assets and liabilities in our balance sheet at fair value and changes in fair value are included in net realized gains and losses in our results of operations. See note 7, "Investment Information—Investment-Related Derivatives," of the notes accompanying our consolidated financial statements for more information about our use of derivative instruments.

        On January 1, 2006, we adopted the fair value method of accounting for share-based awards using the modified prospective method of transition as described in Financial Accounting Standards Board ("FASB") Statement No. 123 (revised 2004), "Share-Based Payment" ("SFAS No. 123(R)"). Under SFAS No.123(R), the estimated grant date fair value adjusted for assumed forfeitures of share-based compensation related to stock option awards is recognized as compensation expense over the requisite service period of the grant. Under the fair value method of accounting pursuant to SFAS No. 123(R), the fair value of restricted share and unit awards is measured by the grant date price of our shares. No value is attributed to awards that employees forfeit because they fail to satisfy vesting conditions. As such, the number of shares granted is reduced by assumed forfeitures and adjusted based on actual forfeitures until vesting. Such expense is amortized over the requisite service period of the related awards. For awards granted to retirement-eligible employees where no service is required for the employee to retain the award, the grant date fair value is immediately recognized as compensation cost at the grant date because the employee is able to retain the award without continuing to provide service. For employees near retirement eligibility, attribution of compensation cost is over the period from the grant date to the retirement eligibility date. The share-based compensation expense associated with awards that have graded vesting features and vest based on service conditions only (i) granted after the effective date of adoption is calculated on a straight-line basis over the requisite service periods of the related awards and (ii) granted prior to the effective date of adoption and that remain unvested as of the date of adoption is calculated on a graded-vesting basis as prescribed under FASB Interpretation No. 28, "Accounting for Stock Appreciation Rights and Other Variable Stock Option or

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Award Plans—an interpretation of APB Opinions No. 15 and 25," over the remaining requisite service periods of the related awards.

        Under the modified prospective method of transition, compensation expense is recognized beginning with the effective date of adoption for all share-based payments (i) granted after the effective date of adoption and (ii) granted prior to the effective date of adoption and that remain unvested on the date of adoption. Under the modified prospective method of transition, we are not required to restate our prior period financial statements to reflect expensing of share-based compensation under SFAS No.123(R). Therefore, the results for 2007 and 2006 are not comparable to results for 2005 period.

        Under SFAS No. 123(R), we use the Black-Scholes option pricing model to estimate the fair value of the share-based option awards as of the grant date. The Black-Scholes model, by its design, is highly complex, and requires judgment in determining key data inputs including estimating the risk free interest rate, expected life of the option and expected volatility rate. In addition, judgment is also required in estimating the amount of share-based awards that are expected to be forfeited. The primary data inputs with the greatest degree of judgment are the estimated lives of the share-based awards and the estimated volatility of our stock price. The Black-Scholes model is highly sensitive to changes in these two data inputs. In our process for estimating the fair value of stock options granted, we believe that we have made a good faith fair value estimate in accordance with the provisions of SFAS No. 123(R) as well as guidance from the SEC as contained in Staff Accounting Bulletin No. 107 in a way that is designed to take into account the assumptions that underlie the instrument's value that marketplace participants would reasonably make. If actual results differ significantly from these estimates, share-based compensation expense and our results of operations could be materially impacted.

        See note 2(l), "Significant Accounting Policies—Share-Based Compensation," of the notes accompanying our consolidated financial statements for more information about the adoption of SFAS No. 123(R).

        We have reclassified the presentation of certain prior year information to conform to the current presentation. Such reclassifications had no effect on our net income, shareholders' equity or cash flows.

        See note 2(p), "Significant Accounting Policies—Recent Accounting Pronouncements," of the notes accompanying our consolidated financial statements.

Results of Operations

Comparison of Years Ended December 31, 2007 and 2006

        The following table sets forth net income available to common shareholders and per share data:

 
   Years Ended
December 31,
(U.S. dollars in thousands, except share data)
   2007
   2006
Net income available to common shareholders   $ 832,099   $ 692,559
   
 
Diluted net income per common share   $ 11.28   $ 9.08
   
 
Diluted weighted average common shares and common share equivalents outstanding     73,762,419     76,246,725
   
 

        Net income available to common shareholders was $832.1 million for 2007, compared to $692.6 million for 2006. The improvement in our results of operations was primarily due to growth in

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investment income and a low level of catastrophic activity, as discussed in "—Segment Information" below. Our net income available to common shareholders for 2007 represented a 23.9% annualized return on average common equity, compared to 24.1% for 2006.

        The decrease in diluted average shares outstanding from 2006 to 2007 was primarily due to the weighted impact of share repurchases during 2007, partially offset by increases in the dilutive effects of stock options and nonvested restricted stock calculated using the treasury stock method and the exercise of stock options. Under the treasury stock method, the dilutive impact of options and nonvested stock on diluted weighted average shares outstanding increases as the market price of our common shares increases.

        We determined our reportable operating segments using the management approach described in SFAS No. 131 "Disclosures about Segments of an Enterprise and Related Information," as further detailed in note 3, "Segment Information," of the notes accompanying our consolidated financial statements. Management measures segment performance based on underwriting income or loss, which includes the excess or deficiency of net premiums earned for each reporting period over the combined total of expenses and losses incurred during the same period.

        The following table sets forth our insurance segment's underwriting results:

 
   Years Ended
December 31,
  
(U.S. dollars in thousands)
   2007
   2006
  
Gross premiums written   $ 2,660,302   $ 2,624,757  
Net premiums written     1,717,548     1,652,056  
Net premiums earned   $ 1,702,343   $ 1,600,854  
Fee income     5,063     5,085  
Losses and loss adjustment expenses     (1,077,769 )   (1,017,263 )
Acquisition expenses, net     (201,703 )   (175,740 )
Other operating expenses     (276,388 )   (249,637 )
   
 
 
Underwriting income   $ 151,546   $ 163,299  
   
 
 

Underwriting Ratios
 
 
 
 
 
 
 
Loss ratio     63.3 %   63.5 %
Acquisition expense ratio(1)     11.7 %   10.8 %
Other operating expense ratio     16.2 %   15.6 %
   
 
 
Combined ratio     91.2 %   89.9 %
   
 
 

        Underwriting Income.    The insurance segment's underwriting income was $151.5 million for 2007, compared to $163.3 million for 2006. The combined ratio for the insurance segment was 91.2% for 2007, compared to 89.9% for 2006. The components of the insurance segment's underwriting income are discussed below.

        Premiums Written.    Gross premiums written by the insurance segment were $2.66 billion for 2007, compared to $2.62 billion for 2006, and ceded premiums written were 35.4% of gross premiums written for 2007, compared to 37.1% for 2006. Net premiums written by the insurance segment were $1.72 billion for 2007, compared to $1.65 billion for 2006. Contributing to the higher level of net

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premiums written in 2007 were increases in professional liability business, as a result of growth in policies written, a higher level of travel and accident business and a decrease in the usage of reinsurance, national accounts casualty business and excess workers' compensation and employers' liability business produced by Wexford (included in 'other'). During the 2007 fourth quarter, we completed the acquisition of the operations of Wexford, including the renewal rights of the subject business, through an asset purchase. This growth was partially offset by a continued reduction in U.S. primary casualty business and surety business in response to increasing competition and market conditions. For information regarding net premiums written by major line of business and geographic location, refer to note 3, "Segment Information," of the notes accompanying our consolidated financial statements.

        Net Premiums Earned.    Net premiums earned for the insurance segment were $1.7 billion for 2007, compared to $1.6 billion for 2006, and generally reflect changes in net premiums written over the previous five quarters, including the mix and type of business written.

        Losses and Loss Adjustment Expenses.    Insurance segment losses and loss adjustment expenses incurred for 2007 were $1.08 billion, or 63.3% of net premiums earned, compared to $1.02 billion, or 63.5% of net premiums earned, for 2006. The 2007 loss ratio reflected a 0.7 point reduction related to estimated net favorable development in prior year loss reserves, compared to a 0.5 point reduction in 2006. Prior to 2005, the insurance segment's reserving method relied heavily on industry data. In 2005, the insurance segment began to give a relatively small amount of weight to its own experience. As a result, the insurance segment reduced loss selections for some lines, in particular those written on a claims-made basis and for which it now believes it has a reasonable level of credible data. The insurance segment's net favorable development in 2007 and 2006 was primarily due to reductions in reserves in medium-tailed and long-tailed lines of business resulting from such changes, partially offset by adverse development of $33.3 million from short-tail lines which primarily resulted from higher than expected claims development. The net favorable development was partially offset by an increase in acquisition expenses of $9.5 million, primarily due to sliding scale arrangements on certain policies..

        For a discussion of the reserves for losses and loss adjustment expenses, please refer to the section above entitled "Critical Accounting Policies, Estimates and Recent Accounting Pronouncements—Reserves for Losses and Loss Adjustment Expenses."

