Exhibit 99.1 CONTACT: Rob Seelig (603) 640-2212 WHITE MOUNTAINS REPORTS FOURTH QUARTER RESULTS HAMILTON, Bermuda (February 6, 2026) - White Mountains Insurance Group, Ltd. (NYSE: WTM) reported book value per share of $2,188 as of December 31, 2025, an increase of 18% for the fourth quarter of 2025 and 25% for the year ended December 31, 2025, including dividends. Liam Caffrey, CEO, commented, "We had an excellent year, with BVPS growth of 18% in the quarter and 25% for the year. The largest contributor in b ...