Basis of Presentation and Significant Accounting Policies	12 Months Ended
Dec. 31, 2025
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Presentation and Significant Accounting Policies	Basis of Presentation and Significant Accounting Policies Basis of Presentation White Mountains Insurance Group, Ltd. (the “Company” or the “Registrant”) is an exempted Bermuda limited liability company whose principal businesses are conducted through its subsidiaries and other affiliates. The Company’s headquarters is located at 26 Reid Street, Hamilton, Bermuda HM 11, its principal executive office is located at 23 South Main Street, Suite 3B, Hanover, New Hampshire 03755-2053 and its registered office is located at Clarendon House, 2 Church Street, Hamilton, Bermuda HM 11. The Company’s website is www.whitemountains.com. The information contained on the Company’s website is not incorporated by reference into, and is not a part of, this report. The accompanying consolidated financial statements have been prepared in accordance with generally accepted accounting principles in the United States (“GAAP”) and include the accounts of the Company, its subsidiaries (collectively with the Company, “White Mountains”) and other entities required to be consolidated under GAAP. Certain amounts in the prior period financial statements have been reclassified to conform to the current presentation. Consolidation Principles Under GAAP, the Company is required to consolidate any entity in which it holds a controlling financial interest. A controlling financial interest is usually in the form of an investment representing the majority of the subsidiary’s voting interests. However, a controlling financial interest may also arise from a financial interest in a variable interest entity (“VIE”) through arrangements that do not involve ownership of voting interests. The Company consolidates a VIE if it determines that it is the primary beneficiary. The primary beneficiary is defined as the entity that holds a variable interest that gives it both the power to direct the VIE’s activities that most significantly impact its economic performance and the obligation to absorb losses of, or the right to receive returns from, the VIE that could potentially be significant to the VIE. See Note 16 — “Variable Interest Entities.” Intercompany transactions have been eliminated in consolidation. Use of Estimates The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities as of the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. Actual results could differ from those estimates. Reportable Segments As of December 31, 2025, White Mountains conducted its operations through four reportable segments: (1) Ark/WM Outrigger, (2) HG Global, (3) Kudu and (4) Distinguished, with its remaining operating businesses, holding companies and other assets included in Other Operations. White Mountains has made its segment determination based on consideration of the following criteria: (i) the nature of the business activities of each of the Company’s subsidiaries and affiliates; (ii) the manner in which the Company’s subsidiaries and affiliates are organized; (iii) the existence of primary managers responsible for specific subsidiaries and affiliates; and (iv) the organization of information provided to the Company’s chief operating decision maker (“CODM”) and its Board of Directors. See Note 15 — “Segment Information.” The Ark/WM Outrigger segment consists of Ark Insurance Holdings Limited and its subsidiaries (collectively, “Ark”) and Outrigger Re Ltd. Segregated Account 2023-1 (“WM Outrigger Re”) (collectively with Ark, “Ark/WM Outrigger”). Ark is a specialty property and casualty insurance and reinsurance company that offers a wide range of niche insurance and reinsurance products, including property, specialty, marine & energy, casualty and accident & health. Ark underwrites select coverages through Lloyd’s Syndicates 4020 and 3902 and Additional Central Settlement Number (“ACSN”) 3832 (collectively, the “Syndicates”) and its wholly-owned subsidiary Group Ark Insurance Limited (“GAIL”). White Mountains acquired a controlling ownership interest in Ark on January 1, 2021 (the “Ark Transaction”). As of December 31, 2025 and 2024, White Mountains owned 72.1% of Ark on a basic shares outstanding basis (61.9% after taking account of management’s equity incentives). The remaining shares are owned by current and former employees of Ark. In the future, management rollover shareholders could earn additional shares in Ark if and to the extent that White Mountains achieves certain thresholds for its multiple of invested capital (“MOIC”) return. If fully earned, these shares would represent an additional 12.3% of the shares outstanding as of December 31, 2025. The liability related to these additional shares is recorded as contingent consideration. Outrigger Re Ltd. is a Bermuda special purpose insurer and segregated accounts company that provides collateralized reinsurance protection on Ark’s Bermuda global property catastrophe excess of loss portfolio. As of December 31, 2025 and 2024, White Mountains owned 100.0% of the preferred equity of its segregated cell, WM Outrigger Re. White Mountains consolidates WM Outrigger Re in its financial statements. See Note 2 — “Significant Transactions.” The HG Global segment consists of HG Global Ltd. and its wholly-owned subsidiaries (collectively, “HG Global”) and, prior to its deconsolidation on July 1, 2024, the consolidated results of Build America Mutual Assurance Company (“BAM”). See Note 2 — “Significant Transactions.” HG Global was established to fund the startup of BAM and, through its reinsurance subsidiary, HG Re Ltd. (“HG Re”), to provide first-loss reinsurance protection of up to 15%-of-par outstanding for each policy assumed from BAM. HG Global, together with its subsidiaries, funded the initial capitalization of BAM through the purchase of $503.0 million of surplus notes issued by BAM (the “BAM Surplus Notes”). As of December 31, 2025 and 2024, White Mountains owned 96.9% of HG Global’s preferred equity and 88.4% of its common equity. White Mountains does not have an ownership interest in BAM. However, through June 30, 2024, White Mountains was required to consolidate BAM’s results in its financial statements because BAM is a VIE for which White Mountains was the primary beneficiary. BAM’s results were all attributed to noncontrolling interests. On July 1, 2024, HG Re and BAM amended the terms of the first-loss reinsurance treaty (“FLRT”) with respect to certain governance rights held by HG Re. As a result, and in combination with other governance changes at BAM, White Mountains concluded that it no longer has the power to direct BAM’s activities that most significantly impact its economic performance and is no longer BAM’s primary beneficiary. Accordingly, effective July 1, 2024, White Mountains no longer consolidates BAM. Through June 30, 2024, BAM’s results of operations were presented within the HG Global segment. See Note 2 — “Significant Transactions.” The Kudu segment consists of Kudu Investment Management, LLC and its subsidiaries (collectively, “Kudu”). Kudu provides capital solutions for boutique asset and wealth managers for a variety of purposes including generational ownership transfers, management buyouts, acquisition and growth finance and legacy partner liquidity. Kudu also provides strategic advice to managers from time to time. Kudu’s capital solutions are generally structured as noncontrolling equity interests in the form of revenue and earnings participation contracts (“Participation Contracts”) and designed to generate immediate cash yields. As of December 31, 2025 and 2024, White Mountains owned 91.2% and 90.4% of Kudu’s basic units outstanding (77.9% and 77.0% on a fully-diluted/fully-converted basis, taking account of management’s equity incentives). The Distinguished segment consists of WM Phoenix Parent, L.P. and its subsidiaries d/b/a Distinguished Programs (collectively, “Distinguished”). Distinguished is a full-service MGA and program administrator for specialty property and casualty insurance. Distinguished places insurance across a diversified portfolio of programs broadly grouped into two verticals. The ScaleCo vertical consists of established programs, primarily focused on real estate and hospitality end markets. The GrowthCo vertical consists of start-up programs, focused on a diversified set of specialty property and casualty insurance products across multiple industries. On behalf of its insurance carrier partners, Distinguished typically manages all aspects of the placement process, including product development, marketing, underwriting and policy issuance. Distinguished earns commissions based on the volume and profitability of the insurance that it places. Distinguished does not retain insurance risk. On September 2, 2025, White Mountains acquired a controlling financial interest in Distinguished. See Note 2 — “Significant Transactions.” As of December 31, 2025, White Mountains owned 55.5% of Distinguished on a basic units outstanding basis (43.6% on a fully-diluted/fully-converted basis, taking account of management’s equity incentives). White Mountains’s other operations consist of the Company and its wholly-owned subsidiary, White Mountains Capital, LLC (“WM Capital”), its other intermediate holding companies, its wholly-owned investment management subsidiary, White Mountains Advisors LLC (“WM Advisors”), investment assets managed by WM Advisors, its interests in Bamboo Ide8 Insurance Services LLC (“Bamboo MGA”) and its subsidiaries through a special purpose vehicle (the “Bamboo SPV”), MediaAlpha, Inc. (“MediaAlpha”), DavidShield PassportCard Ltd. and its subsidiaries (collectively, “PassportCard/DavidShield”), BroadStreet Partners, Inc. (“BroadStreet”) through a special purpose vehicle (the “BroadStreet SPV”), Elementum Holdings LP (“Elementum”), White Mountains Partners LLC (“WTM Partners”), Enterprise Electric, LLC d/b/a Enterprise Solutions (“Enterprise Solutions”), two special purpose collateralized reinsurance vehicles that provide reinsurance capacity to Bamboo (the “Bamboo CRVs”), certain other consolidated and unconsolidated entities (“Other Operating Businesses”) and certain other assets (collectively, “Other Operations”). Held for Sale White Mountains recognizes assets and liabilities classified as held for sale at the lower of carrying value on the date the asset is initially classified as held for sale or fair value less costs to sell. At the time of reclassification to held for sale, White Mountains ceases recognizing depreciation and amortization on assets held for sale. On December 5, 2025, White Mountains completed the sale of a controlling financial interest in WM Pierce Holdings, Inc. and its subsidiaries, including Bamboo MGA (collectively, the "Bamboo Group"). As a result of the sale, White Mountains deconsolidated the Bamboo Group on December 5, 2025, and Bamboo is no longer a reportable segment. Through December 5, 2025, Bamboo’s results of operations are presented within the Bamboo segment. See Note 2 — “Significant Transactions.” The Bamboo Group’s assets and liabilities have been presented as held for sale as of December 31, 2024. See Note 20 — “Held for Sale.” Through December 5, 2025, the Bamboo segment consisted of PM Holdings LLC (“Bamboo Holdings”), Bamboo MGA and Ide8 Re, Inc. (the “Bamboo Captive”) (collectively, “Bamboo”). Bamboo is a capital-light, tech- and data-enabled insurance distribution platform providing homeowners’ insurance and related products to the residential property market in California and, beginning in the third quarter of 2025, in Texas. Bamboo operates primarily through Bamboo MGA, its full-service MGA business, where the company manages all aspects of the placement process on behalf of its fronting and reinsurance carrier partners (“Capacity Providers”), including product development, marketing, underwriting, policy issuance and claims oversight, and it earns commissions based on the volume and profitability of the insurance that it places. Bamboo MGA offers both admitted and non-admitted products. Significant Accounting Policies Investment Securities As of December 31, 2025 and 2024, White Mountains’s invested assets consisted of securities and other investments held for general investment purposes. White Mountains’s portfolio of investment securities held for general investment purposes consists of fixed maturity investments, short-term investments, common equity securities, its investment in MediaAlpha and other long-term investments. Short-term investments consist of interest-bearing money market funds, certificates of deposit and other fixed maturity securities, which at the time of purchase, mature or become available for use within one year. Short-term investments are carried at fair value, which approximated amortized or accreted cost as of December 31, 2025 and 2024. Other long-term investments consist primarily of unconsolidated entities, including Kudu’s Participation Contracts, the Bamboo SPV, PassportCard/DavidShield and the BroadStreet SPV, as well as private equity funds and hedge funds, a bank loan fund and Lloyd’s of London (“Lloyd’s”) trust deposits. White Mountains’s portfolio of fixed maturity investments, including those within short-term investments, are classified as trading securities. Trading securities are reported at fair value as of the balance sheet date. White Mountains’s portfolio of common equity securities, its investment in MediaAlpha and other long-term investments are measured at fair value. White Mountains has generally taken the fair value option for its equity method eligible investments. Changes in net unrealized investment gains (losses) are reported pre-tax in revenues. Realized investment gains (losses) are accounted for using the specific identification method and are reported pre-tax in revenues. Premiums and discounts on all fixed maturity investments are amortized and accreted to income over the anticipated life of the investment. Income on mortgage and asset-backed securities is recognized using an effective yield based on anticipated prepayments and the estimated economic life of the securities. When actual prepayments differ significantly from anticipated prepayments, the estimated economic life is recalculated, and the remaining unamortized premium or discount is amortized prospectively over the remaining economic life. Fair value is defined as the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants (an exit price) at a particular measurement date. Fair value measurements are categorized into a hierarchy that distinguishes between inputs based on market data from independent sources (observable inputs) and a reporting entity’s internal assumptions based upon the best information available when external market data is limited or unavailable (unobservable inputs). Quoted prices in active markets for identical assets have the highest priority (“Level 1”), followed by observable inputs other than quoted prices including prices for similar but not identical assets or liabilities (“Level 2”) and unobservable inputs, including the reporting entity’s estimates of the assumptions that market participants would use, having the lowest priority (“Level 3”). Assets and liabilities carried at fair value include White Mountains’s investment portfolio and derivative instruments. Valuation of assets and liabilities measured at fair value require management to make estimates and apply judgment to matters that may carry a significant degree of uncertainty. In determining its estimates of fair value, White Mountains uses a variety of valuation approaches and inputs. Whenever possible, White Mountains estimates fair value using valuation methods that maximize the use of quoted market prices or other observable inputs. Where appropriate, assets and liabilities measured at fair value have been adjusted for the effect of counterparty credit risk. White Mountains uses outside pricing services and brokers to assist in determining fair values. The outside pricing services White Mountains uses have indicated that they will only provide prices where observable inputs are available. Level 1 Measurements Investments valued using Level 1 inputs include White Mountains’s fixed maturity investments, primarily investments in U.S. Treasuries and short-term investments, which include U.S. Treasury Bills, common equity securities and its investment in MediaAlpha. For investments in active markets, White Mountains uses the quoted market prices provided by outside pricing services to determine fair value. Level 2 Measurements Investments valued using Level 2 inputs include fixed maturity investments which have been disaggregated into classes, including debt securities issued by corporations, municipal obligations, foreign government and agency obligations, mortgage and asset-backed securities and collateralized loan obligations. Investments valued using Level 2 inputs also include certain international listed common equity funds, which White Mountains values using the fund manager’s published net asset value (“NAV”) to account for the difference in market exchange close times, and certain derivative instruments. In circumstances where quoted market prices are unavailable or are not considered reasonable, White Mountains estimates the fair value using industry standard pricing methodologies and observable inputs such as benchmark yields, reported trades, broker-dealer quotes, issuer spreads, benchmark securities, bids, offers, credit ratings, prepayment speeds, reference data including research publications and other relevant inputs. Given that many fixed maturity investments do not trade on a daily basis, the outside pricing services evaluate a wide range of fixed maturity investments by regularly drawing parallels from recent trades and quotes of comparable securities with similar features. The characteristics used to identify comparable fixed maturity investments vary by asset type and take into account market convention. White Mountains’s process to assess the reasonableness of the market prices obtained from the outside pricing sources covers substantially all of its fixed maturity investments and includes, but is not limited to, the evaluation of pricing methodologies and a review of the pricing services’ quality control procedures on at least an annual basis, a comparison of invested asset prices obtained from alternate independent pricing vendors on at least a semi-annual basis, monthly analytical reviews of certain prices and a review of the underlying assumptions utilized by the pricing services for select measurements on an ad hoc basis throughout the year. White Mountains also performs back-testing of selected investment sales activity to determine whether there are any significant differences between the market price used to value the security prior to sale and the actual sale price of the security on an ad-hoc basis throughout the year. Prices provided