White Mountains Insurance Group, Ltd.
Ownership
Ownership Structure
Who owns White Mountains Insurance Group, Ltd. (WTM)? This page shows the largest institutions and funds, the ownership structure and the latest insider transactions. 95.4% of the shares are freely tradable; institutional investors hold 94.0%.
Largest Shareholders
Institutions
| Name | Stake (%) | Shares | Change (%) | Date |
|---|---|---|---|---|
| Dimensional Fund Advisors, Inc. | 6.66 | 158,954 | +1.5 | 06/30/2026 |
| Neuberger Berman Group LLC | 5.23 | 124,715 | -3.8 | 03/31/2026 |
| River Road Asset Management, LLC | 4.86 | 115,880 | -3.8 | 06/30/2026 |
| Vanguard Portfolio Management, LLC | 4.84 | 115,553 | +0.0 | 03/31/2026 |
| BlackRock Inc | 4.75 | 113,328 | +0.9 | 03/31/2026 |
| Vanguard Capital Management, LLC | 4.57 | 109,157 | +0.0 | 03/31/2026 |
| Fuller & Thaler Asset Management Inc | 4.38 | 104,561 | -51.7 | 03/31/2026 |
| Cooke & Bieler LP | 3.57 | 85,120 | -18.8 | 06/30/2026 |
Funds
| Name | Stake (%) | Shares | Change (%) | Date |
|---|---|---|---|---|
| FullerThaler Beh Small-Cap Value SMA | 3.69 | 88,037 | +4,196.6 | 06/30/2026 |
| FullerThaler Behavioral Small-Cap Value | 3.69 | 88,037 | -3.5 | 06/30/2026 |
Largest reported positions according to regulatory filings; stake as a percentage of shares outstanding, change versus the previous filing. Source: fundamentals data.
Insider holdings
| Person | Role | Shares | Value | As of | Type |
|---|---|---|---|---|---|
| Tanner David Allen | Director | 2,012 | 4,141,300 $ | Aug 31, 2026 | direct |
| Klar Stephen | Director | 113 | 232,588 $ | Aug 26, 2026 | direct |
Holdings as of each person's most recent SEC Form 4 filing — excluding options and RSUs, which are not shares yet. Holdings may have changed between two filings.
Insiders
Insider Transactions
| Date | Person | Role | Type | Shares | Price | Value |
|---|---|---|---|---|---|---|
| Aug 31, 2026 | Tanner David Allen | Director | Other | 2 | 0.00 | – |
| Aug 26, 2026 | Klar Stephen | Director | Other | 113 | 0.00 | – |
Reportable transactions by officers and major shareholders from SEC Form 4 filings. "Other" includes things like stock grants and option exercises without a buy/sell character. View all insider transactions →
Data as of: September 17, 2026 · Source: fundamental data & SEC filings (annual and quarterly reports, 10-K/10-Q)
Note: pure fact-based analysis, not investment advice and not a solicitation to buy or sell. All figures without guarantee.