SEC Form 4 · Updated Daily
WTM
— WHITE MOUNTAINS INSURANCE GROUP, LTD. OwnershipInsider and institutional ownership derived from SEC Form 4 filings. Click any owner to see their holdings across every company they’ve filed on, and how their position has changed over time.
Current Reporting Owners
| Owner | Role | Shares Owned | As Of | Last Activity |
|---|---|---|---|---|
| BYRNE JOHN JOSEPH | 10%+ Owner | 428,500 | 2013-02-05 | — |
| BERKSHIRE HATHAWAY INC | 10%+ Owner | 89,279 | 2008-10-31 | S |
| BUFFETT WARREN E | 10%+ Owner | 89,279 | 2008-10-31 | S |
| GENERAL REINSURANCE CORP | 10%+ Owner | 89,279 | 2008-10-31 | S |
| GENERAL RE CORP | 10%+ Owner | 89,279 | 2008-10-31 | S |
| SEELIG ROBERT LAWRENCE | Officer | 17,857 | 2026-03-19 | G |
| Rountree George Manning | Director · Officer | 13,809 | 2025-12-19 | S |
| CAMPBELL REID TARLTON | Director | 10,575 | 2026-05-21 | A |
| COCHRAN ROBERT PHILLIPS | Director | 8,045 | 2011-05-26 | A |
| DAVIS MORGAN W | Director | 6,709 | 2022-12-28 | G |
| FASS STEVE ELLIOTT | Director | 5,535 | 2007-02-25 | F |
| Linker David | Officer | 4,725 | 2017-03-01 | A |
| Brouillette Yves | Director | 4,121 | 2019-05-23 | A |
| WATERS ALLAN LEWIS | Director | 3,735 | 2015-02-25 | A |
| Caffrey Liam P | Officer | 3,650 | 2026-02-25 | A |
| Bazos Frank R | Officer | 3,600 | 2020-02-27 | A |
| Hicks Weston M | Director | 2,936 | 2026-05-21 | A |
| HOLIDAY EDITH E | Director | 2,827 | 2020-05-21 | A |
| GILLESPIE JOHN DAVIES | Director | 2,825 | 2013-05-23 | A |
| Harrison Giles E | Officer | 2,675 | 2026-02-25 | A |
| Oberting Kernan V | Officer | 2,134 | 2016-01-01 | F |
| Tanner David Allen | Director | 2,012 | 2026-08-31 | G |
| CHOKSI MARY C | Director | 1,993 | 2026-05-21 | A |
| Hildreth Michaela | Officer | 1,825 | 2026-02-25 | A |
| Tolman Gary Charles | Officer | 1,822 | 2018-05-24 | A |
| Gelston Philip A | Director | 1,703 | 2026-05-21 | A |
| PALMER JESS BRIAN | Officer | 1,703 | 2021-01-01 | F |
| CHOKEL CHARLES BERGEN | Officer | 1,600 | 2008-02-27 | A |
| GILLESPIE GEORGE JOSEPH III | Director | 1,400 | 2010-05-26 | A |
| Papamichael Michael A | Officer | 1,200 | 2026-02-25 | A |
| CLARK HOWARD LONGSTRETH JR | Director | 1,170 | 2013-05-23 | A |
| SMITH LOWNDES ANDREW | Director | 1,102 | 2019-12-10 | S |
| Dillon Margaret | Director | 1,080 | 2026-05-21 | A |
| SHANK SUZANNE F. | Director | 1,006 | 2026-05-21 | A |
| Carlson Peter M | Director | 852 | 2026-05-21 | A |
| Yi Steven | Director | 525 | 2025-05-22 | A |
| Chu John | Director | 335 | 2026-05-21 | A |
| BERKOWITZ BRUCE R | Director | 300 | 2009-06-08 | A |
| Klar Stephen | Director | 113 | 2026-08-26 | A |
| Frinquelli Angelo Michael | Director | 0 | 2017-11-20 | S |
| FOY DAVID THOMAS | Officer | 0 | 2017-05-24 | F |
| BARRETTE RAYMOND JOSEPH RENE | Director · Officer | 0 | 2017-03-01 | D |
| HUTTON TOM | Officer | 0 | 2006-02-06 | — |
Recent Filings
| Date | Owner | Activity | Shares | Price | Owned After |