by the pricing services that vary by more than $0.5 million and 5% from the expected price based on these assessment procedures are considered outliers, as are prices that have not changed from period to period and prices that have trended unusually compared to market conditions. In circumstances where the results of White Mountains’s review process does not appear to support the market price provided by the pricing services, White Mountains challenges the vendor provided price. If White Mountains cannot gain satisfactory evidence to support the challenged price, White Mountains will rely upon its own internal pricing methodologies to estimate the fair value of the security in question. The valuation process described above is generally applicable to all of White Mountains’s fixed maturity investments. The techniques and inputs specific to asset classes within White Mountains’s fixed maturity investments for Level 2 securities that use observable inputs are as follows: Debt Securities Issued by Corporations The fair value of debt securities issued by corporations is determined from a pricing evaluation technique that uses information from market sources and integrates relative credit information, observed market movements and sector news. Key inputs include benchmark yields, reported trades, broker-dealer quotes, issuer spreads, two-sided markets, benchmark securities, bids, offers and reference data including sector, coupon, credit quality ratings, duration, credit enhancements, early redemption features and market research publications. Municipal Obligations The fair value of municipal obligations is determined from a pricing evaluation technique that uses information from market makers, brokers-dealers, buy-side firms and analysts along with general market information. Key inputs include benchmark yields, reported trades, issuer financial statements, material event notices and new issue data, as well as broker-dealer quotes, issuer spreads, two-sided markets, benchmark securities, bids, offers and reference data including type, coupon, credit quality ratings, duration, credit enhancements, geographic location and market research publications. Foreign Government and Agency Obligations The fair value of foreign government and agency obligations is determined from a pricing evaluation technique that uses information from data sources in each respective country, including active market makers and inter-dealer brokers. Key inputs include benchmark yields, reported trades, broker-dealer quotes, issuer spreads, two-sided markets, benchmark securities, bids, offers, local exchange prices, foreign currency exchange rates and reference data including coupon, credit quality ratings, duration and market research publications. Mortgage and Asset-Backed Securities and Collateralized Loan Obligations The fair value of mortgage and asset-backed securities and collateralized loan obligations is determined from a pricing evaluation technique that uses information from market sources and leveraging similar securities. Key inputs include benchmark yields, reported trades, underlying tranche cash flow data, collateral performance, plus new issue data, as well as broker-dealer quotes, issuer spreads, two-sided markets, benchmark securities, bids, offers and reference data including issuer, vintage, loan type, collateral attributes, prepayment speeds, default rates, recovery rates, cash flow stress testing, credit quality ratings and market research publications. Level 3 Measurements Fair value estimates for investments that trade infrequently and have few or no quoted market prices or other observable inputs are classified as Level 3 measurements. Investments valued using Level 3 fair value estimates are based upon unobservable inputs and include investments in certain fixed maturity investments, common equity securities and other long-term investments where quoted market prices or other observable inputs are unavailable or are not considered reliable or reasonable. Level 3 valuations are generated from techniques that use assumptions not observable in the market. These unobservable inputs reflect White Mountains’s assumptions of what market participants would use in valuing the investment. In certain circumstances, investment securities may start out as Level 3 when they are originally issued, but as observable inputs become available in the market, they may be reclassified to Level 2. Transfers of securities between levels are based on investments held as of the beginning of the period. Other Long-Term Investments As of December 31, 2025, $1,814.4 million of White Mountains’s other long-term investments were classified as Level 3 investments in the GAAP fair value hierarchy, including Kudu’s Participation Contracts, the Bamboo SPV, PassportCard/DavidShield and certain other unconsolidated entities. The determination of the fair value of these securities involves significant management judgment, and the use of valuation analyses and assumptions that are inherently subjective and uncertain. White Mountains may use a variety of valuation techniques to determine fair value depending on the nature of the investment, including a discounted cash flow analysis, market multiple approach, cost approach and/or liquidation analysis. On an ongoing basis, White Mountains also considers qualitative changes in facts and circumstances, which may impact the valuation of its unconsolidated entities, including economic and market changes in relevant industries, changes to the entity’s capital structure, business strategy and key personnel and any recent transactions. On a quarterly basis, White Mountains evaluates the most recent qualitative and quantitative information of the business and completes a fair valuation analysis for all other long-term investments classified as Level 3 investments. Periodically, and at least on an annual basis, White Mountains uses a third-party valuation firm to complete an independent valuation analysis of significant unconsolidated entities. Other Long-term Investments - NAV As of December 31, 2025, $1,110.4 million of White Mountains’s other long-term investments were measured at fair value using NAV as a practical expedient, including the BroadStreet SPV, private equity funds and hedge funds, a bank loan fund, Lloyd’s trust deposits and insurance-linked securities (“ILS”) funds. Investments for which fair value is measured using NAV as a practical expedient are not classified within the fair value hierarchy. White Mountains employs a number of procedures to assess the reasonableness of the fair value measurements for other long-term investments measured at NAV, including obtaining and reviewing interim unaudited and annual audited financial statements as well as periodically discussing the valuations and methodologies used to value the underlying investments of each fund with fund managers. However, since fund managers do not provide sufficient information to evaluate the pricing methods and inputs for each underlying investment, White Mountains considers the valuation inputs to be unobservable. The fair value of White Mountains’s other long-term investments measured at NAV are generally determined using the fund manager’s NAV. Certain other long-term investments measured at NAV may be reported to White Mountains on a lag. In these circumstances, the NAV of such investments is adjusted to account for any applicable contributions, distributions, known transactions and/or pricing estimates provided by the fund manager through White Mountains’s reporting date. BAM Surplus Notes Prior to the deconsolidation of BAM on July 1, 2024, the BAM Surplus Notes, including accrued interest receivable, were classified as intercompany notes carried at nominal value, which eliminated in consolidation. Upon deconsolidation, White Mountains elected the fair value option for the BAM Surplus Notes. White Mountains values the BAM Surplus Notes each quarter using a discounted cash flow analysis. The BAM Surplus Notes are classified as a Level 3 measurement. Upon election of the fair value option, White Mountains made the accounting policy election to present the interest income from the BAM Surplus Notes separately from the change in fair value of the BAM Surplus Notes. See Note 10 — “Municipal Bond Guarantee Reinsurance.” Cash and Restricted Cash Cash includes amounts on hand and demand deposits with banks and other financial institutions. Amounts presented in the statement of cash flows are shown net of balances acquired and sold in the purchase or sale of the Company’s consolidated subsidiaries. Cash balances that are not immediately available for general corporate and operating purposes are classified as restricted. Derivatives From time to time, White Mountains holds derivative financial instruments for risk management purposes. White Mountains recognizes all derivatives as either assets or liabilities, measured at fair value, on its consolidated balance sheet. Changes in the fair value of derivative instruments that meet the criteria for hedge accounting are recognized in other comprehensive income (loss) and reclassified into current period pre-tax income (loss) when the hedged items are recognized therein. Changes in the fair value of derivative instruments that do not meet the criteria for hedge accounting are recognized in current period pre-tax income (loss). As of December 31, 2025, White Mountains holds interest rate cap derivative instruments that do not meet the criteria for hedge accounting. See Note 9 — “Derivatives.” Property and Casualty Insurance and Reinsurance Ark writes a diversified portfolio of reinsurance and insurance products, including property, specialty, marine & energy, casualty and accident & health. Ark accounts for insurance and reinsurance policies that it writes in accordance with ASC 944, Financial Services - Insurance. Ark’s premiums written comprise premiums on insurance contracts incepted during the year as well as premium adjustments related to prior underwriting years. Insurance premiums are recognized as revenues over the loss exposure or coverage period. In most cases, premiums are earned ratably over the term of the contract, with unearned premiums calculated on a monthly pro-rata basis. Catastrophe premiums are earned in proportion to the insurance protection provided. Premiums earned are presented net of amounts ceded to reinsurers. Insurance premiums receivable, representing amounts due from insureds, are presented net of an allowance for uncollectible premiums, including expected credit losses. The allowance is based upon Ark’s ongoing review of amounts outstanding, historical loss data, including delinquencies and write-offs, current and forecasted economic conditions and other relevant factors. Credit risk is partially mitigated by Ark’s ability to cancel the policy if the policyholder does not pay the premium. Deferred acquisition costs comprise commission and brokerage fees and taxes which are directly attributable to and vary with the production of business. These costs are deferred and amortized to the extent that they relate to successful contract acquisitions over the applicable premium recognition period as acquisition expenses. Deferred acquisition costs are limited to the amount expected to be recovered from future earned premiums and anticipated investment income. A premium deficiency is recognized if the sum of expected loss and loss adjustment expenses (“LAE”), expected dividends to policyholders, unamortized acquisition costs and maintenance costs exceeds related unearned premiums and anticipated investment income. A premium deficiency is recognized by charging any unamortized acquisition costs to expense to the extent required in order to eliminate the deficiency. If the premium deficiency exceeds unamortized acquisition costs, then a liability is accrued for the excess deficiency. Loss and LAE are charged against income as incurred. Loss and LAE reserves, including estimates for amounts incurred but not reported (“IBNR”), are based on management’s best estimate of the ultimate costs to settle claims, including the effects of inflation and other societal and economic factors. Loss and LAE reserves are presented net of estimated salvage and subrogation recoveries, if applicable. Such estimates are regularly reviewed and updated, and any resulting adjustments are reflected in current results of operations. The process of estimating loss and LAE reserves involves a considerable degree of judgment by management, and the ultimate amount of expense to be incurred could be considerably greater than or less than the amounts currently reflected in the financial statements. See Note 5 — “Loss and Loss Adjustment Expense Reserves.” As part of its enterprise risk management function, Ark purchases reinsurance for risk mitigation purposes. Ark utilizes reinsurance and retrocessional agreements to reduce earnings volatility, protect capital, limit concentration and accumulation risk and manage within its overall internal risk tolerances and/or those set and agreed by regulators, ratings agencies and Lloyd’s. Ark also enters into reinsurance and retrocessional agreements to reduce its exposures on individual risks and enable it to underwrite policies with higher limits where Ark believes this has a broader business benefit. Ark seeks to protect its downside risk from catastrophes and large loss events by purchasing reinsurance, including excess of loss protections, aggregate covers and industry loss warranties. Ark also considers alternative structures such as collateralized reinsurance, retrocessional reinsurance and catastrophe bonds. The purchase of reinsurance does not discharge Ark from its primary liability for the full value of its policies, and thus the collectability of balances due from Ark’s reinsurers is critical to its financial strength. Ark monitors the financial strength and ratings of its reinsurers on an ongoing basis. See Note 6 — “Third-Party Reinsurance.” Reinsurance recoverables represent paid loss and LAE, case reserves and IBNR reserves ceded to reinsurers under reinsurance treaties. Amounts recoverable from reinsurers are estimated in a manner consistent with the associated claims liability. Ark reports its reinsurance recoverables net of an allowance for estimated uncollectible reinsurance, including expected credit losses and coverage disputes. The allowance is based upon Ark’s ongoing review of amounts outstanding, length of collection periods, changes in reinsurer credit standing, disputes, applicable coverage defenses and other relevant factors. Municipal Bond Guarantee Reinsurance As of July 1, 2024, White Mountains no longer consolidates BAM. Through June 30, 2024, BAM’s results of operations are presented within the HG Global segment. The FLRT and all the contracts issued by BAM are accounted for as insurance contracts under ASC 944-605, Financial Guarantee Insurance Contracts. For capital appreciation bonds, par is adjusted to the estimated equivalent par value for current interest paying bonds. Prior to the deconsolidation of BAM, HG Re’s reinsurance balances under the FLRT eliminated in White Mountains’s consolidated financial statements. See Note 10 — “Municipal Bond Guarantee Reinsurance.” Premiums are generally received upfront and an unearned premium reserve, equal to the amount of the premium received, is established at contract inception. Premiums are recognized in revenue over the period of the contracts in proportion to the amount of insurance protection provided using a constant rate. The constant rate is calculated based on the relationship between the par outstanding in a given reporting period compared with the sum of each of the par amounts outstanding for all periods. HG Re’s insurance premiums receivable represents amounts due from BAM. Installment premiums are measured at the present value of contractual premiums, discounted at the risk-free rate, which is set at the inception of the insurance contract. HG Re’s deferred acquisition costs represent the ceding commission paid to BAM. These costs are deferred and amortized to the extent that they relate to successful contract acquisitions over the applicable premium recognition period as acquisition expenses. Deferred acquisition costs are limited to the amount expected to be recovered from future earned premiums and anticipated investment income. A premium deficiency is recognized if the sum of expected loss and LAE, expected dividends to policyholders, unamortized acquisition costs and maintenance costs exceeds related unearned premiums and anticipated investment income. A premium deficiency is recognized by charging any unamortized acquisition costs to expense to the extent required in order to eliminate the deficiency. If the premium deficiency exceeds unamortized acquisition costs, then a liability is accrued for the excess deficiency. Loss reserves are recorded only to the extent that the present value of any payments projected to be made, net of any expected recoveries, exceeds the associated unearned premium reserve. See Note 5 — “Loss and Loss Adjustment Expense Reserves.” Reinsurance Contracts Accounted for as Deposits Reinsurance contracts that do not meet the risk transfer requirements necessary to be accounted for as reinsurance are accounted for using the deposit method. Under the deposit method, ceded premiums paid are not recognized through income but rather treated as a deposit. HG Re is party to an excess of loss reinsurance agreement (the “XOLT”) with BAM. The XOLT is accounted for using deposit accounting as the agreement does not meet the risk transfer requirements necessary to be accounted for as reinsurance. Accordingly, any financing revenues related to the XOLT are recorded in other revenues. See Note 10 — “Municipal Bond Guarantee Reinsurance.” Revenue Recognition Kudu’s revenues are primarily generated from Participation Contracts, which are generally noncontrolling equity interests in revenue and earnings participation contracts with asset and wealth management firms. Kudu’s Participation Contracts are measured at fair value with the change therein recognized within net realized and unrealized investment gains (losses). Distributions from Kudu’s managers are recognized through investment income when Kudu’s right to receive payment has been established and can be reliably measured, which generally occurs on a quarterly basis in accordance with the terms of the Participation Contracts. Bamboo’s revenues consist primarily of commission and fee revenues for placement of insurance policies. Commission and fee revenues are measured based on the contractual rates with insurance carriers, net of any amounts expected to be uncollectible and any amounts associated with expected policy cancellations and adjustments, and are recognized when contractual performance obligations have been fulfilled. Bamboo’s primary contractual performance obligations are generally satisfied upon the issuance of an insurance policy. Bamboo’s