        Underwriting Expenses.    The underwriting expense ratio for the insurance segment was 27.9% in 2007, compared to 26.4% for 2006. The acquisition expense ratio is influenced by, among other things, (1) the amount of ceding commissions received from unaffiliated reinsurers, (2) the amount of business written on a surplus lines (non-admitted) basis and (3) mix of business. The acquisition expense ratio was 11.7% for 2007, compared to 10.8% for 2006. The acquisition expense ratio in 2007 reflects changes in the form of reinsurance ceded and the mix of business and also included 0.5 points related to favorable prior year loss development, while the 2006 period included a decrease in surety profit commissions which increased the 2006 acquisition expense ratio by 0.5 points. The insurance segment's other operating expense ratio was 16.2% for 2007, compared to 15.6% for 2006. The higher operating expense ratio in 2007 compared to 2006 was primarily due to growth in compensation-related expenses without an attendant growth in net premiums earned.

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        The following table sets forth our reinsurance segment's underwriting results:

 
   Years Ended
December 31,
  
(U.S. dollars in thousands)
   2007
   2006
  
Gross premiums written   $ 1,517,645   $ 1,703,796  
Net premiums written     1,184,388     1,365,362  
Net premiums earned   $ 1,242,307   $ 1,480,811  
Fee income     2,473     4,729  
Losses and loss adjustment expenses     (566,401 )   (773,286 )
Acquisition expenses, net     (278,828 )   (368,171 )
Other operating expenses     (81,059 )   (53,533 )
   
 
 
Underwriting income   $ 318,492   $ 290,550  
   
 
 

Underwriting Ratios
 
 
 
 
 
 
 
Loss ratio     45.6 %   52.2 %
Acquisition expense ratio     22.4 %   24.9 %
Other operating expense ratio     6.5 %   3.6 %
   
 
 
Combined ratio     74.5 %   80.7 %
   
 
 

        Underwriting Income.    The reinsurance segment's underwriting income was $318.5 million for 2007, compared to $290.6 million for 2006. The combined ratio for the reinsurance segment was 74.5% for 2007, compared to 80.7% for 2006. The components of the reinsurance segment's underwriting income are discussed below.

        Premiums Written.    Gross premiums written by the reinsurance segment were $1.52 billion in 2007, compared to $1.7 billion for 2006. Gross premiums written for 2007 reflects a lower level of casualty, other specialty and non-catastrophe exposed property business which was in response to continued competition and resulted in either non-renewals or lower shares written by the reinsurance segment. Such reductions were partially offset by continued growth in international property and marine lines, due to higher rates and an increase in exposure. Catastrophe-exposed property and marine lines have continued to provide attractive opportunities in the wake of the 2005 storms.

        Ceded premiums written by the reinsurance segment were 22.0% of gross premiums written for 2007, compared to 19.9% for 2006. The higher ceded percentage in 2007 primarily resulted from the $311.3 million of premiums written ceded by Arch Re Bermuda to Flatiron Re Ltd. ($282.2 million on an earned basis), compared to $273.2 million in 2006 ($157.4 million on an earned basis). At December 31, 2007, $144.9 million of premiums ceded to Flatiron Re Ltd. were unearned. The attendant premiums earned, losses incurred and acquisition expenses will primarily be reflected in the reinsurance segment's results in the first half of 2008.

        Net premiums written by the reinsurance segment were $1.18 billion for 2007, compared to $1.37 billion for 2006. Net premiums written for 2007 reflects the lower level of international casualty business noted above, which more than offset growth in international property and marine lines, net of the amounts ceded to Flatiron Re Ltd. For information regarding net premiums written by major line and type of business and geographic location, refer to note 3, "Segment Information," of the notes accompanying our consolidated financial statements.

        Net Premiums Earned.    Net premiums earned for our reinsurance segment were $1.24 billion for 2007, compared to $1.48 billion for 2006, and generally reflect changes in net premiums written over the previous five quarters, including the mix and type of business written.

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        Losses and Loss Adjustment Expenses.    Reinsurance segment losses and loss adjustment expenses incurred for 2007 were $566.4 million, or 45.6% of net premiums earned, compared to $773.3 million, or 52.2% of net premiums earned, for 2006. The 2007 loss ratio reflected a 13.9 point reduction related to estimated net favorable development in prior year loss reserves, compared to a 4.6 point reduction in 2006. Of the 2007 net favorable development in the reinsurance segment, a significant portion came from short-tail lines and resulted from better than anticipated loss emergence. In addition, the reinsurance segment's 2007 results included approximately 4.3 points related to 2007 catastrophe losses, while the 2006 results included 3.1 points related to 2006 catastrophe losses. The reinsurance segment's 2007 loss ratio also reflects an increase in expected loss ratios across a number of lines of business, primarily due to premium rate decreases and loss cost trends, and changes in the mix of business.

        In its reserving process in 2002 and 2003, the reinsurance segment recognized that there is a possibility that the assumptions made could prove to be inaccurate due to several factors primarily related to the start up nature of its operations. Due to the availability of additional data, and based on reserve analyses, it was determined that it was no longer necessary to continue to include such factors in the reserving process in 2004. Following reserve reviews, and based on the level of claims activity reported to date, the reinsurance segment has reduced the amount it had recorded in 2002 and 2003 by $10.6 million in 2007 and $7.7 million in 2006. Such amounts are reflected in the prior year development indicated above.

        The net favorable development on prior year loss reserves in both periods was partially offset by increased acquisition expenses, primarily as a result of the commutation of certain treaties. Such activity resulted in an increase to the acquisition expense ratio of approximately 1.5 points in 2007, compared to 0.5 points in 2006. The remainder of the change in the loss ratio for 2007, compared to 2006, resulted from better results recorded in the reinsurance segment's property lines of business and changes in their mix of business.

        For a discussion of the reserves for losses and loss adjustment expenses, please refer to the section above entitled "Critical Accounting Policies, Estimates and Recent Accounting Pronouncements—Reserves for Losses and Loss Adjustment Expenses."

        Underwriting Expenses.    The underwriting expense ratio for the reinsurance segment was 28.9% for 2007, compared to 28.5% for 2006. The acquisition expense ratio for 2007 was 22.4%, compared to 24.9% for 2006. The acquisition expense ratio is influenced by, among other things, the mix and type of business written and earned and the level of ceding commission income. The acquisition expense ratio for 2007 included 1.5 points related to favorable prior year loss development, compared to 0.5 points in 2006. In addition, the reinsurance segment's results included commission income (in excess of the reimbursement of direct acquisition expenses) on the quota-share reinsurance treaty with Flatiron Re Ltd., which reduced the acquisition expense ratio by 3.1 points in 2007, compared to 1.6 points in 2006. The reinsurance segment's other operating expense ratio was 6.5% for 2007, compared to 3.6% for 2006. The higher ratio in 2007 primarily resulted from expenses related to the reinsurance segment's property facultative reinsurance operation, which commenced operations during the 2007 second quarter, and a lower level of net premiums earned.

        Net investment income was $463.1 million for 2007, compared to $380.2 million for 2006. The increase in net investment income in 2007 resulted from a higher level of average invested assets primarily generated by cash flows from operations. In addition, an increase in the pre-tax investment income yield to 4.88% for 2007 from 4.71% for 2006 contributed to the growth in net investment income. These yields were calculated based on amortized cost. The increase in the pre-tax investment yield primarily resulted from higher interest rates embedded in the investment portfolio as the portfolio's average credit quality remained near the AAA level and the effective duration only

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increased marginally. Yields on future investment income may vary based on financial market conditions, investment allocation decisions and other factors.

        Following is a summary of net realized gains (losses):

 
   Years Ended
December 31,
  
(U.S. dollars in thousands)
   2007
   2006
  
Fixed maturities   $ 38,611   ($ 27,379 )
Other investments     847     4,186  
Other     (11,317 )   3,756  
   
 
 
Total   $ 28,141   ($ 19,437 )
   
 
 

        Total return on our portfolio under management for 2007 was 6.52%, compared to 5.24% for 2006. Total return is calculated on a pre-tax basis and before investment expenses. The higher total return in 2007 compared to 2006 was primarily due to movements in interest rates and foreign exchange rates during the periods. For 2007, net realized gains on our fixed maturities of $38.6 million included a provision of $28.1 million for declines in the fair value of investments held in our available for sale portfolio which were considered to be other-than-temporary, based on reviews performed during 2007. For 2006, net realized losses on our fixed maturities of $27.4 million included a provision of $31.6 million for declines in the fair value of investments held in our available for sale portfolio which were considered to be other-than-temporary, based on reviews performed during 2006. In periods subsequent to the recognition of an other-than-temporary impairment on fixed maturities, we account for such securities as if they had been purchased on the measurement date of the other-than temporary impairment and the provision for the other-than-temporary impairment (reflected as a discount or reduced premium based on the new cost basis) is amortized into net investment income over the remaining life of the fixed maturities, or until such securities are sold. The declines in fair value on such securities were primarily due to the prevailing interest rate, credit and foreign exchange environments. The balance of net realized gains on our fixed maturities in 2007 and 2006 resulted from the sale of securities. For the 2007 and 2006 periods, net realized gains or losses from the sale of fixed maturities primarily resulted from our decisions to reduce credit exposure, changes in duration targets, relative value determinations and sales related to rebalancing the portfolio.

