WHITE MOUNTAINS INSURANCE GROUP LTD

**UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

SCHEDULE 14A

Proxy Statement Pursuant to Section 14(a) of

the Securities Exchange Act of 1934 (Amendment No. )

WHITE MOUNTAINS INSURANCE GROUP, LTD.

(Name of Registrant as Specified In Its Charter)

Notice of 2026

Annual General Meeting

Of Members and

Proxy Statement

LETTER FROM THE BOARD OF DIRECTORS

FROM OUR BOARD OF DIRECTORS

Dear Fellow Shareholders:

As your Board of Directors, we oversee White Mountains’s efforts to create superior growth in intrinsic value per share over long periods of time. Your Company seeks to achieve this goal by making opportunistic and value-oriented acquisitions of businesses primarily in the insurance, financial services and related sectors, operating these businesses and, if and when attractive exit valuations become available, disposing of these businesses. Since the Company’s IPO in 1985, we have delivered annualized growth in book value per share of 13% and market value per share of 12%.

2025 was an excellent year for your Company. We finished 2025 with book value per share of $2,188, up 25% for the year. The successful sale of Bamboo in December was the biggest driver, adding roughly $320 to book value per share. Total shareholder return was 7% in 2025, compared to 18% for the S&P 500 and 10% for the S&P 500 P&C Insurance Index.

Apart from Bamboo, our operating businesses generally produced solid to very good results in 2025. Ark produced excellent results while growing premiums 16%. Kudu had a good year, producing a 13% return on equity and closing three acquisitions during the year. HG Global generated premiums of $61 million, driven by strong activity in the primary and secondary markets.

Your Company also added value through capital deployment and capital management activities. During the year, we acquired a majority stake in Distinguished Programs, an MGA and program administrator for specialty property & casualty insurance, and made a strategic investment in BroadStreet Partners, a top-10 North American insurance brokerage. In April, White Mountains Partners completed its acquisition of Enterprise Solutions, a leading provider of specialty electrical contracting services. And, over the year, we repurchased roughly $200 million of shares, inclusive of our self-tender offer, at accretive prices.

The Board takes its role in the planning of thoughtful, orderly succession seriously, and we were delighted to announce Liam Caffrey’s promotion to CEO and appointment as a fellow Director effective January 1 st. Mr. Caffrey is a proven executive who brings deep insurance experience to his new role, and we are confident that owners will prosper under his leadership. We also congratulated our outgoing CEO, Manning Rountree, on his well-deserved retirement after an impactful 21-year career at White Mountains. The Company flourished during his tenure as CEO, and he left it well-positioned for the future. We are pleased that Mr. Rountree will remain employed as a Senior Advisor through January 1, 2028.

Ongoing Dialogue with Shareholders Through Proactive Engagement

Over the last year, members of the Board and management reached out to shareholders owning 75% of White Mountains’s shares outstanding and met with all shareholders--owning 31% of shares outstanding--who accepted a meeting. In years past, feedback from these shareholder discussions has informed changes to our executive compensation program and enhanced disclosures about the skills and areas of expertise of our Board, as well as improvements to our ESG, risk management and human capital management practices. This year, these shareholder discussions focused primarily on our business performance and outlook, approach to capital management, CEO and CFO succession, board composition and refreshment, compensation philosophy and corporate governance practices. Shareholders were supportive and provided valuable feedback.

Our core principles served us well in 2025 and will continue to guide us going forward. It is a privilege to serve as your Board, and we value highly your support of White Mountains.

Sincerely,

The White Mountains Insurance Group Board of Directors

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 affiliates. Within this report, the term “White Mountains” is used to refer to one or more entities within the consolidated organization, as the context requires.

White Mountains is engaged in the business of making opportunistic and value-oriented acquisitions of businesses and assets in the insurance, financial services and related sectors, operating these businesses and assets through its subsidiaries and, if and when attractive exit valuations become available, disposing of these businesses and assets.

As of December 31, 2025, White Mountains conducted its business primarily in five areas: property and casualty insurance and reinsurance, municipal bond guarantee reinsurance, capital solutions for asset and wealth management firms, specialty insurance distribution and other operations. White Mountains’s property and casualty insurance and reinsurance business is conducted through its subsidiary 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”). White Mountains’s municipal bond guarantee reinsurance business is conducted through its subsidiary HG Global Ltd. and its reinsurance subsidiary HG Re Ltd. (“HG Re”) (collectively with HG Re, “HG Global”). White Mountains provides capital solutions for asset and wealth management firms through its subsidiary Kudu Investment Management, LLC and its subsidiaries (collectively, “Kudu”). White Mountains’s specialty insurance distribution business is conducted through its subsidiary WM Phoenix Parent, L.P. and its subsidiaries d/b/a Distinguished Programs (collectively, “Distinguished”). 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 (collectively, “Bamboo”) 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”). As of December 31, 2025, White Mountains’s reportable segments were Ark/WM Outrigger, HG Global, Kudu and Distinguished, with its remaining operating businesses, holding companies and other assets included in Other Operations.

The 2026 Annual General Meeting will be confined to a shareholder vote on the proposals set forth in this Proxy Statement and on such other matters properly brought before the meeting.

For a reconciliation of non-GAAP measures used in this Proxy Statement to their most comparable GAAP measures, see Annex A.