premiums, commissions and fees receivable consist of insurance premiums and fees receivable from customers and commissions receivable from insurance carriers, net of a provision for amounts estimated to be uncollectible and any amounts associated with expected policy cancellations and adjustments. Distinguished’s revenues consist primarily of commission and fee revenues related to its placement of insurance policies. Commission revenues are measured based on the contractual rates with its insurance carriers, net of any amounts expected to be uncollectible and any amounts associated with expected policy cancellations and adjustments, and are recognized when contractual performance obligations have been fulfilled. Distinguished also earns fee revenues, primarily related to risk management services provided to certain insureds, which are recognized when contractual performance obligations have been fulfilled. Distinguished’s primary contractual performance obligations are generally satisfied upon the issuance of an insurance policy. Distinguished’s premiums, commissions and fees receivable consist of insurance premiums and fees receivable from insureds and commissions receivable from insurance carriers, net of a provision for amounts estimated to be uncollectible and any amounts associated with expected policy cancellations and adjustments. Premiums receivable are collected on behalf of Distinguished’s insurance carriers. Distinguished’s premiums and commissions payable consist of insurance premiums payable to insurance carriers and commissions payable to sub-agents and brokers. Other Operations recognizes commissions and fee revenues as well as other revenues when it has satisfied its performance obligations. Enterprise Solutions’s revenues consist primarily of construction revenues from specialty electrical contracting services provided to commercial and institutional customers. Enterprise Solutions’s billings are generally based on contractual terms and may not coincide with its progress in a project. Construction revenues, which are presented within other revenues, are recognized over time using the cost-to-cost percentage of completion input method, based on the ratio of contract costs incurred to date compared to total estimated contract costs. Contract costs incurred to date and expected total contract costs are continuously monitored during the term of the contract. Enterprise Solutions records accounts receivable, which are presented within other assets, for amounts billed to the customer, net of a provision for amounts estimated to be uncollectible. If the recognized revenue is greater than the amount billed to the customer, a contract asset is recorded within other assets. Contract assets also include amounts billed under retainage provisions that cannot be collected until the contract work has been completed and approved. If the amount billed to the customer is greater than the recognized revenue, a contract liability is recorded within other liabilities. Broker Commission Expenses and Cost of Sales Bamboo’s broker commission expenses consist of commissions paid to sub-agents and brokers. Broker commission expense is measured in accordance with contractual terms and recognized when incurred, which is generally at the policy issuance date. Distinguished’s broker commission expenses consist of commissions paid to sub-agents and brokers. Broker commission expense is measured in accordance with contractual terms and recognized when incurred, which is generally at the policy issuance date. Other Operations recognizes cost of sales consisting of salaries and related expenses, professional services and marketing and advertising expenses directly related to sales generation. These expenses are recognized as incurred. Incentive Compensation White Mountains’s Long-Term Incentive Plan (the “WTM Incentive Plan”) provides for grants of various types of share-based and non-share-based incentive awards to key employees of White Mountains. Non-share-based awards are recognized over the related service periods based on management’s best estimate of the amounts at which the awards are expected to be paid. Share-based compensation which is typically settled in cash, such as performance shares, is classified as a liability-type award. The compensation cost for liability-classified awards is measured initially at the grant date fair value and remeasured each reporting period until settlement. The compensation cost for equity-classified awards expected to be settled in shares, such as restricted shares, is measured at the original grant date fair value of the award. The compensation cost for all awards is recognized for the vested portion of the awards over the related service periods. See Note 12 — “Employee Share-Based Incentive Compensation Plans.” Income Taxes White Mountains has subsidiaries and branches that operate in various jurisdictions around the world and are subject to tax in the jurisdictions in which they operate. As of December 31, 2025, the primary jurisdictions in which the Company’s subsidiaries and branches operate and were subject to tax include Israel, Luxembourg, the United Kingdom and the United States. Income earned or losses generated by companies outside the United States are generally subject to an overall effective tax rate lower than that imposed by the United States. Deferred tax assets and liabilities are recorded when a difference between the carrying amounts of assets and liabilities for financial reporting purposes and the amounts for tax purposes exists, or there are other temporary differences. The deferred tax asset or liability is recorded based on tax rates expected to be in effect when the difference reverses. Deferred tax assets represent amounts available to reduce income taxes payable in future periods. White Mountains records a valuation allowance against deferred tax assets if it becomes more likely than not that all or a portion of a deferred tax asset will not be realized. Changes in valuation allowances from period to period are included in income tax expense in the period of change. See Note 8 — “Income Taxes.” Leases White Mountains has entered into lease agreements, primarily for office space and equipment. These leases are classified as operating leases, with lease expense recognized on a straight-line basis over the term of the lease. Lease assets and liabilities are not recorded for leases with a term at inception of one year or less. Lease incentives, such as free rent or landlord reimbursements for leasehold improvements, are recognized at lease inception and amortized on a straight-line basis over the term of the lease. Lease expense and the amortization of leasehold improvements are recognized within general and administrative expenses. Lease payments related to options to extend or renew the lease term are excluded from the calculation of lease liabilities unless White Mountains is reasonably certain of exercising those options. As of December 31, 2025 and 2024, the right-of-use assets were $51.2 million and $32.6 million, and the lease liabilities were $56.2 million and $35.5 million. Noncontrolling Interests Noncontrolling interests consist of the ownership interests of noncontrolling shareholders in consolidated entities. White Mountains has both redeemable and nonredeemable noncontrolling interests. Noncontrolling interests with redemption features that are not within White Mountains’s control are classified as redeemable noncontrolling interests, which are considered temporary equity and presented as mezzanine equity on the balance sheet. Redeemable noncontrolling interests are excluded from White Mountains’s total equity. The redeemable noncontrolling interests relate to Distinguished. Noncontrolling interests that do not have any redemption features are classified as nonredeemable noncontrolling interests, which are considered permanent equity and included in White Mountains’s total equity on the balance sheet. Nonredeemable noncontrolling interests are presented separately from White Mountains’s common shareholders’ equity. See Note 13 — “Common Shareholders’ Equity and Noncontrolling Interests.” Comprehensive income (loss) is attributable to both redeemable and nonredeemable noncontrolling interests and is presented net of related income taxes in the statements of operations and comprehensive income (loss). In addition, White Mountains recognizes an adjustment to the carrying value of the redeemable noncontrolling interests to the extent that the carrying value is below the redemption value. The adjustment for redeemable noncontrolling interests is recognized through White Mountains’s common shareholders’ equity. When calculating basic and diluted earnings per share, the adjustment for redeemable noncontrolling interests is treated as being akin to a dividend and presented as an adjustment to net income (loss) attributable to White Mountains’s common shareholders. Foreign Currency Exchange The functional currencies for White Mountains’s non-U.S. based subsidiaries are measured, in most instances, using currencies other than the U.S. dollar. Net foreign currency exchange gains and losses arising from the translation of functional currencies are generally reported in shareholders’ equity, in accumulated other comprehensive income (loss). White Mountains also invests in securities denominated in foreign currencies. Assets and liabilities recorded in these foreign currencies are translated into U.S. dollars at exchange rates in effect at the balance sheet date, and revenues and expenses are converted using the weighted average exchange rates for the period. As of December 31, 2025 and 2024, White Mountains had unrealized foreign currency translation gains (losses) of $0.8 million and $(1.7) million recorded in accumulated other comprehensive income (loss) on its consolidated balance sheet. Fair Value Measurements Fair value measurements are categorized into a hierarchy that distinguishes between inputs based on market data from independent sources (observable inputs) and a reporting entity’s internal assumptions based upon the best information available when external market data is limited or unavailable (unobservable inputs). Quoted prices in active markets for identical assets or liabilities have the highest priority (Level 1), followed by observable inputs other than quoted prices, including prices for similar but not identical assets or liabilities (Level 2) and unobservable inputs, including the reporting entity’s estimates of the assumptions that market participants would use, having the lowest priority (Level 3). See Note 18 — “Fair Value of Financial Instruments.” Business Combinations White Mountains accounts for purchases of businesses using the acquisition method, which requires the measurement of assets acquired, including other intangible assets, liabilities assumed, including contingent consideration liabilities, and any noncontrolling interests in the acquired entities at their estimated fair values as of the acquisition date. The acquisition date fair values represent management’s best estimates and are based upon established valuation techniques, reasonable assumptions and, where appropriate, valuations performed by independent third parties. In circumstances where additional information is required in order to determine the acquisition date fair value of balance sheet amounts, provisional amounts may be recorded as of the acquisition date and may be subject to subsequent adjustment throughout the measurement period, which is up to one year from the acquisition date. Measurement period adjustments are recognized in the period in which they are determined. The results of operations and cash flows of businesses acquired are included in the consolidated financial statements from the acquisition date. White Mountains accounts for purchases of other intangible assets that do not meet the definition of a business as asset acquisitions. Asset acquisitions are recognized at the amount of consideration paid, which is deemed to equal fair value. Goodwill and Other Intangible Assets Under the acquisition method, White Mountains recognizes and measures the assets acquired, including other intangible assets, at their acquisition date fair values. Goodwill represents the excess of the amount paid to acquire a business over the fair value of identifiable net assets at the acquisition date. Other intangible assets consist primarily of underwriting capacity, agency relationships, customer relationships and trade names. The acquisition date fair values of other intangible assets are estimated using income approach techniques, which use future expected cash flows to develop a discounted present value amount. The multi-period-excess-earnings method estimates fair value using the present value of the incremental after-tax cash flows attributable solely to the other intangible asset over its remaining life. This approach was used to estimate the fair value of other intangible assets associated with the underwriting capacity, agency relationships and customer relationships. The relief-from-royalty method was used to estimate fair value for other intangible assets that relate to rights that could be obtained via a license from a third-party owner. Under this method, the fair value is estimated using the present value of license fees avoided by owning rather than leasing the asset. This technique was used to estimate the fair value of trade names, patents and certain information technology platforms. The with-or-without method estimates the fair value of other intangible assets that provide an incremental benefit. Under this method, the fair value of the other intangible asset is calculated by comparing the value of the entity with and without the other intangible asset. This approach was used to estimate the fair value of non-compete agreements. Goodwill and other intangible assets with indefinite lives are not amortized, but rather are evaluated for impairment on an annual basis, or whenever indications of potential impairment exist. In the absence of any indications of potential impairment, the evaluation of goodwill and indefinite-lived intangible assets is performed no later than the interim period in which the anniversary of the acquisition date falls. White Mountains initially evaluates goodwill and indefinite-lived intangible assets using a qualitative approach (step zero) to determine whether it is more likely than not that the implied fair value is greater than the carrying value. If the results of the qualitative evaluation indicate that it is more likely than not that the carrying value of goodwill or the indefinite-lived intangible assets exceeds the implied fair value, White Mountains performs a quantitative analysis to compare the fair value with the carrying value. If the carrying value exceeds the estimated fair value, then an impairment charge is recognized through current period pre-tax income (loss). Other intangible assets with finite lives are initially measured at their acquisition date fair values and subsequently amortized over their economic lives. Finite-lived intangible assets are presented net of accumulated amortization on the balance sheet. Finite-lived intangible assets are reviewed for impairment when events occur or there are changes in circumstances indicating that their carrying value may exceed fair value. An impairment exists when the carrying value of a finite-lived intangible asset exceeds the fair value. See Note 4 — “Goodwill and Other Intangible Assets.” Contingent Consideration Liabilities The consideration for the Ark Transaction included potential future payments to management rollover shareholders, which are payable in a variable number of shares, if and to the extent that White Mountains achieves certain MOIC return thresholds. This additional consideration is generally payable in three equal tranches at MOIC thresholds of 2.0x, 2.5x and 3.0x. If fully earned, these shares would represent an additional 12.3% of the shares outstanding as of December 31, 2025. The liability related to these additional shares is recorded as contingent consideration. Contingent consideration in a business combination that is classified as a liability is measured at fair value on the acquisition date and remeasured to fair value each subsequent reporting period with changes in the fair value recognized through pre-tax income (loss). As a result of the Ark Transaction, White Mountains recognized a contingent consideration liability of $22.5 million as of January 1, 2021. During the years ended December 31, 2025, 2024 and 2023, White Mountains recognized an expense of $173.0 million, $61.3 million and $48.7 million for the change in the fair value of its contingent consideration liability. As of December 31, 2025 and 2024, White Mountains’s contingent consideration liability was $328.3 million and $155.3 million. The contingent consideration liability is a Level 3 measurement. Recently Adopted Accounting Standards Income Taxes White Mountains adopted ASU 2023-09, Income Taxes (Topic 740): Improvements to Income Tax Disclosures (“ASU 2023-09”) effective for its annual disclosures for the year ended December 31, 2025. ASU 2023-09 requires disclosure of disaggregated information about a reporting entity’s effective tax rate reconciliation as well as information on income taxes paid. ASU 2023-09 was adopted retrospectively, including the recasting of previously reported income tax information. See Note 8 — “Income Taxes.” Recently Issued Accounting Standards Disaggregation of Income Statement Expenses In November 2024, the FASB issued ASU 2024-03, Income Statement—Reporting Comprehensive Income—Expense Disaggregation Disclosures (Subtopic 220-40): Disaggregation of Income Statement Expenses (“ASU 2024-03”), which requires additional disclosure of the nature of expenses included in the income statement. ASU 2024-03 requires disclosures about specific types of expenses (i.e., (a) purchases of inventory, (b) employee compensation, (c) depreciation and (d) intangible asset amortization) included in the expense captions presented on the face of the income statement as well as disclosures about selling expenses. ASU 2024-03 does not change the requirements for the presentation of expenses on the income statement. ASU 2024-03 is effective for annual reporting periods beginning after December 15, 2026 and interim reporting periods beginning after December 15, 2027. Early adoption is permitted. Although ASU 2024-03 requires comparative disclosures for all periods presented, reporting entities will be permitted to begin applying the guidance prospectively with the option for retrospective application for all prior periods presented. Accordingly, the new disclosure requirements in ASU 2024-03 are initially required within White Mountains’s Annual Report on Form 10-K for the year ending December 31, 2027. White Mountains is in the process of evaluating the potential impact of adoption on its financial statements.