        Other expenses, which are included in our other operating expenses and part of our corporate and other segment (non-underwriting), were $30.7 million for 2007, compared to $29.1 million for 2006. Such amounts primarily represent certain holding company costs necessary to support our worldwide insurance and reinsurance operations, share based compensation expense and costs associated with operating as a publicly traded company.

        As required by the provisions of SFAS 123(R), we recorded pre-tax share-based compensation expense related to stock options of $9.0 million in 2007, compared to $9.2 million in 2006. See note 13, "Share Capital," of the notes accompanying our consolidated financial statements and "Critical Accounting Policies, Estimates and Recent Accounting Policies—Share-Based Compensation" for more information about the adoption of SFAS No. 123(R).

        Net foreign exchange losses for 2007 of $44.0 million consisted of net unrealized losses of $48.8 million and net realized gains of $4.8 million, compared to net foreign exchange losses of

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$23.9 million for 2006, which consisted of net unrealized losses of $27.3 million and net realized gains of $3.4 million. For the 2007 and 2006 periods, the net unrealized foreign exchange gains or losses recorded were largely offset by changes in the value of our investments held in foreign currencies. Net unrealized foreign exchange gains or losses result from the effects of revaluing our net insurance liabilities required to be settled in foreign currencies at each balance sheet date. The net foreign exchange losses in 2007 and 2006 primarily resulted from a weakening of the U.S. Dollar. We hold investments in foreign currencies which are intended to mitigate its exposure to foreign currency fluctuations in its net insurance liabilities. However, changes in the value of such investments due to foreign currency rate movements are reflected as a direct increase or decrease to shareholders' equity and are not included in the statement of income. For the 2007 and 2006 periods, the net unrealized foreign exchange gains or losses recorded by us were largely offset by changes in the value of our investments held in foreign currencies.

        ACGL changed its legal domicile from the United States to Bermuda in November 2000. Under current Bermuda law, we are not obligated to pay any taxes in Bermuda based upon income or capital gains. We have received a written undertaking from the Minister of Finance in Bermuda under the Exempted Undertakings Tax Protection Act of 1966 that in the event legislation is enacted in Bermuda imposing tax computed on profits, income, gain or appreciation on any capital asset, or tax in the nature of estate duty or inheritance tax, such tax will not be applicable to us or our operations until March 28, 2016.

        ACGL will be subject to U.S. federal income tax only to the extent that it derives U.S. source income that is subject to U.S. withholding tax or income that is effectively connected with the conduct of a trade or business within the U.S. and is not exempt from U.S. tax under an applicable income tax treaty. ACGL will be subject to a withholding tax on dividends from U.S. investments and interest from certain U.S. taxpayers. ACGL does not consider itself to be engaged in a trade or business within the U.S. and, consequently, does not expect to be subject to direct U.S. income taxation. However, because there is uncertainty as to the activities which constitute being engaged in a trade or business within the United States, there can be no assurances that the U.S. Internal Revenue Service will not contend successfully that ACGL or its non-U.S. subsidiaries are engaged in a trade or business in the United States. If ACGL or any of its non-U.S. subsidiaries were subject to U.S. income tax, ACGL's shareholders' equity and earnings could be materially adversely affected. ACGL has subsidiaries and branches that operate in various jurisdictions around the world that are subject to tax in the jurisdictions in which they operate. The significant jurisdictions in which ACGL's subsidiaries and branches are subject to tax are the United States, United Kingdom, Canada, Switzerland, Germany and Denmark. See "Risk Factors—Risks Relating to Taxation" and "Business—Tax Matters."

        The income tax provision on income before income taxes resulted in an effective tax rate of 1.8% for 2007, compared to 3.6% for 2006. Our effective tax rate fluctuates from year to year consistent with the relative mix of income reported by jurisdiction due primarily to the varying tax rates in each jurisdiction. A significant portion of our catastrophe-exposed property business is written by a Bermuda-based subsidiary. As a result, on a relative basis, our effective tax rate is likely to be favorably affected in periods that have a low level of catastrophic losses incurred and adversely impacted in periods with significant catastrophic claims activity. We currently estimate that our comparable income tax provision in 2008 will result in an effective tax rate of approximately 2.0% to 4.0%, although no assurances can be given to that effect. See note 9, "Income Taxes," of the notes accompanying our consolidated financial statements for a reconciliation of the difference between the provision for income taxes and the expected tax provision at the weighted average statutory tax rate for 2007, 2006 and 2005, along with a description of net operating loss carryforwards and other tax items.

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Comparison of Years Ended December 31, 2006 and 2005

        The following table sets forth net income available to common shareholders and per share data:

 
   Years Ended
December 31,
(U.S. dollars in thousands, except share data)
   2006
   2005
Net income available to common shareholders   $ 692,559   $ 256,486
   
 
Diluted net income per common share   $ 9.08   $ 3.43
   
 
Diluted weighted average common shares and common share equivalents outstanding     76,246,725     74,709,858
   
 

        Net income available to common shareholders was $692.6 million for 2006, compared to $256.5 million for 2005. The improvement in our results of operations was primarily due to a lower level of catastrophic activity in 2006, as discussed in "—Segment Information" below, and growth in investment income. Our net income available to common shareholders for 2006 represented a 24.1% annualized return on average common equity, compared to 10.9% for 2005.

        The increase in diluted average shares outstanding from 2005 to 2006 was due, in part, to increases in the dilutive effects of stock options and nonvested restricted stock calculated using the treasury stock method and the exercise of stock options. Under the treasury stock method, the dilutive impact of options and nonvested stock on diluted weighted average shares outstanding increases as the market price of our common shares increases.

Segment Information

        The following table sets forth our insurance segment's underwriting results:

 
   Years Ended
December 31,
  
(U.S. dollars in thousands)
   2006
   2005
  
Gross premiums written   $ 2,624,757   $ 2,325,632  
Net premiums written     1,652,056     1,481,300  
Net premiums earned   $ 1,600,854   $ 1,392,114  
Fee income     5,085     5,332  
Losses and loss adjustment expenses     (1,017,263 )   (949,996 )
Acquisition expenses, net     (175,740 )   (137,804 )
Other operating expenses     (249,637 )   (221,934 )
   
 
 
Underwriting income   $ 163,299   $ 87,712  
   
 
 

Underwriting Ratios
 
 
 
 
 
 
 
Loss ratio     63.5 %   68.2 %
Acquisition expense ratio(1)     10.8 %   9.7 %
Other operating expense ratio     15.6 %   15.9 %
   
 
 
Combined ratio     89.9 %   93.8 %
   
 
 

        Underwriting Income.    The insurance segment's underwriting income was $163.3 million for 2006, compared to $87.7 million for 2005. The combined ratio for the insurance segment was 89.9% for 2006,

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compared to 93.8% for 2005. The components of the insurance segment's underwriting income are discussed below.

        Premiums Written.    Gross premiums written by the insurance segment were $2.62 billion for 2006, compared to $2.33 billion for 2005, and ceded premiums written were 37.1% of gross premiums written for 2006, compared to 36.3% for 2005. Net premiums written by the insurance segment were $1.65 billion for 2006, compared to $1.48 billion for 2005. Roughly half of the increase was in worldwide property business, primarily as a result of rate increases which were tempered by higher reinsurance costs. The balance of the growth was generated from increases in professional liability business, as a result of growth in policies written and a decrease in the usage of reinsurance in 2006 business, construction business, primarily due to growth in large deductible construction accounts, surety business, and in executive assurance business. This growth was partially offset by a reduction in U.S. primary casualty business in response to increasing competition. For information regarding net premiums written by major line of business and geographic location, refer to note 3, "Segment Information," of the notes accompanying our consolidated financial statements.

        Net Premiums Earned.    Net premiums earned for the insurance segment were $1.6 billion for 2006, compared to $1.39 billion for 2005, and generally reflect changes in net premiums written over the previous five quarters, including the mix and type of business written.

        Losses and Loss Adjustment Expenses.    Insurance segment losses and loss adjustment expenses incurred for 2006 were $1.02 billion, or 63.5% of net premiums earned, compared to $950.0 million, or 68.2% of net premiums earned, for 2005. The insurance segment's results for 2006 included several large individual risk losses in the 2006 fourth quarter totaling $36.6 million, or 2.3 points, while 2005 included $119.8 million, or 8.6 points, related to Hurricanes Dennis, Emily, Katrina, Rita and Wilma and the European Floods. In addition, the 2006 loss ratio reflected a 0.5 point reduction related to estimated net favorable development in prior year loss reserves, compared to a 2.0 point reduction in 2005. Prior to 2005, the insurance segment's reserving method relied heavily on industry data. In 2005, the insurance segment began to give a relatively small amount of weight to its own experience. As a result, the insurance segment reduced loss selections for some lines, in particular those written on a claims-made basis and for which it now believes it has a reasonable level of credible data. The insurance segment's net favorable development in 2006 and 2005 was primarily due to reductions in reserves in medium-tailed and long-tailed lines of business resulting from such changes, partially offset by adverse development from short-tail lines which was primarily resulted from development on the 2005 catastrophic events.

