SCHEDULE VI - SUPPLEMENTAL INFORMATION CONCERNING PROPERTY AND CASUALTY INSURANCE OPERATIONS

12 Months Ended

Dec. 31, 2025

SEC Schedule, 12-18, Supplemental Information, Property-Casualty Insurance Underwriters [Abstract]

SCHEDULE VI - SUPPLEMENTAL INFORMATION CONCERNING PROPERTY AND CASUALTY INSURANCE OPERATIONS

WHITE MOUNTAINS INSURANCE GROUP, LTD.

SUPPLEMENTAL INFORMATION CONCERNING PROPERTY AND CASUALTY INSURANCE OPERATIONS

(Millions)

Column A	Column B		Column C		Column D		Column E		Column F		Column G		Column H				Column I		Column J		Column K
	Deferred acquisition costs		Reserves for Unpaid Claims and Claims Adjustment Expenses		Discount, if any, deducted in Column C		Unearned Premiums		Earned Premiums		Net investment income		Claims and Claims Adjustment Expenses Incurred Related to				Amortization of deferred policy acquisition costs		Paid Claims and Claims Adjustment Expenses		Net Premiums written
Affiliation  with registrant													Current Year		Prior Year
Ark/WM Outrigger
2025	$	211.1	$	2,481.0	$	—	$	1,026.1	$	1,697.4	$	106.5	$	956.9	$	(112.7)	$	374.4	$	585.7	$	1,811.6
2024	165.2		2,127.5		—		853.3		1,587.8		90.7		914.4		(58.6)		294.1		416.7		1,679.1
2023	145.3		1,605.1		—		743.6		1,409.7		61.4		706.9		19.9		273.1		407.9		1,520.9
Bamboo Captive (1)
2025	$	—	$	—	$	—	$	—	$	26.7	$	1.8	$	16.0	$	2.0	$	9.7	$	27.2	$	16.1
2024	10.2		17.8		—		31.5		39.4		1.4		17.3		3.3		14.1		12.0		50.0
2023	—		—		—		—		—		—		—		—		—		—		—
Bamboo CRVs
2025	$	2.5	$	13.6	$	—	$	9.6	$	22.2	$	1.5	$	16.2	$	3.8	$	8.3	$	16.4	$	1.4
2024	5.8		12.1		—		29.0		32.7		.4		12.1		—		12.1		—		61.7
2023	—		—		—		—		—		—		—		—		—		—		—

(1) The Bamboo Captive’s results are from January 1, 2025 through December 5, 2025, the date of sale.