White Mountains Insurance Group, Ltd. (the “Company” or the “Registrant”) is an exempted Bermuda limited liability company whose principal businesses are conducted through its subsidiaries and other affiliates. The Company’s headquarters is located at 26 Reid Street, Hamilton, Bermuda HM 11, its principal executive office is located at 23 South Main Street, Suite 3B, Hanover, New Hampshire 03755-2053 and its registered office is located at Clarendon House, 2 Church Street, Hamilton, Bermuda HM 11. The Company’s website is www.whitemountains.com. The information contained on the Company’s website is not incorporated by reference into, and is not a part of, this report.

Under GAAP, the Company is required to consolidate any entity in which it holds a controlling financial interest. A controlling financial interest is usually in the form of an investment representing the majority of the subsidiary’s voting interests. However, a controlling financial interest may also arise from a financial interest in a variable interest entity (“VIE”) through arrangements that do not involve ownership of voting interests. The Company consolidates a VIE if it determines that it is the primary beneficiary. The primary beneficiary is defined as the entity that holds a variable interest that gives it both the power to direct the VIE’s activities that most significantly impact its economic performance and the obligation to absorb losses of, or the right to receive returns from, the VIE that could potentially be significant to the VIE. See Note 16 — “Variable Interest Entities.”

The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities as of the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. Actual results could differ from those estimates.