        For a discussion of the reserves for losses and loss adjustment expenses, please refer to the section above entitled "Critical Accounting Policies, Estimates and Recent Accounting Pronouncements—Reserves for Losses and Loss Adjustment Expenses."

        Underwriting Expenses.    The underwriting expense ratio for the insurance segment was 26.4% in 2006, compared to 25.6% for 2005. The acquisition expense ratio was 10.8% for 2006, compared to 9.7% for 2005. As a result of the large individual risk losses noted above, the insurance segment reduced profit commissions that it had recorded previously by $7.7 million, or 0.5 points of the acquisition expense ratio. The remainder of the increase in the acquisition expense ratio was primarily due to changes in the mix of business. The insurance segment's other operating expense ratio was 15.6% for 2006, compared to 15.9% for 2005.

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        The following table sets forth our reinsurance segment's underwriting results:

 
   Years Ended
December 31,
  
(U.S. dollars in thousands)
   2006
   2005
  
Gross premiums written   $ 1,703,796   $ 1,750,839  
Net premiums written     1,365,362     1,657,472  
Net premiums earned   $ 1,480,811   $ 1,585,602  
Fee income     4,729     5,035  
Losses and loss adjustment expenses     (773,286 )   (1,051,953 )
Acquisition expenses, net     (368,171 )   (442,116 )
Other operating expenses     (53,533 )   (52,192 )
   
 
 
Underwriting income   $ 290,550   $ 44,376  
   
 
 
Underwriting Ratios              
Loss ratio     52.2 %   66.3 %
Acquisition expense ratio     24.9 %   27.9 %
Other operating expense ratio     3.6 %   3.3 %
   
 
 
Combined ratio     80.7 %   97.5 %
   
 
 

        Underwriting Income.    The reinsurance segment's underwriting income was $290.6 million for 2006, compared to $44.4 million for 2005. The combined ratio for the reinsurance segment was 80.7% for 2006, compared to 97.5% for 2005. The components of the reinsurance segment's underwriting income are discussed below.

        Premiums Written.    Gross premiums written by the reinsurance segment were $1.7 billion in 2006, compared to $1.75 billion for 2005. Gross premiums written for 2006 reflects a lower level of international casualty business in response to actual and anticipated market conditions, partially offset by growth in international property and marine lines, due to higher rates and an increase in exposure. Catastrophe-exposed property and marine lines have continued to provide attractive opportunities in the wake of the 2005 storms. As a result of the significant catastrophic activity in 2005 and the impact of such events on the insurance market, the reinsurance segment was able to write certain property (both catastrophe and non-catastrophe) and marine business in the 2005 fourth quarter, which resulted in approximately $109.2 million of gross premiums written ($100.2 million on a net basis). Such business did not contribute to the reinsurance segment's 2006 premiums written.

        Ceded premiums written by the reinsurance segment were 19.9% of gross premiums written for 2006, compared to 5.3% for 2005. The higher ceded percentage in 2006 primarily resulted from the $273.2 million of premiums written ceded by Arch Re Bermuda to Flatiron Re Ltd. ($157.4 million on an earned basis) under a quota-share reinsurance treaty, as previously disclosed.

        Net premiums written by the reinsurance segment were $1.37 billion for 2006, compared to $1.66 billion for 2005. Net premiums written for 2006 reflects the lower level of international casualty business noted above, which more than offset growth in international property and marine lines, net of the amounts ceded to Flatiron Re Ltd. In addition, net premiums written in 2005 included $100.2 million of non-recurring business, as noted above. For information regarding net premiums written by major line and type of business and geographic location, refer to note 3, "Segment Information," of the notes accompanying our consolidated financial statements.

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        Net Premiums Earned.    Net premiums earned for our reinsurance segment were $1.48 billion for 2006, compared to $1.59 billion for 2005, and generally reflect changes in net premiums written over the previous five quarters, including the mix and type of business written.

        Fee Income.    The reinsurance segment recorded $4.7 million of fee income for 2006, compared to $5.0 million for 2005. The 2006 amount related to certain assumed reinsurance contracts which were deemed, under GAAP, not to transfer insurance risk, and are accounted for using the deposit method of accounting. Of the 2005 amount, $4.5 million related to an industry loss warranty contract. Under this contract, we received payment when industry-wide losses from certain natural perils exceeded a specified amount.

        Losses and Loss Adjustment Expenses.    Reinsurance segment losses and loss adjustment expenses incurred for 2006 were $773.3 million, or 52.2% of net premiums earned, compared to $1.05 billion, or 66.3% of net premiums earned, for 2005. The reinsurance segment's 2006 results included approximately $45.9 million, or 3.1 points, related to 2006 catastrophe losses, while the 2005 results included $208.5 million, or 13.1 points, related to Hurricanes Dennis, Emily, Katrina, Rita and Wilma and the European Floods and $24.0 million, or 1.5 points, of other catastrophe losses. In addition, the 2006 loss ratio reflected a 4.6 point reduction related to estimated net favorable development in prior year loss reserves, compared to a 5.8 point reduction in 2005.

        In its reserving process in 2002 and 2003, the reinsurance segment recognized that there is a possibility that the assumptions made could prove to be inaccurate due to several factors primarily related to the start up nature of its operations. Due to the availability of additional data, and based on reserve analyses, it was determined that it was no longer necessary to continue to include such factors in the reserving process in 2004. Following reserve reviews, and based on the level of claims activity reported to date, the reinsurance segment has reduced the amount it had recorded in 2002 and 2003 by $7.7 million in 2006 and $12.1 million in 2005. Such amounts are reflected in the prior year development shown above.

        The net favorable development on prior year loss reserves in both periods was partially offset by increased acquisition expenses, primarily as a result of the commutation of certain treaties. Such activity resulted in an increase to the acquisition expense ratio of approximately 0.5 points in 2006, compared to 0.6 points in 2005. The remainder of the change in the loss ratio for 2006, compared to 2005, resulted from better results recorded in the reinsurance segment's property lines of business and changes in their mix of business.

        For a discussion of the reserves for losses and loss adjustment expenses, please refer to the section above entitled "Critical Accounting Policies, Estimates and Recent Accounting Pronouncements—Reserves for Losses and Loss Adjustment Expenses."

        Underwriting Expenses.    The underwriting expense ratio for the reinsurance segment was 28.5% for 2006, compared to 31.2% for 2005. The acquisition expense ratio for 2006 was 24.9%, compared to 27.9% for 2005. The reinsurance segment's 2006 results included commission income (in excess of the reimbursement of direct acquisition expenses) on the quota-share reinsurance treaty with Flatiron Re Ltd., which reduced the acquisition expense ratio by 1.6 points in 2006. The 2005 results included $13.3 million of assessments incurred as a result of the 2005 hurricane activity, which added 0.8 points to the 2005 acquisition expense ratio. The reinsurance segment's other operating expense ratio was 3.6% for 2006, compared to 3.3% for 2005.

        Net investment income was $380.2 million for 2006, compared to $232.9 million for 2005. The increase in net investment income in 2006 resulted from a higher level of average invested assets primarily generated by cash flows from operations. In addition, an increase in the pre-tax investment

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income yield to 4.71% for 2006 from 3.68% for 2005 contributed to the growth in net investment income. These yields were calculated based on amortized cost. Yields on future investment income may vary based on financial market conditions, investment allocation decisions and other factors.

        Following is a summary of net realized gains (losses):

 
   Years Ended
December 31,
  
(U.S. dollars in thousands)
   2006
   2005
  
Fixed maturities   ($ 27,379 ) ($ 56,770 )
Other investments     4,186     1,016  
Other     3,756     2,298  
   
 
 
Total   ($ 19,437 ) ($ 53,456 )
   
 
 

        Total return on our portfolio under management for 2006 was 5.24%, compared to 2.09% for 2005. Total return is calculated on a pre-tax basis and before investment expenses. The higher total return in 2006 compared to 2005 was primarily due to movements in interest rates during the periods. The increase in interest rates in 2005 was greater than the increase in 2006 and resulted in a lower relative return compared to 2006. For 2006, net realized losses on our fixed maturities of $27.4 million included a provision of $31.6 million for declines in the fair value of investments held in our available for sale portfolio which were considered to be other-than-temporary, based on a review performed during 2006. For 2005, net realized losses on our fixed maturities of $56.8 million included a provision of $25.7 million for declines in the fair value of investments held in our available for sale portfolio which were considered to be other-than-temporary, based on a review performed during 2005. In periods subsequent to the recognition of an other-than-temporary impairment on fixed maturities, we account for such securities as if they had been purchased on the measurement date of the other-than temporary impairment and the provision for the other-than-temporary impairment (reflected as a discount or reduced premium based on the new cost basis) is amortized into net investment income over the remaining life of the fixed maturities, or until such securities are sold. The declines in fair value on such securities were primarily due to the current interest rate environment. The balance of $4.2 million in net realized gains on our fixed maturities in 2006 resulted from the sale of securities, compared to net realized losses from the sale of fixed maturities of $31.1 million for 2005. For the 2006 and 2005 periods, net realized gains or losses from the sale of fixed maturities resulted from our decisions to reduce credit exposure, changes in duration targets, relative value determinations and sales related to rebalancing the portfolio.

