White Mountains Insurance Group, Ltd.
White Mountains Insurance Group, Ltd. (WTM) Stock Ownership
Institutional vs insider vs public ownership from 13F and float data — top holders, activity, and insider trades below.
SEC 13F · FMP · WTM · as of Sep 30, 2025
Ownership Breakdown
338
Institutional Holders
▲ 12 vs Q2
$3.89B
Total Inst. Value
▼ $275.15M vs Q2
2.48M
Shares Outstanding
freeFloat 95.54%
2.33M
13F Shares Held
▲ 6,359 vs Q2
Institutional ownership = 13F shares ÷ total outstanding. Insider % = 100 − free float. Public % = free float − institution %. Data: FMP /symbol-positions-summary + /shares-float + SEC EDGAR.
Top Institutional Holders
WTM largest shareholders · institutional ownership
Q3 2025 · SEC 13F
Showing top 10 holders
| Holder | Shares | % Owned | Weight | Value | Reported | Change |
|---|---|---|---|---|---|---|
VANGUARD GROUP INC fire, marine & casualty insurance | 247.0K | 9.72% | 9.72% | $412.87B | Nov 7, 2025 | ▼ 2.2K |
DIMENSIONAL FUND ADVISORS LP fire, marine & casualty insurance | 157.2K | 6.19% | 6.19% | $262.79B | Nov 12, 2025 | ▲ 1.5K |
MORGAN STANLEY fire, marine & casualty insurance | 138.9K | 5.46% | 5.46% | $232.11B | May 27, 2026 | ▼ 26.2K |
NEUBERGER BERMAN GROUP LLC fire, marine & casualty insurance | 115.0K | 4.53% | 4.53% | $192.25B | Nov 12, 2025 | ▲ 31.3K |
BLACKROCK, INC. fire, marine & casualty insurance | 112.6K | 4.43% | 4.43% | $188.18B | Nov 12, 2025 | ▼ 579 |
RIVER ROAD ASSET MANAGEMENT, LLC fire, marine & casualty insurance | 109.6K | 4.31% | 4.31% | $183.18B | Nov 12, 2025 | ▼ 304 |
FULLER & THALER ASSET MANAGEMENT, INC. fire, marine & casualty insurance | 108.1K | 4.25% | 4.25% | $180.68B | Nov 13, 2025 | ▲ 7.1K |
COOKE & BIELER LP fire, marine & casualty insurance | 107.9K | 4.24% | 4.24% | $180.28B | Oct 31, 2025 | ▲ 31.1K |
FIDUCIARY MANAGEMENT INC /WI/ fire, marine & casualty insurance | 94.4K | 3.71% | 3.71% | $157.76B | Nov 14, 2025 | ▲ 22.9K |
BOSTON PARTNERS fire, marine & casualty insurance | 84.4K | 3.32% | 3.32% | $142.52B | Nov 13, 2025 | ▼ 4.9K |
Data from SEC Form 13F filings. Ownership bar normalised to largest holder. Change flags: isNew / isSoldOut / changeInSharesNumber (FMP extract-analytics/holder).
Institutional Activity
Q3 2025 vs prior quarter
Q3 2025
23
Increased
+140.3K shares0
New Positions
first time holders27
Decreased
−79.3K shares0
Sold Out
fully exitedNet shares change (top 50)
+61.0K
+140.3K / −79.3K
Net new holders
-4
0 new / 0 exited
Based on top 50 institutional holders by position size. Fields: isNew, isSoldOut, changeInSharesNumber (FMP extract-analytics/holder, limit=50).
Insider Buying vs Selling
WTM insider trading · insider activity
Source: SEC Form 4
9
Buy transactions
0
Sell transactions
0.00
Buy/Sell ratio
$0M
Total disposed
Recent Insider Transactions
Showing 10 most recent · Common Stock only
| Name · Role | Date | Type | Shares | Price | Value | After Trans. | Filing |
|---|---|---|---|---|---|---|---|
Tanner David Allen director | May 21, 2026 | Award | 135 | — | — | 2.0K | Form 4 ↗ |
SHANK SUZANNE F. director | May 21, 2026 | Award | 135 | — | — | 1.0K | Form 4 ↗ |
Hicks Weston M director | May 21, 2026 | Award | 190 | — | — | 2.9K | Form 4 ↗ |
Gelston Philip A director | May 21, 2026 | Award | 135 | — | — | 1.7K | Form 4 ↗ |
Dillon Margaret director | May 21, 2026 | Award | 135 | — | — | 1.1K | Form 4 ↗ |
Chu John director | May 21, 2026 | Award | 135 | — | — | 335 | Form 4 ↗ |
CHOKSI MARY C director | May 21, 2026 | Award | 135 | — | — | 2.0K | Form 4 ↗ |
Carlson Peter M director | May 21, 2026 | Award | 135 | — | — | 852 | Form 4 ↗ |
CAMPBELL REID TARLTON director | May 21, 2026 | Award | 135 | — | — | 10.6K | Form 4 ↗ |
SEELIG ROBERT LAWRENCE EVP & General Counsel | Mar 19, 2026 | Gift | 50 | — | — | 17.9K | Form 4 ↗ |
Source: /insider-trading/search (FMP stable). Buy/Sell direction: acquisitionOrDisposition A=Buy, D=Sell. RSU vesting (M-Exempt) excluded from sentiment bar. All data from SEC EDGAR public filings.
About institutional & insider ownership
White Mountains Insurance Group, Ltd. (WTM) is primarily owned by institutional investors, who hold approximately 94.0% of total shares outstanding. Company insiders own approximately 4.46%, while retail and public investors account for the remaining 1.53%.
The largest institutional shareholder of White Mountains Insurance Group, Ltd. is VANGUARD GROUP INC, holding approximately 247,004 shares — equal to 9.72% of outstanding shares — as of September 30, 2025.
A total of 338 institutional investors currently hold WTM stock, with a combined institutional value of approximately $3.89 billion as of the most recent 13F filing period.
Frequently asked questions
WTM ownershipWhite Mountains Insurance Group, Ltd. (WTM) is primarily owned by institutional investors, who hold approximately 94.0% of shares. The largest shareholder is VANGUARD GROUP INC with a 9.72% stake. Company insiders hold 4.46%. Data sourced from SEC Form 13F as of September 30, 2025.