As of December 31, 2025, White Mountains conducted its operations through four reportable segments: (1) Ark/WM Outrigger, (2) HG Global, (3) Kudu and (4) Distinguished, with its remaining operating businesses, holding companies and other assets included in Other Operations. White Mountains has made its segment determination based on consideration of the following criteria: (i) the nature of the business activities of each of the Company’s subsidiaries and affiliates; (ii) the manner in which the Company’s subsidiaries and affiliates are organized; (iii) the existence of primary managers responsible for specific subsidiaries and affiliates; and (iv) the organization of information provided to the Company’s chief operating decision maker (“CODM”) and its Board of Directors. See Note 15 — “Segment Information.”

The Ark/WM Outrigger segment consists of Ark Insurance Holdings Limited and its subsidiaries (collectively, “Ark”) and Outrigger Re Ltd. Segregated Account 2023-1 (“WM Outrigger Re”) (collectively with Ark, “Ark/WM Outrigger”). Ark is a specialty property and casualty insurance and reinsurance company that offers a wide range of niche insurance and reinsurance products, including property, specialty, marine & energy, casualty and accident & health. Ark underwrites select coverages through Lloyd’s Syndicates 4020 and 3902 and Additional Central Settlement Number (“ACSN”) 3832 (collectively, the “Syndicates”) and its wholly-owned subsidiary Group Ark Insurance Limited (“GAIL”). White Mountains acquired a controlling ownership interest in Ark on January 1, 2021 (the “Ark Transaction”). As of December 31, 2025 and 2024, White Mountains owned 72.1% of Ark on a basic shares outstanding basis (61.9% after taking account of management’s equity incentives). The remaining shares are owned by current and former employees of Ark. In the future, management rollover shareholders could earn additional shares in Ark if and to the extent that White Mountains achieves certain thresholds for its multiple of invested capital (“MOIC”) return. If fully earned, these shares would represent an additional 12.3% of the shares outstanding as of December 31, 2025. The liability related to these additional shares is recorded as contingent consideration. Outrigger Re Ltd. is a Bermuda special purpose insurer and segregated accounts company that provides collateralized reinsurance protection on Ark’s Bermuda global property catastrophe excess of loss portfolio. As of December 31, 2025 and 2024, White Mountains owned 100.0% of the preferred equity of its segregated cell, WM Outrigger Re. White Mountains consolidates WM Outrigger Re in its financial statements. See Note 2 — “Significant Transactions.”

The HG Global segment consists of HG Global Ltd. and its wholly-owned subsidiaries (collectively, “HG Global”) and, prior to its deconsolidation on July 1, 2024, the consolidated results of Build America Mutual Assurance Company (“BAM”). See Note 2 — “Significant Transactions.” HG Global was established to fund the startup of BAM and, through its reinsurance subsidiary, HG Re Ltd. (“HG Re”), to provide first-loss reinsurance protection of up to 15%-of-par outstanding for each policy assumed from BAM. HG Global, together with its subsidiaries, funded the initial capitalization of BAM through the purchase of $503.0 million of surplus notes issued by BAM (the “BAM Surplus Notes”). As of December 31, 2025 and 2024, White Mountains owned 96.9% of HG Global’s preferred equity and 88.4% of its common equity.

White Mountains does not have an ownership interest in BAM. However, through June 30, 2024, White Mountains was required to consolidate BAM’s results in its financial statements because BAM is a VIE for which White Mountains was the primary beneficiary. BAM’s results were all attributed to noncontrolling interests. On July 1, 2024, HG Re and BAM amended the terms of the first-loss reinsurance treaty (“FLRT”) with respect to certain governance rights held by HG Re. As a result, and in combination with other governance changes at BAM, White Mountains concluded that it no longer has the power to direct BAM’s activities that most significantly impact its economic performance and is no longer BAM’s primary beneficiary. Accordingly, effective July 1, 2024, White Mountains no longer consolidates BAM. Through June 30, 2024, BAM’s results of operations were presented within the HG Global segment. See Note 2 — “Significant Transactions.”

The Kudu segment consists of Kudu Investment Management, LLC and its subsidiaries (collectively, “Kudu”). Kudu provides capital solutions for boutique asset and wealth managers for a variety of purposes including generational ownership transfers, management buyouts, acquisition and growth finance and legacy partner liquidity. Kudu also provides strategic advice to managers from time to time. Kudu’s capital solutions are generally structured as noncontrolling equity interests in the form of revenue and earnings participation contracts (“Participation Contracts”) and designed to generate immediate cash yields. As of December 31, 2025 and 2024, White Mountains owned 91.2% and 90.4% of Kudu’s basic units outstanding (77.9% and 77.0% on a fully-diluted/fully-converted basis, taking account of management’s equity incentives).

The Distinguished segment consists of WM Phoenix Parent, L.P. and its subsidiaries d/b/a Distinguished Programs (collectively, “Distinguished”). Distinguished is a full-service MGA and program administrator for specialty property and casualty insurance. Distinguished places insurance across a diversified portfolio of programs broadly grouped into two verticals. The ScaleCo vertical consists of established programs, primarily focused on real estate and hospitality end markets. The GrowthCo vertical consists of start-up programs, focused on a diversified set of specialty property and casualty insurance products across multiple industries. On behalf of its insurance carrier partners, Distinguished typically manages all aspects of the placement process, including product development, marketing, underwriting and policy issuance. Distinguished earns commissions based on the volume and profitability of the insurance that it places. Distinguished does not retain insurance risk. On September 2, 2025, White Mountains acquired a controlling financial interest in Distinguished. See Note 2 — “Significant Transactions.” As of December 31, 2025, White Mountains owned 55.5% of Distinguished on a basic units outstanding basis (43.6% on a fully-diluted/fully-converted basis, taking account of management’s equity incentives).

White Mountains’s other operations consist of the Company and its wholly-owned subsidiary, White Mountains Capital, LLC (“WM Capital”), its other intermediate holding companies, its wholly-owned investment management subsidiary, White Mountains Advisors LLC (“WM Advisors”), investment assets managed by WM Advisors, its interests in Bamboo Ide8 Insurance Services LLC (“Bamboo MGA”) and its subsidiaries through a special purpose vehicle (the “Bamboo SPV”), MediaAlpha, Inc. (“MediaAlpha”), DavidShield PassportCard Ltd. and its subsidiaries (collectively, “PassportCard/DavidShield”), BroadStreet Partners, Inc. (“BroadStreet”) through a special purpose vehicle (the “BroadStreet SPV”), Elementum Holdings LP (“Elementum”), White Mountains Partners LLC (“WTM Partners”), Enterprise Electric, LLC d/b/a Enterprise Solutions (“Enterprise Solutions”), two special purpose collateralized reinsurance vehicles that provide reinsurance capacity to Bamboo (the “Bamboo CRVs”), certain other consolidated and unconsolidated entities (“Other Operating Businesses”) and certain other assets (collectively, “Other Operations”).