        Other expenses, which are included in our other operating expenses and part of our corporate and other segment (non-underwriting), were $29.1 million for 2006, compared to $25.8 million for 2005. Such amounts primarily represent certain holding company costs necessary to support our worldwide insurance and reinsurance operations, share based compensation expense and costs associated with operating as a publicly traded company. Other expenses for 2005 included approximately $1.9 million of costs related to an agreement entered into with Robert Clements, former Chairman of our board of directors, and approximately $4.9 million of costs related to an agreement entered into with Dwight Evans, former Chairman and Chief Executive Officer of Arch Worldwide Reinsurance Group. See note 10, "Transactions with Related Parties," of the notes accompanying our consolidated financial statements.

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        As required by the provisions of SFAS 123(R), we recorded pre-tax share-based compensation expense related to stock options of $9.2 million in 2006. Under the modified prospective method of transition, no expense related to stock options was recorded in 2005. Therefore, results for 2006 are not comparable to 2005. See note 13, "Share Capital," of the notes accompanying our consolidated financial statements and "Critical Accounting Policies, Estimates and Recent Accounting Policies—Share-Based Compensation" for more information about the adoption of SFAS No. 123(R).

        Interest expense was $22.1 million for 2006, compared to $22.5 million for 2005. Such amounts primarily relate to the $300 million in 7.35% senior notes outstanding in both periods.

        Net foreign exchange losses for 2006 of $23.9 million consisted of net unrealized losses of $27.3 million and net realized gains of $3.4 million, compared to net foreign exchange gains of $22.2 million for 2005, which consisted of net unrealized gains of $23.3 million and net realized losses of $1.1 million. For the 2006 and 2005 periods, the net unrealized foreign exchange gains or losses recorded were largely offset by changes in the value of our investments held in foreign currencies.

        The income tax provision on income before income taxes resulted in an effective tax rate of 3.6% for 2006, compared to 10.1% for 2005. Our effective tax rate fluctuates from year to year consistent with the relative mix of income reported by jurisdiction due primarily to the varying tax rates in each jurisdiction. A significant portion of our catastrophe-exposed property business is written by a Bermuda-based subsidiary. As a result, on a relative basis, our effective tax rate is likely to be favorably affected in periods that have a low level of catastrophic losses incurred and adversely impacted in periods with significant catastrophic claims activity.

Liquidity and Capital Resources

        ACGL is a holding company whose assets primarily consist of the shares in its subsidiaries. Generally, ACGL depends on its available cash resources, liquid investments and dividends or other distributions from its subsidiaries to make payments, including the payment of debt service obligations and operating expenses it may incur and any dividends or liquidation amounts with respect to the series A non-cumulative and series B non-cumulative preferred shares and common shares.

        On a consolidated basis, our aggregate cash and invested assets totaled $10.13 billion at December 31, 2007, compared to $9.32 billion at December 31, 2006. ACGL's readily available cash, short-term investments and marketable securities, excluding amounts held by our regulated insurance and reinsurance subsidiaries, totaled $36.3 million at December 31, 2007, compared to $14.2 million at December 31, 2006. For 2007, 2006 and 2005, ACGL received dividends of $602.1 million, $22.1 million and $22.1 million from Arch Re Bermuda which were used to fund the share repurchase program described below along with the payment of preferred dividends, interest expense and other corporate expenses.

        The ability of our regulated insurance and reinsurance subsidiaries to pay dividends or make distributions or other payments to us is dependent on their ability to meet applicable regulatory standards. Under Bermuda law, Arch Re Bermuda is required to maintain a minimum solvency margin (i.e., the amount by which the value of its general business assets must exceed its general business liabilities) equal to the greatest of (1) $100 million, (2) 50% of net premiums written (being gross premiums written by us less any premiums ceded by us, but we may not deduct more than 25% of gross premiums when computing net premiums written) and (3) 15% of loss and other insurance

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reserves. Arch Re Bermuda is prohibited from declaring or paying any dividends during any financial year if it is not in compliance with its minimum solvency margin or minimum liquidity ratio. In addition, Arch Re Bermuda is prohibited from declaring or paying in any financial year dividends of more than 25% of its total statutory capital and surplus (as shown on its previous financial year's statutory balance sheet) unless it files, at least seven days before payment of such dividends, with the Bermuda Monetary Authority an affidavit stating that it will continue to meet the required margins. In addition, Arch Re Bermuda is prohibited, without prior approval of the Bermuda Monetary Authority, from reducing by 15% or more its total statutory capital, as set out in its previous year's statutory financial statements. At December 31, 2007, as determined under Bermuda law, Arch Re Bermuda had statutory capital of $2.0 billion and statutory capital and surplus of $3.73 billion. Such amounts include ownership interests in U.S. insurance and reinsurance subsidiaries. Accordingly, Arch Re Bermuda can pay approximately $933 million to ACGL during 2008 without providing an affidavit to the Bermuda Monetary Authority, as discussed above. Our U.S. insurance and reinsurance subsidiaries can pay approximately $113.9 million in dividends or distributions to Arch-U.S., our U.S. holding company, which is owned by Arch Re Bermuda, during 2008 without prior regulatory approval. Such dividends or distributions may be subject to applicable withholding or other taxes. Arch-Europe can pay approximately £8.4 million, or $16.7 million, in dividends to ACGL during 2008 without prior notice and approval by the FSA. In addition, the ability of our insurance and reinsurance subsidiaries to pay dividends is also constrained by our dependence on the financial strength ratings of our insurance and reinsurance subsidiaries from independent rating agencies. The ratings from these agencies depend to a large extent on the capitalization levels of our insurance and reinsurance subsidiaries. We believe that ACGL has sufficient cash resources and available dividend capacity to service its indebtedness and other current outstanding obligations.

        Our insurance and reinsurance subsidiaries are required to maintain assets on deposit, which primarily consist of fixed maturities, with various regulatory authorities to support their operations. The assets on deposit are available to settle insurance and reinsurance liabilities to third parties. Our insurance and reinsurance subsidiaries also have investments in segregated portfolios primarily to provide collateral or guarantees for letters of credit to third parties. At December 31, 2007 and 2006, such amounts approximated $1.17 billion and $1.16 billion, respectively. In addition, certain of our operating subsidiaries maintain assets in trust accounts as collateral for insurance and reinsurance transactions with affiliated companies. At December 31, 2007 and 2006, such amounts approximated $3.8 billion and $3.61 billion, respectively.

        ACGL, through its subsidiaries, provides financial support to certain of its insurance subsidiaries and affiliates, through certain reinsurance arrangements essential to the ratings of such subsidiaries. Except as described in the preceding sentence, or where express reinsurance, guarantee or other financial support contractual arrangements are in place, each of ACGL's subsidiaries or affiliates is solely responsible for its own liabilities and commitments (and no other ACGL subsidiary or affiliate is so responsible). Any reinsurance arrangements, guarantees or other financial support contractual arrangements that are in place are solely for the benefit of the ACGL subsidiary or affiliate involved and third parties (creditors or insureds of such entity) are not express beneficiaries of such arrangements.

        Our insurance and reinsurance operations provide liquidity in that premiums are received in advance, sometimes substantially in advance, of the time losses are paid. The period of time from the occurrence of a claim through the settlement of the liability may extend many years into the future. Sources of liquidity include cash flows from operations, financing arrangements or routine sales of investments.

        As part of our investment strategy, we seek to establish a level of cash and highly liquid short-term and intermediate-term securities which, combined with expected cash flow, is believed by us to be adequate to meet our foreseeable payment obligations. However, due to the nature of our operations,

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cash flows are affected by claim payments that may comprise large payments on a limited number of claims and which can fluctuate from year to year. We believe that our liquid investments and cash flow will provide us with sufficient liquidity in order to meet our claim payment obligations. However, the timing and amounts of actual claim payments related to recorded Loss Reserves vary based on many factors, including large individual losses, changes in the legal environment, as well as general market conditions. The ultimate amount of the claim payments could differ materially from our estimated amounts. Certain lines of business written by us, such as excess casualty, have loss experience characterized as low frequency and high severity. The foregoing may result in significant variability in loss payment patterns. The impact of this variability can be exacerbated by the fact that the timing of the receipt of reinsurance recoverables owed to us may be slower than anticipated by us. Therefore, the irregular timing of claim payments can create significant variations in cash flows from operations between periods and may require us to utilize other sources of liquidity to make these payments, which may include the sale of investments or utilization of existing or new credit facilities or capital market transactions. If the source of liquidity is the sale of investments, we may be forced to sell such investments at a loss, which may be material.

        Consolidated cash provided by operating activities was $1.44 billion for 2007, compared to $1.61 billion for 2006. The lower level of operating cash flows for 2007 primarily resulted from an increase in paid losses as our insurance and reinsurance loss reserves continue to mature, along with a lower level of premiums written and collected. Cash flow from operating activities are provided by premiums collected, fee income, investment income and collected reinsurance recoverables, offset by losses and loss adjustment expense payments, reinsurance premiums paid, operating costs and current taxes paid.

