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

SecurityWTM / White Mountains Insurance Group, Ltd.
InstitutionAdvisor Group Holdings, Inc.
Latest Disclosed Ownership650 shares
Latest Disclosed Value $ 1,428,008
Advisor Group Holdings, Inc. reports 58.54% increase in ownership of WTM / White Mountains Insurance Group, Ltd.

On May 15, 2026 - Advisor Group Holdings, Inc. filed a 13F-HR form disclosing ownership of 650 shares of White Mountains Insurance Group, Ltd. (US:WTM) valued at $1,428,024 USD as of March 31, 2026. The entity filed a previous 13F-HR on February 17, 2026 disclosing 410 shares of White Mountains Insurance Group, Ltd.. This represents a change in shares of 58.54% during the quarter. The current value of the position is $1,342,341 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 650 240 58.54 1,428 67.61 0.0012
2026-02-17 2025-12-31 13F WHITE MTNS INS GROUP COM G9618E107 410 -3 -0.73 852 16.71 0.0012
2025-11-14 2025-09-30 13F WHITE MTNS INS GROUP COM G9618E107 413 23 5.90 731 4.29 0.0010
2025-09-04 2025-06-30 13F/A-1 HITE MTNS INS GROUP COM G9618E107 390 19 5.12 701 -1.96 0.0012
2025-08-13 2025-06-30 13F HITE MTNS INS GROUP COM G9618E107 382 11 741 0.0009
2025-05-12 2025-03-31 13F WHITE MTNS INS GROUP COM G9618E107 371 -155 -29.47 714 -30.21 0.0016
2025-06-06 2024-12-31 13F/A-1 WHITE MTNS INS GROUP COM G9618E107 526 140 36.27 1,023 56.42 0.0023
2025-02-07 2024-12-31 13F WHITE MTNS INS GROUP COM G9618E107 380 -6 685 0.0017
2024-11-13 2024-09-30 13F WHITE MTNS INS GROUP COM G9618E107 386 -208 -35.02 655 -39.39 0.0015
2024-08-13 2024-06-30 13F WHITE MTNS INS GROUP COM G9618E107 594 231 63.64 1,080 65.75 0.0026
2024-05-10 2024-03-31 13F WHITE MTNS INS GROUP COM G9618E107 363 -729 -66.76 651 -60.38 0.0015
2024-02-12 2023-12-31 13F WHITE MTNS INS GROUP COM G9618E107 1,092 -366 -25.10 1,644 -24.63 0.0029
2023-11-13 2023-09-30 13F WHITE MTNS INS GROUP COM G9618E107 1,458 388 36.26 2,181 46.51 0.0032
2023-08-21 2023-06-30 13F/A-1 WHITE MTNS INS GROUP COM G9618E107 1,070 -31 -2.82 1,489 -1.85 0.0027
2023-08-10 2023-06-30 13F WHITE MTNS INS GROUP COM G9618E107 3,846 2,745 1,486 0.0004
2023-05-12 2023-03-31 13F WHITE MTNS INS GROUP COM G9618E107 1,101 20 1.85 1,517 -0.79 0.0029
2023-02-10 2022-12-31 13F WHITE MTNS INS GROUP COM G9618E107 1,081 -22 -1.99 1,529 6.33 0.0031
2022-11-14 2022-09-30 13F WHITE MTNS INS GROUP COM G9618E107 1,103 45 4.25 1,437 8.95 0.0033
2022-08-10 2022-06-30 13F WHITE MTNS INS GROUP COM G9618E107 1,058 -958 -47.52 1,319 -77.44 0.0029
2022-05-04 2022-03-31 13F WHITE MTNS INS GROUP COM G9618E107 2,016 -5 -0.25 5,847 185.64 0.0113
2022-02-03 2021-12-31 13F WHITE MTNS INS GROUP COM G9618E107 2,021 354 21.24 2,047 14.81 0.0039
2021-11-05 2021-09-30 13F WHITE MTNS INS GROUP COM G9618E107 1,667 -374 -18.32 1,783 -23.97 0.0037
2021-08-02 2021-06-30 13F WHITE MTNS INS GROUP COM G9618E107 2,041 114 5.92 2,345 9.12 0.0051
2021-05-13 2021-03-31 13F WHITE MTNS INS GROUP COM G9618E107 1,927 42 2.23 2,149 13.94 0.0052
2021-02-10 2020-12-31 13F WHITE MTNS INS GROUP COM G9618E107 1,885 41 2.22 1,886 30.61 0.0050
2020-11-12 2020-09-30 13F WHITE MTNS INS GROUP COM G9618E107 1,844 996 117.45 1,444 92.02 0.0043
2020-08-14 2020-06-30 13F WHITE MTNS INS GROUP COM G9618E107 848 -52 -5.78 752 -8.29 0.0025
2020-05-18 2020-03-31 13F WHITE MTNS INS GROUP COM G9618E107 900 900 820 0.0034
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.