On December 5, 2025, White Mountains completed the sale of a controlling financial interest in WM Pierce Holdings, Inc. and its subsidiaries, including Bamboo MGA (collectively, the "Bamboo Group"). As a result of the sale, White Mountains deconsolidated the Bamboo Group on December 5, 2025, and Bamboo is no longer a reportable segment. Through December 5, 2025, Bamboo’s results of operations are presented within the Bamboo segment. See Note 2 — “Significant Transactions.” The Bamboo Group’s assets and liabilities have been presented as held for sale as of December 31, 2024. See Note 20 — “Held for Sale.”

Through December 5, 2025, the Bamboo segment consisted of PM Holdings LLC (“Bamboo Holdings”), Bamboo MGA and Ide8 Re, Inc. (the “Bamboo Captive”) (collectively, “Bamboo”). Bamboo is a capital-light, tech- and data-enabled insurance distribution platform providing homeowners’ insurance and related products to the residential property market in California and, beginning in the third quarter of 2025, in Texas. Bamboo operates primarily through Bamboo MGA, its full-service MGA business, where the company manages all aspects of the placement process on behalf of its fronting and reinsurance carrier partners (“Capacity Providers”), including product development, marketing, underwriting, policy issuance and claims oversight, and it earns commissions based on the volume and profitability of the insurance that it places. Bamboo MGA offers both admitted and non-admitted products.

As of December 31, 2025 and 2024, White Mountains’s invested assets consisted of securities and other investments held for general investment purposes. White Mountains’s portfolio of investment securities held for general investment purposes consists of fixed maturity investments, short-term investments, common equity securities, its investment in MediaAlpha and other long-term investments. Short-term investments consist of interest-bearing money market funds, certificates of deposit and other fixed maturity securities, which at the time of purchase, mature or become available for use within one year. Short-term investments are carried at fair value, which approximated amortized or accreted cost as of December 31, 2025 and 2024. Other long-term investments consist primarily of unconsolidated entities, including Kudu’s Participation Contracts, the Bamboo SPV, PassportCard/DavidShield and the BroadStreet SPV, as well as private equity funds and hedge funds, a bank loan fund and Lloyd’s of London (“Lloyd’s”) trust deposits.

White Mountains’s portfolio of fixed maturity investments, including those within short-term investments, are classified as trading securities. Trading securities are reported at fair value as of the balance sheet date. White Mountains’s portfolio of common equity securities, its investment in MediaAlpha and other long-term investments are measured at fair value. White Mountains has generally taken the fair value option for its equity method eligible investments.

Changes in net unrealized investment gains (losses) are reported pre-tax in revenues. Realized investment gains (losses) are accounted for using the specific identification method and are reported pre-tax in revenues. Premiums and discounts on all fixed maturity investments are amortized and accreted to income over the anticipated life of the investment. Income on mortgage and asset-backed securities is recognized using an effective yield based on anticipated prepayments and the estimated economic life of the securities. When actual prepayments differ significantly from anticipated prepayments, the estimated economic life is recalculated, and the remaining unamortized premium or discount is amortized prospectively over the remaining economic life.

Fair value is defined as the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants (an exit price) at a particular measurement date. Fair value measurements are categorized into a hierarchy that distinguishes between inputs based on market data from independent sources (observable inputs) and a reporting entity’s internal assumptions based upon the best information available when external market data is limited or unavailable (unobservable inputs). Quoted prices in active markets for identical assets have the highest priority (“Level 1”), followed by observable inputs other than quoted prices including prices for similar but not identical assets or liabilities (“Level 2”) and unobservable inputs, including the reporting entity’s estimates of the assumptions that market participants would use, having the lowest priority (“Level 3”).

Assets and liabilities carried at fair value include White Mountains’s investment portfolio and derivative instruments. Valuation of assets and liabilities measured at fair value require management to make estimates and apply judgment to matters that may carry a significant degree of uncertainty. In determining its estimates of fair value, White Mountains uses a variety of valuation approaches and inputs. Whenever possible, White Mountains estimates fair value using valuation methods that maximize the use of quoted market prices or other observable inputs. Where appropriate, assets and liabilities measured at fair value have been adjusted for the effect of counterparty credit risk.

Investments valued using Level 1 inputs include White Mountains’s fixed maturity investments, primarily investments in U.S. Treasuries and short-term investments, which include U.S. Treasury Bills, common equity securities and its investment in MediaAlpha. For investments in active markets, White Mountains uses the quoted market prices provided by outside pricing services to determine fair value.

Investments valued using Level 2 inputs include fixed maturity investments which have been disaggregated into classes, including debt securities issued by corporations, municipal obligations, foreign government and agency obligations, mortgage and asset-backed securities and collateralized loan obligations. Investments valued using Level 2 inputs also include certain international listed common equity funds, which White Mountains values using the fund manager’s published net asset value (“NAV”) to account for the difference in market exchange close times, and certain derivative instruments.

In circumstances where quoted market prices are unavailable or are not considered reasonable, White Mountains estimates the fair value using industry standard pricing methodologies and observable inputs such as benchmark yields, reported trades, broker-dealer quotes, issuer spreads, benchmark securities, bids, offers, credit ratings, prepayment speeds, reference data including research publications and other relevant inputs. Given that many fixed maturity investments do not trade on a daily basis, the outside pricing services evaluate a wide range of fixed maturity investments by regularly drawing parallels from recent trades and quotes of comparable securities with similar features. The characteristics used to identify comparable fixed maturity investments vary by asset type and take into account market convention.

White Mountains’s process to assess the reasonableness of the market prices obtained from the outside pricing sources covers substantially all of its fixed maturity investments and includes, but is not limited to, the evaluation of pricing methodologies and a review of the pricing services’ quality control procedures on at least an annual basis, a comparison of invested asset prices obtained from alternate independent pricing vendors on at least a semi-annual basis, monthly analytical reviews of certain prices and a review of the underlying assumptions utilized by the pricing services for select measurements on an ad hoc basis throughout the year. White Mountains also performs back-testing of selected investment sales activity to determine whether there are any significant differences between the market price used to value the security prior to sale and the actual sale price of the security on an ad-hoc basis throughout the year. Prices provided by the pricing services that vary by more than $0.5 million and 5% from the expected price based on these assessment procedures are considered outliers, as are prices that have not changed from period to period and prices that have trended unusually compared to market conditions. In circumstances where the results of White Mountains’s review process does not appear to support the market price provided by the pricing services, White Mountains challenges the vendor provided price. If White Mountains cannot gain satisfactory evidence to support the challenged price, White Mountains will rely upon its own internal pricing methodologies to estimate the fair value of the security in question.

The fair value of debt securities issued by corporations is determined from a pricing evaluation technique that uses information from market sources and integrates relative credit information, observed market movements and sector news. Key inputs include benchmark yields, reported trades, broker-dealer quotes, issuer spreads, two-sided markets, benchmark securities, bids, offers and reference data including sector, coupon, credit quality ratings, duration, credit enhancements, early redemption features and market research publications.

The fair value of municipal obligations is determined from a pricing evaluation technique that uses information from market makers, brokers-dealers, buy-side firms and analysts along with general market information. Key inputs include benchmark yields, reported trades, issuer financial statements, material event notices and new issue data, as well as broker-dealer quotes, issuer spreads, two-sided markets, benchmark securities, bids, offers and reference data including type, coupon, credit quality ratings, duration, credit enhancements, geographic location and market research publications.

The fair value of foreign government and agency obligations is determined from a pricing evaluation technique that uses information from data sources in each respective country, including active market makers and inter-dealer brokers. Key inputs include benchmark yields, reported trades, broker-dealer quotes, issuer spreads, two-sided markets, benchmark securities, bids, offers, local exchange prices, foreign currency exchange rates and reference data including coupon, credit quality ratings, duration and market research publications.

The fair value of mortgage and asset-backed securities and collateralized loan obligations is determined from a pricing evaluation technique that uses information from market sources and leveraging similar securities. Key inputs include benchmark yields, reported trades, underlying tranche cash flow data, collateral performance, plus new issue data, as well as broker-dealer quotes, issuer spreads, two-sided markets, benchmark securities, bids, offers and reference data including issuer, vintage, loan type, collateral attributes, prepayment speeds, default rates, recovery rates, cash flow stress testing, credit quality ratings and market research publications.

Fair value estimates for investments that trade infrequently and have few or no quoted market prices or other observable inputs are classified as Level 3 measurements. Investments valued using Level 3 fair value estimates are based upon unobservable inputs and include investments in certain fixed maturity investments, common equity securities and other long-term investments where quoted market prices or other observable inputs are unavailable or are not considered reliable or reasonable.

Level 3 valuations are generated from techniques that use assumptions not observable in the market. These unobservable inputs reflect White Mountains’s assumptions of what market participants would use in valuing the investment. In certain circumstances, investment securities may start out as Level 3 when they are originally issued, but as observable inputs become available in the market, they may be reclassified to Level 2. Transfers of securities between levels are based on investments held as of the beginning of the period.

As of December 31, 2025, $1,814.4 million of White Mountains’s other long-term investments were classified as Level 3 investments in the GAAP fair value hierarchy, including Kudu’s Participation Contracts, the Bamboo SPV, PassportCard/DavidShield and certain other unconsolidated entities. The determination of the fair value of these securities involves significant management judgment, and the use of valuation analyses and assumptions that are inherently subjective and uncertain.

White Mountains may use a variety of valuation techniques to determine fair value depending on the nature of the investment, including a discounted cash flow analysis, market multiple approach, cost approach and/or liquidation analysis. On an ongoing basis, White Mountains also considers qualitative changes in facts and circumstances, which may impact the valuation of its unconsolidated entities, including economic and market changes in relevant industries, changes to the entity’s capital structure, business strategy and key personnel and any recent transactions. On a quarterly basis, White Mountains evaluates the most recent qualitative and quantitative information of the business and completes a fair valuation analysis for all other long-term investments classified as Level 3 investments. Periodically, and at least on an annual basis, White Mountains uses a third-party valuation firm to complete an independent valuation analysis of significant unconsolidated entities.