        We expect that our operational needs, including our anticipated insurance obligations and operating and capital expenditure needs, for the next twelve months, at a minimum, will be met by our balance of cash, short-term investments and our credit facilities, as well as by funds generated from underwriting activities and investment income and proceeds on the sale or maturity of our investments. See "—Contractual Obligations and Commercial Commitments—Contractual Obligations" for an analysis of our contractual commitments at December 31, 2007.

        We monitor our capital adequacy on a regular basis and will seek to adjust our capital base (up or down) according to the needs of our business. The future capital requirements of our business will depend on many factors, including our ability to write new business successfully and to establish premium rates and reserves at levels sufficient to cover losses. Our ability to underwrite is largely dependent upon the quality of our claims paying and financial strength ratings as evaluated by independent rating agencies. In particular, we require (1) sufficient capital to maintain our financial strength ratings, as issued by several ratings agencies, at a level considered necessary by management to enable our key operating subsidiaries to compete; (2) sufficient capital to enable our underwriting subsidiaries to meet the capital adequacy tests performed by statutory agencies in the U.S. and other key markets; and (3) letters of credit and other forms of collateral that are necessary for our non-U.S. operating companies because they are "non-admitted" under U.S. state insurance regulations.

        As part of our capital management program, we may seek to raise additional capital or may seek to return capital to our shareholders through share repurchases, cash dividends or other methods (or a combination of such methods). Any such determination will be at the discretion of our board of directors and will be dependent upon our profits, financial requirements and other factors, including legal restrictions, rating agency requirements and such other factors as our board of directors deems relevant.

        On February 28, 2007, our Board of Directors authorized us to invest up to $1 billion in ACGL's common shares through a share repurchase program. Repurchases under the program may be effected from time to time in open market or privately negotiated transactions through February 2009. In 2007,

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we repurchased approximately 7.8 million common shares for an aggregate purchase price of $537.1 million. As a result of share repurchase transactions, book value per common share at December 31, 2007 was reduced by $1.45 per share and weighted average shares outstanding were reduced by 3.3 million. In 2008 (through February 25), approximately 2.1 million common shares were repurchased for an aggregate purchase price of $144.8 million. The timing and amount of the repurchase transactions under this program will depend on a variety of factors, including market conditions and corporate and regulatory considerations. In connection with the repurchase program, the Warburg Pincus funds and the Hellman & Friedman funds waived their rights relating to share repurchases under the shareholders agreement for all repurchases of common shares by ACGL under the repurchase program in open market transactions and certain privately negotiated transactions. In May 2007, the Hellman & Friedman funds ceased to own shares of ACGL and their rights under the shareholders agreement with ACGL terminated. See "Market for Registrant's Common Equity, Related Stockholder Matters and Issuer Purchases of Equity Securities—Issuer Purchases of Equity Securities."

        To the extent that our existing capital is insufficient to fund our future operating requirements or maintain such ratings, we may need to raise additional funds through financings or limit our growth. If we are not able to obtain adequate capital, our business, results of operations and financial condition could be adversely affected, which could include, among other things, the following possible outcomes: (1) potential downgrades in the financial strength ratings assigned by ratings agencies to our operating subsidiaries, which could place those operating subsidiaries at a competitive disadvantage compared to higher-rated competitors; (2) reductions in the amount of business that our operating subsidiaries are able to write in order to meet capital adequacy-based tests enforced by statutory agencies; and (3) any resultant ratings downgrades could, among other things, affect our ability to write business and increase the cost of bank credit and letters of credit.

        In addition to common share capital, we depend on external sources of finance to support our underwriting activities, which can be in the form (or any combination) of debt securities, preference shares, common equity and bank credit facilities providing loans and/or letters of credit. Any equity or debt financing, if available at all, may be on terms that are unfavorable to us. In the case of equity financings, dilution to our shareholders could result, and, in any case, such securities may have rights, preferences and privileges that are senior to those of our outstanding securities.

        In June 2006, ACGL and Arch-U.S. filed a universal shelf registration statement with the SEC. This registration statement allows for the possible future offer and sale by us of various types of securities, including unsecured debt securities, preference shares, common shares, warrants, share purchase contracts and units and depositary shares. The shelf registration statement enables us to efficiently access the public debt and/or equity capital markets in order to meet our future capital needs. The shelf registration statement also allows selling shareholders to resell common shares that they own in one or more offerings from time to time. We will not receive any proceeds from any shares offered by the selling shareholders. This report is not an offer to sell or the solicitation of an offer to buy nor shall there be any sale of these securities in any state in which such offer, solicitation or sale would be unlawful prior to registration or qualification under the securities laws of any such state.

        In August 2006, we entered into a five-year agreement for a $300 million unsecured revolving loan and letter of credit facility and a $1.0 billion secured letter of credit facility. The $300 million unsecured loan and letter of credit facility is also available for the issuance of unsecured letters of credit up to $100 million for our U.S.-based reinsurance operation.

        During 2006, ACGL completed two public offerings of non-cumulative preferred shares. On February 1, 2006, $200.0 million principal amount of 8.0% series A non-cumulative preferred shares ("series A preferred shares") were issued with net proceeds of $193.5 million and, on May 24, 2006, $125.0 million principal amount of 7.875% series B non-cumulative preferred shares ("series B preferred shares" and together with the series A preferred shares, the "preferred shares") were issued

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with net proceeds of $120.9 million. The net proceeds of the offerings were used to support the underwriting activities of ACGL's insurance and reinsurance subsidiaries. ACGL has the right to redeem all or a portion of each series of preferred shares at a redemption price of $25.00 per share on or after (1) February 1, 2011 for the series A preferred shares and (2) May 15, 2011 for the series B preferred shares. Dividends on the preferred shares are non-cumulative. Consequently, in the event dividends are not declared on the preferred shares for any dividend period, holders of preferred shares will not be entitled to receive a dividend for such period, and such undeclared dividend will not accrue and will not be payable. Holders of preferred shares will be entitled to receive dividend payments only when, as and if declared by ACGL's board of directors or a duly authorized committee of the board of directors. Any such dividends will be payable from the date of original issue on a non-cumulative basis, quarterly in arrears. To the extent declared, these dividends will accumulate, with respect to each dividend period, in an amount per share equal to 8.0% of the $25.00 liquidation preference per annum for the series A preferred shares and 7.875% of the $25.00 liquidation preference per annum for the series B preferred shares. For 2007 and 2006, we paid $25.8 million and $17.4 million, respectively, to holders of the preferred shares and, at December 31, 2007, had declared an aggregate of $3.3 million of dividends to be paid to holders of the preferred shares.

        At December 31, 2007, ACGL's capital of $4.34 billion consisted of $300.0 million of senior notes, representing 6.9% of the total, $325.0 million of preferred shares, representing 7.5% of the total, and common shareholders' equity of $3.71 billion, representing the balance. At December 31, 2006, ACGL's capital of $3.89 billion consisted of $300.0 million of senior notes, representing 7.7% of the total, $325.0 million of preferred shares, representing 8.4% of the total, and common shareholders' equity of $3.27 billion, representing the balance. The increase in capital during 2007 of $445.2 million was primarily attributable to net income for 2007 and an after-tax increase in the fair value of our investment portfolio, partially offset by $537.1 million of share repurchases during the period. The increase in the fair value of our investment portfolio primarily resulted from changes in the level of interest rates in the second half of 2007.

Natural and Man-Made Catastrophic Events

        We have large aggregate exposures to natural and man-made catastrophic events. Catastrophes can be caused by various events, including, but not limited to, hurricanes, floods, windstorms, earthquakes, hailstorms, explosions, severe winter weather and fires. Catastrophes can also cause losses in non-property business such as workers' compensation or general liability. In addition to the nature of property business, we believe that economic and geographic trends affecting insured property, including inflation, property value appreciation and geographic concentration, tend to generally increase the size of losses from catastrophic events over time.

        We have substantial exposure to unexpected, large losses resulting from future man-made catastrophic events, such as acts of war, acts of terrorism and political instability. These risks are inherently unpredictable and recent events may lead to increased frequency and severity of losses. It is difficult to predict the timing of such events with statistical certainty or estimate the amount of loss any given occurrence will generate. It is not possible to completely eliminate our exposure to unforecasted or unpredictable events and, to the extent that losses from such risks occur, our financial condition and results of operations could be materially adversely affected. Therefore, claims for natural and man-made catastrophic events could expose us to large losses and cause substantial volatility in our results of operations, which could cause the value of our common shares to fluctuate widely. In certain instances, we specifically insure and reinsure risks resulting from terrorism. Even in cases where we attempt to exclude losses from terrorism and certain other similar risks from some coverages written by us, we may not be successful in doing so. Moreover, irrespective of the clarity and inclusiveness of policy language, there can be no assurance that a court or arbitration panel will limit enforceability of policy language or otherwise issue a ruling adverse to us.