|---|---|---|---|---|---|
| 2026-08-31 | Tanner David Allen | Gift | 2 | $0.00 | 2,012 |
| 2026-08-26 | Klar Stephen | — | — | — | 0 |
| 2026-08-26 | Klar Stephen | Grant / award | 113 | $0.00 | 113 |
| 2026-05-21 | Chu John | — | — | — | 200 |
| 2026-05-21 | CAMPBELL REID TARLTON | Grant / award | 135 | $0.00 | 10,575 |
| 2026-05-21 | Carlson Peter M | Grant / award | 135 | $0.00 | 852 |
| 2026-05-21 | CHOKSI MARY C | Grant / award | 135 | $0.00 | 1,993 |
| 2026-05-21 | Chu John | Grant / award | 135 | $0.00 | 335 |
| 2026-05-21 | Dillon Margaret | Grant / award | 135 | $0.00 | 1,080 |
| 2026-05-21 | Gelston Philip A | Grant / award | 135 | $0.00 | 1,703 |
| 2026-05-21 | Hicks Weston M | Grant / award | 190 | $0.00 | 2,936 |
| 2026-05-21 | SHANK SUZANNE F. | Grant / award | 135 | $0.00 | 1,006 |
| 2026-05-21 | Tanner David Allen | Grant / award | 135 | $0.00 | 2,014 |
| 2026-03-19 | SEELIG ROBERT LAWRENCE | Gift | 50 | $0.00 | 17,857 |
| 2026-03-04 | Tanner David Allen | Gift | 225 | $0.00 | 1,879 |
| 2026-02-25 | SEELIG ROBERT LAWRENCE | Grant / award | 775 | $0.00 | 2,500 |
| 2026-02-25 | Papamichael Michael A | Grant / award | 500 | $0.00 | 1,200 |
| 2026-02-25 | Hildreth Michaela | Grant / award | 600 | $0.00 | 1,825 |
| 2026-02-25 | Harrison Giles E | Grant / award | 775 | $0.00 | 2,675 |
| 2026-02-25 | Caffrey Liam P | Grant / award | 1,500 | $0.00 | 3,650 |
| 2026-01-01 | Papamichael Michael A | — | — | — | 12 |
| 2026-01-01 | Papamichael Michael A | — | — | — | 1,100 |
| 2026-01-01 | Papamichael Michael A | — | — | — | 503 |
| 2026-01-01 | Caffrey Liam P | Tax withholding | 425 | $2078.03 | 1,655 |
| 2026-01-01 | SEELIG ROBERT LAWRENCE | Tax withholding | 398 | $2078.03 | 17,907 |
| 2026-01-01 | Papamichael Michael A | Tax withholding | 131 | $2078.03 | 772 |
| 2026-01-01 | Hildreth Michaela | Tax withholding | 274 | $2078.03 | 2,491 |
| 2025-12-23 | Hildreth Michaela | Gift | 60 | $0.00 | 2,165 |
| 2025-12-19 | Rountree George Manning | Open-market sale | 5,000 | $2050.00 | 13,809 |
| 2025-12-19 | CAMPBELL REID TARLTON | Open-market sale | 5,000 | $0.00 | 10,440 |
| 2025-12-19 | CAMPBELL REID TARLTON | Open-market sale | 5,000 | $2050.00 | 10,440 |
| 2025-12-16 | Gelston Philip A | Open-market sale | 165 | $2048.51 | 1,568 |
| 2025-11-25 | CAMPBELL REID TARLTON | Gift | 50 | $0.00 | 15,440 |
| 2025-11-10 | Tanner David Allen | Gift | 4 | $0.00 | 2,104 |
| 2025-05-22 | CAMPBELL REID TARLTON | Grant / award | 150 | $0.00 | 15,490 |
| 2025-05-22 | Carlson Peter M | Grant / award | 150 | $0.00 | 717 |
| 2025-05-22 | CHOKSI MARY C | Grant / award | 150 | $0.00 | 1,858 |
| 2025-05-22 | Dillon Margaret | Grant / award | 150 | $0.00 | 945 |
| 2025-05-22 | Gelston Philip A | Grant / award | 150 | $0.00 | 1,733 |
| 2025-05-22 | Hicks Weston M | Grant / award | 210 | $0.00 | 2,746 |
Source: SEC EDGAR Form 4 filings. For informational purposes only — not investment advice.