As of December 31, 2025, $1,110.4 million of White Mountains’s other long-term investments were measured at fair value using NAV as a practical expedient, including the BroadStreet SPV, private equity funds and hedge funds, a bank loan fund, Lloyd’s trust deposits and insurance-linked securities (“ILS”) funds. Investments for which fair value is measured using NAV as a practical expedient are not classified within the fair value hierarchy.

White Mountains employs a number of procedures to assess the reasonableness of the fair value measurements for other long-term investments measured at NAV, including obtaining and reviewing interim unaudited and annual audited financial statements as well as periodically discussing the valuations and methodologies used to value the underlying investments of each fund with fund managers. However, since fund managers do not provide sufficient information to evaluate the pricing methods and inputs for each underlying investment, White Mountains considers the valuation inputs to be unobservable. The fair value of White Mountains’s other long-term investments measured at NAV are generally determined using the fund manager’s NAV. Certain other long-term investments measured at NAV may be reported to White Mountains on a lag. In these circumstances, the NAV of such investments is adjusted to account for any applicable contributions, distributions, known transactions and/or pricing estimates provided by the fund manager through White Mountains’s reporting date.

Mountains elected the fair value option for the BAM Surplus Notes. White Mountains values the BAM Surplus Notes each quarter using a discounted cash flow analysis. The BAM Surplus Notes are classified as a Level 3 measurement. Upon election of the fair value option, White Mountains made the accounting policy election to present the interest income from the BAM Surplus Notes separately from the change in fair value of the BAM Surplus Notes. See Note 10 — “Municipal Bond Guarantee Reinsurance.”

From time to time, White Mountains holds derivative financial instruments for risk management purposes. White Mountains recognizes all derivatives as either assets or liabilities, measured at fair value, on its consolidated balance sheet. Changes in the fair value of derivative instruments that meet the criteria for hedge accounting are recognized in other comprehensive income (loss) and reclassified into current period pre-tax income (loss) when the hedged items are recognized therein. Changes in the fair value of derivative instruments that do not meet the criteria for hedge accounting are recognized in current period pre-tax income (loss).

Ark accounts for insurance and reinsurance policies that it writes in accordance with ASC 944, Financial Services - Insurance. Ark’s premiums written comprise premiums on insurance contracts incepted during the year as well as premium adjustments related to prior underwriting years. Insurance premiums are recognized as revenues over the loss exposure or coverage period. In most cases, premiums are earned ratably over the term of the contract, with unearned premiums calculated on a monthly pro-rata basis. Catastrophe premiums are earned in proportion to the insurance protection provided. Premiums earned are presented net of amounts ceded to reinsurers. Insurance premiums receivable, representing amounts due from insureds, are presented net of an allowance for uncollectible premiums, including expected credit losses. The allowance is based upon Ark’s ongoing review of amounts outstanding, historical loss data, including delinquencies and write-offs, current and forecasted economic conditions and other relevant factors. Credit risk is partially mitigated by Ark’s ability to cancel the policy if the policyholder does not pay the premium.

Deferred acquisition costs comprise commission and brokerage fees and taxes which are directly attributable to and vary with the production of business. These costs are deferred and amortized to the extent that they relate to successful contract acquisitions over the applicable premium recognition period as acquisition expenses. Deferred acquisition costs are limited to the amount expected to be recovered from future earned premiums and anticipated investment income. A premium deficiency is recognized if the sum of expected loss and loss adjustment expenses (“LAE”), expected dividends to policyholders, unamortized acquisition costs and maintenance costs exceeds related unearned premiums and anticipated investment income. A premium deficiency is recognized by charging any unamortized acquisition costs to expense to the extent required in order to eliminate the deficiency. If the premium deficiency exceeds unamortized acquisition costs, then a liability is accrued for the excess deficiency.

Loss and LAE are charged against income as incurred. Loss and LAE reserves, including estimates for amounts incurred but not reported (“IBNR”), are based on management’s best estimate of the ultimate costs to settle claims, including the effects of inflation and other societal and economic factors. Loss and LAE reserves are presented net of estimated salvage and subrogation recoveries, if applicable. Such estimates are regularly reviewed and updated, and any resulting adjustments are reflected in current results of operations. The process of estimating loss and LAE reserves involves a considerable degree of judgment by management, and the ultimate amount of expense to be incurred could be considerably greater than or less than the amounts currently reflected in the financial statements. See Note 5 — “Loss and Loss Adjustment Expense Reserves.”

As part of its enterprise risk management function, Ark purchases reinsurance for risk mitigation purposes. Ark utilizes reinsurance and retrocessional agreements to reduce earnings volatility, protect capital, limit concentration and accumulation risk and manage within its overall internal risk tolerances and/or those set and agreed by regulators, ratings agencies and Lloyd’s. Ark also enters into reinsurance and retrocessional agreements to reduce its exposures on individual risks and enable it to underwrite policies with higher limits where Ark believes this has a broader business benefit. Ark seeks to protect its downside risk from catastrophes and large loss events by purchasing reinsurance, including excess of loss protections, aggregate covers and industry loss warranties. Ark also considers alternative structures such as collateralized reinsurance, retrocessional reinsurance and catastrophe bonds. The purchase of reinsurance does not discharge Ark from its primary liability for the full value of its policies, and thus the collectability of balances due from Ark’s reinsurers is critical to its financial strength. Ark monitors the financial strength and ratings of its reinsurers on an ongoing basis. See Note 6 — “Third-Party Reinsurance.”

Reinsurance recoverables represent paid loss and LAE, case reserves and IBNR reserves ceded to reinsurers under reinsurance treaties. Amounts recoverable from reinsurers are estimated in a manner consistent with the associated claims liability. Ark reports its reinsurance recoverables net of an allowance for estimated uncollectible reinsurance, including expected credit losses and coverage disputes. The allowance is based upon Ark’s ongoing review of amounts outstanding, length of collection periods, changes in reinsurer credit standing, disputes, applicable coverage defenses and other relevant factors.

The FLRT and all the contracts issued by BAM are accounted for as insurance contracts under ASC 944-605, Financial Guarantee Insurance Contracts. For capital appreciation bonds, par is adjusted to the estimated equivalent par value for current interest paying bonds. Prior to the deconsolidation of BAM, HG Re’s reinsurance balances under the FLRT eliminated in White Mountains’s consolidated financial statements. See Note 10 — “Municipal Bond Guarantee Reinsurance.”

Premiums are generally received upfront and an unearned premium reserve, equal to the amount of the premium received, is established at contract inception. Premiums are recognized in revenue over the period of the contracts in proportion to the amount of insurance protection provided using a constant rate. The constant rate is calculated based on the relationship between the par outstanding in a given reporting period compared with the sum of each of the par amounts outstanding for all periods.

HG Re’s deferred acquisition costs represent the ceding commission paid to BAM. These costs are deferred and amortized to the extent that they relate to successful contract acquisitions over the applicable premium recognition period as acquisition expenses. Deferred acquisition costs are limited to the amount expected to be recovered from future earned premiums and anticipated investment income. A premium deficiency is recognized if the sum of expected loss and LAE, expected dividends to policyholders, unamortized acquisition costs and maintenance costs exceeds related unearned premiums and anticipated investment income. A premium deficiency is recognized by charging any unamortized acquisition costs to expense to the extent required in order to eliminate the deficiency. If the premium deficiency exceeds unamortized acquisition costs, then a liability is accrued for the excess deficiency.

HG Re is party to an excess of loss reinsurance agreement (the “XOLT”) with BAM. The XOLT is accounted for using deposit accounting as the agreement does not meet the risk transfer requirements necessary to be accounted for as reinsurance. Accordingly, any financing revenues related to the XOLT are recorded in other revenues. See Note 10 — “Municipal Bond Guarantee Reinsurance.”

Kudu’s revenues are primarily generated from Participation Contracts, which are generally noncontrolling equity interests in revenue and earnings participation contracts with asset and wealth management firms. Kudu’s Participation Contracts are measured at fair value with the change therein recognized within net realized and unrealized investment gains (losses). Distributions from Kudu’s managers are recognized through investment income when Kudu’s right to receive payment has been established and can be reliably measured, which generally occurs on a quarterly basis in accordance with the terms of the Participation Contracts.

Bamboo’s revenues consist primarily of commission and fee revenues for placement of insurance policies. Commission and fee revenues are measured based on the contractual rates with insurance carriers, net of any amounts expected to be uncollectible and any amounts associated with expected policy cancellations and adjustments, and are recognized when contractual performance obligations have been fulfilled. Bamboo’s primary contractual performance obligations are generally satisfied upon the issuance of an insurance policy. Bamboo’s premiums, commissions and fees receivable consist of insurance premiums and fees receivable from customers and commissions receivable from insurance carriers, net of a provision for amounts estimated to be uncollectible and any amounts associated with expected policy cancellations and adjustments.

Distinguished’s revenues consist primarily of commission and fee revenues related to its placement of insurance policies. Commission revenues are measured based on the contractual rates with its insurance carriers, net of any amounts expected to be uncollectible and any amounts associated with expected policy cancellations and adjustments, and are recognized when contractual performance obligations have been fulfilled. Distinguished also earns fee revenues, primarily related to risk management services provided to certain insureds, which are recognized when contractual performance obligations have been fulfilled. Distinguished’s primary contractual performance obligations are generally satisfied upon the issuance of an insurance policy. Distinguished’s premiums, commissions and fees receivable consist of insurance premiums and fees receivable from insureds and commissions receivable from insurance carriers, net of a provision for amounts estimated to be uncollectible and any amounts associated with expected policy cancellations and adjustments. Premiums receivable are collected on behalf of Distinguished’s insurance carriers. Distinguished’s premiums and commissions payable consist of insurance premiums payable to insurance carriers and commissions payable to sub-agents and brokers.

Other Operations recognizes commissions and fee revenues as well as other revenues when it has satisfied its performance obligations. Enterprise Solutions’s revenues consist primarily of construction revenues from specialty electrical contracting services provided to commercial and institutional customers. Enterprise Solutions’s billings are generally based on contractual terms and may not coincide with its progress in a project. Construction revenues, which are presented within other revenues, are recognized over time using the cost-to-cost percentage of completion input method, based on the ratio of contract costs incurred to date compared to total estimated contract costs. Contract costs incurred to date and expected total contract costs are continuously monitored during the term of the contract. Enterprise Solutions records accounts receivable, which are presented within other assets, for amounts billed to the customer, net of a provision for amounts estimated to be uncollectible. If the recognized revenue is greater than the amount billed to the customer, a contract asset is recorded within other assets. Contract assets also include amounts billed under retainage provisions that cannot be collected until the contract work has been completed and approved. If the amount billed to the customer is greater than the recognized revenue, a contract liability is recorded within other liabilities.