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        We seek to limit our loss exposure by writing a number of our reinsurance contracts on an excess of loss basis, adhering to maximum limitations on reinsurance written in defined geographical zones, limiting program size for each client and prudent underwriting of each program written. In the case of proportional treaties, we may seek per occurrence limitations or loss ratio caps to limit the impact of losses from any one or series of events. In our insurance operations, we seek to limit our exposure through the purchase of reinsurance. We cannot be certain that any of these loss limitation methods will be effective. We also seek to limit our loss exposure by geographic diversification. Geographic zone limitations involve significant underwriting judgments, including the determination of the area of the zones and the inclusion of a particular policy within a particular zone's limits. There can be no assurance that various provisions of our policies, such as limitations or exclusions from coverage or choice of forum, will be enforceable in the manner we intend. Disputes relating to coverage and choice of legal forum may also arise. Underwriting is inherently a matter of judgment, involving important assumptions about matters that are inherently unpredictable and beyond our control, and for which historical experience and probability analysis may not provide sufficient guidance. One or more catastrophic or other events could result in claims that substantially exceed our expectations, which could have a material adverse effect on our financial condition or our results of operations, possibly to the extent of eliminating our shareholders' equity.

        For our natural catastrophe exposed business, we seek to limit the amount of exposure we will assume from any one insured or reinsured and the amount of the exposure to catastrophe losses from a single event in any geographic zone. We monitor our exposure to catastrophic events, including earthquake and wind and periodically reevaluate the estimated probable maximum pre-tax loss for such exposures. Our estimated probable maximum pre-tax loss is determined through the use of modeling techniques, but such estimate does not represent our total potential loss for such exposures. We seek to limit the probable maximum pre-tax loss to a specific level for severe catastrophic events. Currently, we generally seek to limit the probable maximum pre-tax loss to approximately 25% of total shareholders' equity for a severe catastrophic event in any geographic zone that could be expected to occur once in every 250 years, although we reserve the right to change this threshold at any time. There can be no assurances that we will not suffer pre-tax losses greater than 25% of our total shareholders' equity from one or more catastrophic events due to several factors, including the inherent uncertainties in estimating the frequency and severity of such events and the margin of error in making such determinations resulting from potential inaccuracies and inadequacies in the data provided by clients and brokers, the modeling techniques and the application of such techniques or as a result of a decision to change the percentage of shareholders' equity exposed to a single catastrophic event. In addition, depending on business opportunities and the mix of business that may comprise our insurance and reinsurance portfolio, we may seek to adjust our self-imposed limitations on probable maximum pre-tax loss for catastrophe exposed business. See "—Critical Accounting Policies, Estimates and Recent Accounting Pronouncements—Ceded Reinsurance" for a discussion of our catastrophe reinsurance programs.

Contractual Obligations and Commercial Commitments

        As of December 31, 2007, we had access to a $300 million unsecured revolving loan and letter of credit facility and a $1.0 billion secured letter of credit facility (the "Credit Agreement"). The $300 million unsecured revolving loan is also available for the issuance of unsecured letters of credit up to $100 million for Arch Re U.S. Borrowings of revolving loans may be made by ACGL and Arch Re U.S. at a variable rate based on LIBOR or an alternative base rate at our option. Secured letters of credit are available for issuance on behalf of our insurance and reinsurance subsidiaries. Issuance of letters of credit and borrowings under the Credit Agreement are subject to our compliance with certain covenants and conditions, including absence of a material adverse change. These covenants require,

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among other things, that we maintain a debt to shareholders' equity ratio of not greater than 0.35 to 1 and shareholders' equity in excess of $1.95 billion plus 25% of future aggregate net income for each quarterly period (not including any future net losses) beginning after June 30, 2006 and 25% of future aggregate proceeds from the issuance of common or preferred equity and that our principal insurance and reinsurance subsidiaries maintain at least a "B++" rating from A.M. Best. In addition, certain of our subsidiaries which are party to the Credit Agreement are required to maintain minimum shareholders' equity levels. We were in compliance with all covenants contained in the Credit Agreement at December 31, 2007. The Credit Agreement expires on August 30, 2011.

        Issuance of letters of credit and borrowings under the Credit Agreement are subject to our compliance with certain covenants and conditions, including absence of a material adverse change. These covenants require, among other things, that we maintain a debt to shareholders' equity ratio of not greater than 0.35 to 1 and shareholders' equity in excess of $1.95 billion plus 25% of future aggregate net income for each quarterly period (not including any future net losses) beginning after June 30, 2006 and 25% of future aggregate proceeds from the issuance of common or preferred equity and that our principal insurance and reinsurance subsidiaries maintain at least a "B++" rating from A.M. Best. In addition, certain of our subsidiaries which are party to the Credit Agreement are required to maintain minimum shareholders' equity levels.

        Including the secured letter of credit portion of the Credit Agreement and another letter of credit facility (together, the "LOC Facilities"), we have access to letter of credit facilities for up to a total of $1.45 billion. The principal purpose of the LOC Facilities is to issue, as required, evergreen standby letters of credit in favor of primary insurance or reinsurance counterparties with which we have entered into reinsurance arrangements to ensure that such counterparties are permitted to take credit for reinsurance obtained from our reinsurance subsidiaries in United States jurisdictions where such subsidiaries are not licensed or otherwise admitted as an insurer, as required under insurance regulations in the United States, and to comply with requirements of Lloyd's of London in connection with qualifying quota share and other arrangements. The amount of letters of credit issued is driven by, among other things, the timing and payment of catastrophe losses, loss development of existing reserves, the payment pattern of such reserves, the further expansion of our business and the loss experience of such business. When issued, certain letters of credit are secured by a portion of our investment portfolio. In addition, the LOC Facilities also require the maintenance of certain covenants, which we were in compliance with at December 31, 2007. At such date, we had approximately $612.4 million in outstanding letters of credit under the LOC Facilities, which were secured by investments totaling $652.8 million. The other letter of credit facility was replaced on substantially the same terms in December 2007. It is anticipated that the LOC Facilities will be renewed (or replaced) on expiry, but such renewal (or replacement) will be subject to the availability of credit from banks which we utilize. In addition to letters of credit, we have established and may establish additional insurance trust accounts in the U.S. and Canada to secure our reinsurance amounts payable as required. See note 7, "Investment Information," of the notes accompanying our consolidated financial statements.

        On May 4, 2004, ACGL completed a public offering of $300 million principal amount of 7.35% senior notes ("Senior Notes") due May 1, 2034 and received net proceeds of $296.4 million. ACGL used $200 million of the net proceeds to repay all amounts outstanding under a revolving credit agreement. The Senior Notes are ACGL's senior unsecured obligations and rank equally with all of its existing and future senior unsecured indebtedness. Interest payments on the Senior Notes are due on May 1st and November 1st of each year. ACGL may redeem the Senior Notes at any time and from time to time, in whole or in part, at a "make-whole" redemption price. For 2007, 2006 and 2005, interest expense on the Senior Notes was approximately $22.1 million. The market value of the Senior Notes at December 31, 2007 and 2006 was $325.4 million and $332.0 million, respectively.

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        The following table provides an analysis of our contractual commitments at December 31, 2007:

 
    
   Payment due by period
(U.S. dollars in thousands)

   Total
   Less than 1 year
   1 - 3
years
   4 - 5
years
   More than
5 years
Long-term debt obligations   $ 300,000     —     —     —   $ 300,000
Interest expense on long-term debt obligations     584,325     22,050     44,100     44,100     474,075
Operating lease obligations     91,204     14,346     31,614     26,568     18,676
Purchase obligations     22,013     10,119     11,894     —     —
Reserves for losses and loss adjustment expenses, gross(1)     7,092,452     2,073,060     2,383,358     1,091,084     1,544,950
Deposit accounting liabilities(2)     43,506     2,523     6,141     8,850     25,992
Securities lending collateral(3)     1,503,723     1,503,723     —     —     —
Unfunded investment commitments     150,180     150,180     —     —     —
   
 
 
 
 
Total   $ 9,787,403   $ 3,776,001   $ 2,477,107   $ 1,170,602   $ 2,363,693
   
 
 
 
 
(1)
The estimated expected contractual commitments related to the reserves for losses and loss adjustment expenses are presented on a gross basis. It should be noted that until a claim has been presented to us, determined to be valid, quantified and settled, there is no known obligation on an individual transaction basis, and while estimable in the aggregate, the timing and amount contain significant uncertainty. Approximately 72.4% of our net reserves were incurred but not reported at December 31, 2007.

(2)
The estimated expected contractual commitments related to deposit accounting liabilities have been estimated using projected cash flows from the underlying contracts. It should be noted that, due to the nature of such liabilities, the timing and amount contain significant uncertainty.

(3)
As part of our securities lending program, we loan certain fixed income securities to third parties and receive collateral, primarily in the form of cash. The collateral received is reinvested and is reflected as "short-term investment of funds received under securities lending agreements, at fair value." Such collateral is due back to the third parties at the close of the securities lending transaction.

