WHITE MOUNTAINS INSURANCE GROUP LTD

This Proxy Statement is being furnished in connection with the solicitation of proxies on behalf of the Company’s Board of Directors (the “Board”) for the 2025 Annual General Meeting of Members (the “2025 Annual Meeting”), to be held on Thursday, May 22, 2025 at 8:00 am Atlantic Time at Rosewood Bermuda Hotel, 60 Tucker’s Point Drive, Hamilton Parish, Bermuda.

Holders of the Company’s common shares, par value $1.00 per share, as of the close of business on Monday, March 31, 2025, the record date, are entitled to vote at the meeting. The solicitation of proxies will be made primarily by mail, and the Proxy Statement and related proxy materials will be sent to registered shareholders on or about April 17, 2025.

You can ensure that your common shares are properly voted at the meeting by completing, signing, dating and returning the enclosed proxy card in the envelope provided. Shareholders may also vote their shares by telephone or via the internet in accordance with the instructions on your proxy card. Shareholders have the right to appoint another person (who need not be a shareholder) to represent the shareholder at the meeting by completing an alternative form of proxy which can be obtained from the Corporate Secretary or by notifying the Inspectors of Election (see page 70). Every shareholder entitled to vote has the right to do so either in person or by one or more persons authorized by a written proxy executed by such shareholder and filed with the Corporate Secretary. Any proxy duly executed will continue in full force and effect unless revoked by the person executing it in writing or by the filing of a subsequent proxy.

Sending in a signed proxy will not affect your right to attend the meeting and vote. If a shareholder attends the meeting and votes in person, his or her signed proxy is considered revoked.

IMPORTANT VOTING INFORMATION

If you hold your shares through a broker, bank or other financial institution, in order for your vote to be counted on any matter other than Proposal 4 (the ratification of the appointment of PwC as the Company’s independent registered public accounting firm for 2025), you must provide specific voting instructions to your broker, bank or financial institution by completing and returning the proxy card or following the instructions provided to you to vote your shares via telephone or the internet. Voting deadlines vary by institution. Please check with your broker, bank or other financial institution for the voting cut-off date for WTM.

Your Participation in Voting the Shares You Own Is Important

Voting your shares is important to ensure that you have a say in the governance of your company. Please review the proxy materials and follow the instructions on the proxy card to vote your shares. We hope you will exercise your rights and fully participate in your Company’s future.

More Information Is Available

If you have any questions about this rule or the proxy voting process in general, please contact the broker, bank or other financial institution where you hold your shares. The U.S. Securities and Exchange Commission (“SEC”) has information available on the internet at: https://www.investor.gov/shareholder-voting with more information about your voting rights as a shareholder.