White Mountains’s Long-Term Incentive Plan (the “WTM Incentive Plan”) provides for grants of various types of share-based and non-share-based incentive awards to key employees of White Mountains. Non-share-based awards are recognized over the related service periods based on management’s best estimate of the amounts at which the awards are expected to be paid. Share-based compensation which is typically settled in cash, such as performance shares, is classified as a liability-type award. The compensation cost for liability-classified awards is measured initially at the grant date fair value and remeasured each reporting period until settlement. The compensation cost for equity-classified awards expected to be settled in shares, such as restricted shares, is measured at the original grant date fair value of the award. The compensation cost for all awards is recognized for the vested portion of the awards over the related service periods. See Note 12 — “Employee Share-Based Incentive Compensation Plans.”

White Mountains has subsidiaries and branches that operate in various jurisdictions around the world and are subject to tax in the jurisdictions in which they operate. As of December 31, 2025, the primary jurisdictions in which the Company’s subsidiaries and branches operate and were subject to tax include Israel, Luxembourg, the United Kingdom and the United States. Income earned or losses generated by companies outside the United States are generally subject to an overall effective tax rate lower than that imposed by the United States.

Deferred tax assets and liabilities are recorded when a difference between the carrying amounts of assets and liabilities for financial reporting purposes and the amounts for tax purposes exists, or there are other temporary differences. The deferred tax asset or liability is recorded based on tax rates expected to be in effect when the difference reverses. Deferred tax assets represent amounts available to reduce income taxes payable in future periods. White Mountains records a valuation allowance against deferred tax assets if it becomes more likely than not that all or a portion of a deferred tax asset will not be realized. Changes in valuation allowances from period to period are included in income tax expense in the period of change. See Note 8 — “Income Taxes.”

White Mountains has entered into lease agreements, primarily for office space and equipment. These leases are classified as operating leases, with lease expense recognized on a straight-line basis over the term of the lease. Lease assets and liabilities are not recorded for leases with a term at inception of one year or less. Lease incentives, such as free rent or landlord reimbursements for leasehold improvements, are recognized at lease inception and amortized on a straight-line basis over the term of the lease. Lease expense and the amortization of leasehold improvements are recognized within general and administrative expenses. Lease payments related to options to extend or renew the lease term are excluded from the calculation of lease liabilities unless White Mountains is reasonably certain of exercising those options.

Noncontrolling interests consist of the ownership interests of noncontrolling shareholders in consolidated entities. White Mountains has both redeemable and nonredeemable noncontrolling interests. Noncontrolling interests with redemption features that are not within White Mountains’s control are classified as redeemable noncontrolling interests, which are considered temporary equity and presented as mezzanine equity on the balance sheet. Redeemable noncontrolling interests are excluded from White Mountains’s total equity. The redeemable noncontrolling interests relate to Distinguished. Noncontrolling interests that do not have any redemption features are classified as nonredeemable noncontrolling interests, which are considered permanent equity and included in White Mountains’s total equity on the balance sheet. Nonredeemable noncontrolling interests are presented separately from White Mountains’s common shareholders’ equity. See Note 13 — “Common Shareholders’ Equity and Noncontrolling Interests.”

Comprehensive income (loss) is attributable to both redeemable and nonredeemable noncontrolling interests and is presented net of related income taxes in the statements of operations and comprehensive income (loss). In addition, White Mountains recognizes an adjustment to the carrying value of the redeemable noncontrolling interests to the extent that the carrying value is below the redemption value. The adjustment for redeemable noncontrolling interests is recognized through White Mountains’s common shareholders’ equity. When calculating basic and diluted earnings per share, the adjustment for redeemable noncontrolling interests is treated as being akin to a dividend and presented as an adjustment to net income (loss) attributable to White Mountains’s common shareholders.

Fair value measurements are categorized into a hierarchy that distinguishes between inputs based on market data from independent sources (observable inputs) and a reporting entity’s internal assumptions based upon the best information available when external market data is limited or unavailable (unobservable inputs). Quoted prices in active markets for identical assets or liabilities have the highest priority (Level 1), followed by observable inputs other than quoted prices, including prices for similar but not identical assets or liabilities (Level 2) and unobservable inputs, including the reporting entity’s estimates of the assumptions that market participants would use, having the lowest priority (Level 3). See Note 18 — “Fair Value of Financial Instruments.”

White Mountains accounts for purchases of businesses using the acquisition method, which requires the measurement of assets acquired, including other intangible assets, liabilities assumed, including contingent consideration liabilities, and any noncontrolling interests in the acquired entities at their estimated fair values as of the acquisition date. The acquisition date fair values represent management’s best estimates and are based upon established valuation techniques, reasonable assumptions and, where appropriate, valuations performed by independent third parties. In circumstances where additional information is required in order to determine the acquisition date fair value of balance sheet amounts, provisional amounts may be recorded as of the acquisition date and may be subject to subsequent adjustment throughout the measurement period, which is up to one year from the acquisition date. Measurement period adjustments are recognized in the period in which they are determined. The results of operations and cash flows of businesses acquired are included in the consolidated financial statements from the acquisition date. White Mountains accounts for purchases of other intangible assets that do not meet the definition of a business as asset acquisitions. Asset acquisitions are recognized at the amount of consideration paid, which is deemed to equal fair value.

Other intangible assets consist primarily of underwriting capacity, agency relationships, customer relationships and trade names. The acquisition date fair values of other intangible assets are estimated using income approach techniques, which use future expected cash flows to develop a discounted present value amount. The multi-period-excess-earnings method estimates fair value using the present value of the incremental after-tax cash flows attributable solely to the other intangible asset over its remaining life. This approach was used to estimate the fair value of other intangible assets associated with the underwriting capacity, agency relationships and customer relationships. The relief-from-royalty method was used to estimate fair value for other intangible assets that relate to rights that could be obtained via a license from a third-party owner. Under this method, the fair value is estimated using the present value of license fees avoided by owning rather than leasing the asset. This technique was used to estimate the fair value of trade names, patents and certain information technology platforms. The with-or-without method estimates the fair value of other intangible assets that provide an incremental benefit. Under this method, the fair value of the other intangible asset is calculated by comparing the value of the entity with and without the other intangible asset. This approach was used to estimate the fair value of non-compete agreements.

Goodwill and other intangible assets with indefinite lives are not amortized, but rather are evaluated for impairment on an annual basis, or whenever indications of potential impairment exist. In the absence of any indications of potential impairment, the evaluation of goodwill and indefinite-lived intangible assets is performed no later than the interim period in which the anniversary of the acquisition date falls. White Mountains initially evaluates goodwill and indefinite-lived intangible assets using a qualitative approach (step zero) to determine whether it is more likely than not that the implied fair value is greater than the carrying value. If the results of the qualitative evaluation indicate that it is more likely than not that the carrying value of goodwill or the indefinite-lived intangible assets exceeds the implied fair value, White Mountains performs a quantitative analysis to compare the fair value with the carrying value. If the carrying value exceeds the estimated fair value, then an impairment charge is recognized through current period pre-tax income (loss).

Other intangible assets with finite lives are initially measured at their acquisition date fair values and subsequently amortized over their economic lives. Finite-lived intangible assets are presented net of accumulated amortization on the balance sheet. Finite-lived intangible assets are reviewed for impairment when events occur or there are changes in circumstances indicating that their carrying value may exceed fair value. An impairment exists when the carrying value of a finite-lived intangible asset exceeds the fair value. See Note 4 — “Goodwill and Other Intangible Assets.”

The consideration for the Ark Transaction included potential future payments to management rollover shareholders, which are payable in a variable number of shares, if and to the extent that White Mountains achieves certain MOIC return thresholds. This additional consideration is generally payable in three equal tranches at MOIC thresholds of 2.0x, 2.5x and 3.0x. If fully earned, these shares would represent an additional 12.3% of the shares outstanding as of December 31, 2025. The liability related to these additional shares is recorded as contingent consideration. Contingent consideration in a business combination that is classified as a liability is measured at fair value on the acquisition date and remeasured to fair value each subsequent reporting period with changes in the fair value recognized through pre-tax income (loss). As a result of the Ark Transaction, White Mountains recognized a contingent consideration liability of $22.5 million as of January 1, 2021. During the years ended December 31, 2025, 2024 and 2023, White Mountains recognized an expense of $173.0 million, $61.3 million and $48.7 million for the change in the fair value of its contingent consideration liability. As of December 31, 2025 and 2024, White Mountains’s contingent consideration liability was $328.3 million and $155.3 million. The contingent consideration liability is a Level 3 measurement.

White Mountains adopted ASU 2023-09, Income Taxes (Topic 740): Improvements to Income Tax Disclosures (“ASU 2023-09”) effective for its annual disclosures for the year ended December 31, 2025. ASU 2023-09 requires disclosure of disaggregated information about a reporting entity’s effective tax rate reconciliation as well as information on income taxes paid. ASU 2023-09 was adopted retrospectively, including the recasting of previously reported income tax information. See Note 8 — “Income Taxes.”

In November 2024, the FASB issued ASU 2024-03, Income Statement—Reporting Comprehensive Income—Expense Disaggregation Disclosures (Subtopic 220-40): Disaggregation of Income Statement Expenses (“ASU 2024-03”), which requires additional disclosure of the nature of expenses included in the income statement. ASU 2024-03 requires disclosures about specific types of expenses (i.e., (a) purchases of inventory, (b) employee compensation, (c) depreciation and (d) intangible asset amortization) included in the expense captions presented on the face of the income statement as well as disclosures about selling expenses. ASU 2024-03 does not change the requirements for the presentation of expenses on the income statement. ASU 2024-03 is effective for annual reporting periods beginning after December 15, 2026 and interim reporting periods beginning after December 15, 2027. Early adoption is permitted. Although ASU 2024-03 requires comparative disclosures for all periods presented, reporting entities will be permitted to begin applying the guidance prospectively with the option for retrospective application for all prior periods presented. Accordingly, the new disclosure requirements in ASU 2024-03 are initially required within White Mountains’s Annual Report on Form 10-K for the year ending December 31, 2027. White Mountains is in the process of evaluating the potential impact of adoption on its financial statements.