Off-Balance Sheet Arrangements

        We are not party to any transaction, agreement or other contractual arrangement to which an entity unconsolidated with us is a party that management believes is reasonably likely to have a current or future effect on our financial condition, revenues or expenses, results of operations, liquidity, capital expenditures or capital resources that is material to investors. We concluded that, under FASB Interpretation No. 46R, "Consolidation of Variable Interest Entities," which was issued and became effective for us during the 2004 first quarter, we are required to consolidate the assets, liabilities and results of operations (if any) of a certain managing general agency in which one of our subsidiaries has an investment. Such agency ceased producing business in 1999 and is currently running-off its operations. Based on current information, there are no assets or liabilities of such agency required to be reflected on the face of our consolidated financial statements that are not, or have not been previously, otherwise reflected therein.

        On December 29, 2005, Arch Re Bermuda entered into a quota share reinsurance treaty with Flatiron Re Ltd. pursuant to which Flatiron Re Ltd. assumed a 45% quota share (the "Flatiron Treaty") of certain lines of property and marine business underwritten by Arch Re Bermuda for unaffiliated third parties for the 2006 and 2007 underwriting years (January 1, 2006 to December 31, 2007). Effective June 28, 2006, the parties amended the Flatiron Treaty to increase the percentage ceded to Flatiron Re Ltd. from 45% to 70% of all covered business bound by Arch Re Bermuda from (and including) June 28, 2006 until (and including) August 15, 2006 provided such business did not

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incept beyond September 30, 2006. The ceding percentage for all business bound outside of this period continued to be 45%. On December 31, 2007, the Flatiron Treaty expired by its terms. As a result of the terms of the Flatiron Treaty, we determined that Flatiron Re Ltd. is a variable interest entity. However, Arch Re Bermuda is not the primary beneficiary of Flatiron Re Ltd. and, as such, we are not required to consolidate the assets, liabilities and results of operations of Flatiron Re Ltd. per FIN 46R. See note 11, "Commitments and Contingencies," of the notes accompanying our consolidated financial statements for further details on the Flatiron Treaty.

Investments

        The finance and investment committee of our board of directors establishes our investment policies and creates guidelines for our investment managers. The finance and investment committee reviews the implementation of the investment strategy on a regular basis. Our current approach stresses preservation of capital, market liquidity and diversification of risk.

        Our cash and invested assets were as follows at December 31, 2007 and 2006:

 
   December 31,
(U.S. dollars in thousands)

   2007
   2006
Fixed maturities available for sale, at fair value   $ 7,137,998   $ 6,876,548
Fixed maturities pledged under securities lending agreements, at fair value(1)     1,462,826     860,803
   
 
  Total fixed maturities     8,600,824     7,737,351
Short-term investments available for sale, at fair value     699,036     957,698
Short-term investments pledged under securities lending agreements, at fair value(1)     219     —
Cash     239,915     317,017
Other investments, at fair value     589,669     307,082
   
 
  Total cash and invested assets(1)(2)   $ 10,129,663   $ 9,319,148
   
 
(1)
In our securities lending transactions, we receive collateral in excess of the fair value of the fixed maturities and short-term investments pledged under securities lending agreements. For purposes of this table, we have excluded $1.5 billion and $891.4 million, respectively, of collateral received which is reflected as "short-term investment of funds received under securities lending agreements, at fair value" and included $1.46 billion and $860.8 million, respectively, of "fixed maturities and short-term investments pledged under securities lending agreements, at fair value" at December 31, 2007 and 2006.

(2)
Includes certain securities transactions entered into but not settled at the balance sheet date. Net of such amounts, total cash and investments were approximately $10.1 billion at December 31, 2007 and $9.09 billion at December 31, 2006.

        At December 31, 2007, our fixed income portfolio, which includes fixed maturity securities and short-term investments, had a "AA+" average credit quality rating, an average effective duration of 3.29 years, and an average yield to maturity (imbedded book yield), before investment expenses, of 5.03%. At December 31, 2006, our fixed income portfolio, which includes fixed maturity securities and short-term investments, had a "AAA" average credit quality rating, an average effective duration of 3.23 years, and an average yield to maturity (imbedded book yield), before investment expenses, of 4.97%.

        Our portfolio includes investments, such as mortgage-backed securities, which are subject to prepayment risk. At December 31, 2007, our investments in mortgage-backed securities, excluding commercial mortgage-backed securities, amounted to approximately $1.23 billion, or 12.2% of total investments and cash, compared to $1.18 billion, or 12.7%, at December 31, 2006. Such amounts are classified as "available for sale" and are not held for trading purposes. In addition, our fixed maturities at December 31, 2007 include exposures to certain corporate sectors, such as the financial sector (11% of total investments and cash) and the industrial sector (7% of total investments and cash).

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        In recent months, delinquencies and losses with respect to residential mortgage loans generally have increased and may continue to increase, particularly in the subprime sector. In addition, in recent months residential property values in many states have declined or remained stable, after extended periods during which those values appreciated. A continued decline or an extended flattening in those values may result in additional increases in delinquencies and losses on residential mortgage loans generally, especially with respect to second homes and investment properties, and with respect to any residential mortgage loans where the aggregate loan amounts (including any subordinate loans) are close to or greater than the related property values. These developments may have a significant adverse effect on the prices of loans and securities, including those in our investment portfolio. The situation continues to have wide ranging consequences, including downward pressure on economic growth and the potential for increased insurance and reinsurance exposures, which could have an adverse impact on our results of operations, financial condition, business and operations.

        Our Chief Investment Officer administers the investment portfolio, oversees our investment managers, formulates investment strategy in conjunction with our finance and investment committee and directly manages certain portions of our fixed income portfolio. At December 31, 2007, approximately $4.61 billion, or 45.5%, of our total investments and cash was internally managed, compared to $3.9 billion, or 41.8%, at December 31, 2006. While maintaining our emphasis on preservation of capital and liquidity, we expect our portfolio to become more diversified and, as a result, we may expand into areas which are not currently part of our investment strategy.

        We participate in a securities lending program under which certain of our fixed income portfolio securities are loaned to third parties, primarily major brokerage firms, for short periods of time through a lending agent. Such securities have been reclassified as "Fixed maturities and short-term investments pledged under securities lending agreements, at fair value." We maintain control over the securities we lend, retain the earnings and cash flows associated with the loaned securities and receive a fee from the borrower for the temporary use of the securities. Collateral received, primarily in the form of cash, is required at a rate of 102% of the fair value of the loaned securities (or 105% of the fair value of the loaned securities when the collateral and loaned securities are denominated in non-U.S. currencies) including accrued investment income and is monitored and maintained by the lending agent. Such collateral is reinvested and is reflected as "Short-term investment of funds received under securities lending agreements, at fair value." At December 31, 2007, the fair value and amortized cost of fixed maturities and short-term investments pledged under securities lending agreements were $1.46 billion and $1.44 billion, respectively, while collateral received totaled $1.5 billion at fair value and amortized cost. At December 31, 2006, the fair value and amortized cost of fixed maturities and short-term investments pledged under securities lending agreements were $860.8 million and $854.8 million, respectively, while collateral received totaled $891.4 million at fair value and amortized cost.

        As part of our investment strategy, we seek to establish a level of cash and highly liquid short-term and intermediate-term securities which, combined with expected cash flow, is believed by us to be adequate to meet our foreseeable payment obligations. Our investment strategy allows for the use of derivative securities. Derivative instruments may be used to enhance investment performance, replicate investment positions or manage market exposures and duration risk that would be allowed under our investment guidelines if implemented in other ways. The fair values of those derivatives are based on quoted market prices. At December 31, 2007 and 2006, the notional value of the net long position for equity futures was $91.2 million and $78.6 million, respectively. At December 31, 2007, the notional value of the net long position for Treasury note futures was $61.7 million, compared to a net short position of $35.2 million at December 31, 2006. For 2007, we recorded net realized losses of $2.0 million related to changes in the fair value of all futures contracts, compared to net realized gains of $2.1 million for 2006. At December 31, 2007, the carrying value and fair value of all futures contracts was $0.8 million, compared to $0.3 million at December 31, 2006.

        Our portfolio also includes investments in other asset sectors, such as alternative investment funds that primarily include funds that invest in investment grade and non-investment grade fixed income

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securities; equity securities which include certain investments in mutual funds and other preferred stocks; and privately held securities which include our investment in Aeolus LP. In future periods, we may allocate substantial additional funds to alternate investments in order to increase the diversification of our portfolio and to maximize returns within a defined level of risk over a longer period of time. Certain of these alternative investments may be accounted for under the equity method, which could increase the volatility of our reported earnings. See note 10, "Transactions with Related Parties," of the notes accompanying our consolidated financial statements for further details on the Company's investment in Aeolus, L.P. Our unfunded investment commitments related to other investments totaled approximately $150.2 million at December 31, 2007. The commitments were primarily to alternative investment funds that invest in investment grade and non-investment grade fixed income securities.

Calculation of Book Value Per Common Share

        The following table presents the calculation of book value per common share and the impact of transactions under the share repurchase program on book value per common share at December 31, 2007 and 2006:

 
   December 31,
  
(U.S. dollars in thousands, except share data)

   2007