White Mountains Insurance Group, Ltd.
US ˙ NYSE ˙ BMG9618E1075

SecurityWTM / White Mountains Insurance Group, Ltd.
InstitutionCerity Partners LLC
Latest Disclosed Ownership1,867 shares
Latest Disclosed Value $ 4,101,724
Cerity Partners LLC reports 47.30% decrease in ownership of WTM / White Mountains Insurance Group, Ltd.

On May 15, 2026 - Cerity Partners LLC filed a 13F-HR form disclosing ownership of 1,867 shares of White Mountains Insurance Group, Ltd. (US:WTM) valued at $4,101,724 USD as of March 31, 2026. The entity filed a previous 13F-HR on February 11, 2026 disclosing 3,543 shares of White Mountains Insurance Group, Ltd.. This represents a change in shares of -47.30% during the quarter. The current value of the position is $3,797,515 USD.

Institutional Ownership: 13F and NPORT Filings

The Security and Class in the table below are shown exactly as filed by the investor. We do our best to track continuity of investments through acquisitions, and this will be reflected in the table as changes in names. In addition to descriptive data, performance of the investment is shown over time. To calculate quarterly performance, we first calculate cost basis of the shares purchased during the quarter, then use that to calculate gross profit. Quarterly return is Gross Profit / Starting Portfolio value.

Note that cost basis is calculated and stored in thousands, so small quarterly changes in shares frequently result in a cost basis of zero.

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Disclosed Equity Positions (from 13F/NPORT Filings)
File
Date		 Effective
Date		Form Security Class ID Avg Price
Paid (Est)		 Reported
Shares		 ΔShares ΔShares
(%)		 Reported
Value
(x1000)		 ΔValue
(%)		 Alloc
(%)		 ΔAlloc ΔAlloc (%) Cost Basis
(x1000)		 Unrealized
Gain/Loss
(x1000)
2026-05-15 2026-03-31 13F WHITE MTNS INS GROUP COM G9618E107 1,867 -1,676 -47.30 4,102 -44.30 0.0058
2026-02-11 2025-12-31 13F WHITE MTNS INS GROUP COM G9618E107 3,543 1,603 82.63 7,362 127.08 0.0107
2025-10-22 2025-09-30 13F WHITE MTNS INS GROUP COM G9618E107 1,940 40 2.11 3,243 -4.95 0.0053
2025-08-13 2025-06-30 13F WHITE MTNS INS GROUP Stock G9618E107 1,900 4 0.21 3,412 -6.57 0.0061
2025-04-30 2025-03-31 13F WHITE MTNS INS GROUP Stock G9618E107 1,896 48 2.60 3,651 1.84 0.0074
2025-02-13 2024-12-31 13F WHITE MTNS INS GROUP Stock G9618E107 1,848 133 7.76 3,586 23.28 0.0078
2024-11-12 2024-09-30 13F WHITE MTNS INS GROUP Stock G9618E107 1,715 -14 -0.81 2,909 -7.45 0.0064
2024-08-13 2024-06-30 13F WHITE MTNS INS GROUP COM G9618E107 1,729 124 7.73 3,142 9.14 0.0083
2024-05-14 2024-03-31 13F WHITE MTNS INS GROUP Stock G9618E107 1,605 79 5.18 2,880 25.34 0.0076
2024-01-26 2023-12-31 13F WHITE MTNS INS GROUP Stock G9618E107 1,526 42 2.83 2,297 3.52 0.0075
2023-11-14 2023-09-30 13F WHITE MTNS INS GROUP COM G9618E107 1,484 -244 -14.12 2,220 -7.50 0.0108
2023-08-14 2023-06-30 13F WHITE MTNS INS GROUP Stock G9618E107 1,728 147 9.30 2,400 10.20 0.0093
2023-05-11 2023-03-31 13F WHITE MTNS INS GROUP Stock G9618E107 1,581 1,284 432.32 2,178 418.33 0.0051
2023-02-15 2022-12-31 13F WHITE MTNS INS GROUP COM G9618E107 297 20 7.22 420 16.34 0.0027
2022-11-14 2022-09-30 13F WHITE MTNS INS GROUP Stock G9618E107 277 0 0.00 361 4.64 0.0043
2022-08-10 2022-06-30 13F WHITE MTNS INS GROUP STOCK G9618E107 277 77 38.50 345 51.98 0.0038
2022-04-25 2022-03-31 13F WHITE MTNS INS GROUP Stock G9618E107 200 -58 -22.48 227 -13.03 0.0035
2022-02-14 2021-12-31 13F WHITE MTNS INS GROUP Stock G9618E107 258 43 20.00 261 13.48 0.0040
2021-10-25 2021-09-30 13F White Mountains Insurance Group Stock G9618E107 215 0 0.00 230 -6.88 0.0051
2021-08-11 2021-06-30 13F WHITE MTNS INS GROUP Stock G9618E107 215 0 0.00 247 2.92 0.0054
2021-08-11 2021-03-31 13F/A-1 WHITE MTNS INS GROUP Stock G9618E107 215 0 0.00 240 11.63 0.0057
2021-05-12 2021-03-31 13F WHITE MTNS INS GROUP Stock G9618E107 215 0 240 0.0071
2021-02-11 2020-12-31 13F WHITE MTNS INS GROUP Stock G9618E107 215 215 215 0.0069
2020-05-14 2020-03-31 13F WHITE MTNS INS GROUP COM G9618E107 0 -200 -100.00 0 -100.00
2020-02-14 2019-12-31 13F WHITE MTNS INS GROUP COM G9618E107 200 -1 -0.50 223 2.76 0.0114
2019-10-30 2019-09-30 13F WHITE MTNS INS GROUP COM G9618E107 201 1 0.50 217 6.37 0.0127
2019-08-14 2019-06-30 13F WHITE MTNS INS GROUP COM G9618E107 200 -21 -9.50 204 -0.49 0.0129
2019-05-14 2019-03-31 13F WHITE MTNS INS GROUP COM G9618E107 221 221 205 0.0138
2019-02-06 2018-12-31 13F WHITE MTNS INS GROUP COM G9618E107 0 -218 -100.00 0 -100.00
2018-11-15 2018-09-30 13F WHITE MTNS INS GROUP COM G9618E107 218 218 204 0.0141
Legend
Shares
The total number of shares held by the institution at the end of the reporting period (the effective date). This is provided in the filing.
Value
The total value of the shares as of the effective date. This is provided in the filing.
Avg. Share Price
The weighted average share price of the shares held by the institution. We use FIFO accounting to determine this price
Class
This is the security class as indicated by the filer. There are a variety of values for this field. Common values include "EC" = equity common, "EP" - equity preferred
Allocation (%)
The percent of the institution's portfolio that this position represents. This is provided in NPORT filings. For 13F filings, we calculate it.
Change in Allocation
The change in allocation from the prior reporting period. This is calculated as current allocation - prior allocation.
Change in Allocation (%)
The percent change in allocation from the prior reporting period. This is calculated as (current allocation - prior allocation) / prior allocation.
Cost Basis
The total cost of the shares held. This is calculated as reported shares * avg. share price
Unrealized Gain/Loss
This is the market value of the position as of the effective date minus the cost basis.