wtm-20260506

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions:

Securities registered pursuant to Section 12(b) of the Act:

Title of each class

Trading Symbol(s)

Name of each exchange on which registered

Common Shares, par value $1.00 per share

WTM

New York Stock Exchange

WTM.BH

Bermuda Stock Exchange

Indicate by check mark whether the registrant is an emerging growth company as defined in Rule 405 of the Securities Act of 1933(§230.405 of this chapter) or Rule 12b-2 of the Securities Exchange Act of 1934 (§240.12b-2 of this chapter). Emerging growth company ☐

If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act. o

On May 6, 2026, White Mountains Insurance Group, Ltd. issued a press release announcing its results for the three months ended March 31, 2026. The press release furnished herewith is attached as Exhibit 99.1 to this Form 8-K.

Certain information included in the press release constitutes non-GAAP financial measures (as defined in Regulation G of the Securities and Exchange Commission). Specifically, there are 10 non-GAAP financial measures: (i) Kudu’s EBITDA, (ii) Kudu’s adjusted EBITDA, (iii) Kudu’s annualized adjusted EBITDA, (iv) Kudu’s annualized revenue, (v) Kudu’s cash revenue yield, (vi) Distinguished’s ScaleCo net income (loss), (vii) Distinguished’s ScaleCo EBITDA, (viii) Distinguished’s ScaleCo adjusted EBITDA, (ix) total consolidated portfolio return excluding MediaAlpha and (x) total equity portfolio return excluding MediaAlpha. These non-GAAP financial measures have been reconciled from their most comparable GAAP financial measures.

Kudu’s EBITDA, adjusted EBITDA, annualized adjusted EBITDA, annualized revenue and cash revenue yield are non-GAAP financial measures. EBITDA is a non-GAAP financial measure that adds back interest expense on debt, income tax (expense) benefit, depreciation and amortization of other intangible assets to GAAP net income (loss). Adjusted EBITDA is a non-GAAP financial measure that excludes certain other items in GAAP net income (loss) in addition to those added back to calculate EBITDA. The items relate to (i) net realized and unrealized investment gains (losses) on Kudu’s revenue and earnings participation contracts, (ii) non-cash equity-based compensation expense and (iii) transaction expenses. A description of each item follows:

•Net realized and unrealized investment gains (losses) - Represents net unrealized investment gains and losses recorded on Kudu’s revenue and earnings participation contracts, which are recorded at fair value under GAAP, and realized investment gains and losses from participation contracts sold during the period.

•Transaction expenses - Represents costs directly related to Kudu’s mergers and acquisitions activity, such as external lawyer, banker, consulting and placement agent fees, which are not capitalized and are expensed under GAAP.

Annualized adjusted EBITDA is a non-GAAP financial measure that (i) annualizes partial year revenues related to Kudu’s revenue and earnings participation contracts acquired during the previous 12-month period and (ii) removes partial year revenues related to revenue and earnings participation contracts sold during the previous 12-month period. Annualized revenue is a non-GAAP financial measure that adds the adjustments for annualized adjusted EBITDA to GAAP net investment income. Cash revenue yield is a non-GAAP financial measure that is derived using annualized revenue as a percentage of total net capital drawn and invested. The most directly comparable GAAP financial measure is net investment income revenue yield, which is derived using GAAP net investment income as a percentage of total net capital drawn and invested.

White Mountains believes that these non-GAAP financial measures are useful to management and investors in evaluating Kudu’s performance. White Mountains also believes that annualized adjusted EBITDA is useful to management and investors in understanding the full earnings profile of Kudu’s business as of the end of any 12-month period. See page 14 of Exhibit 99.1 to this Form 8-K for the reconciliation of Kudu’s GAAP net income (loss) to EBITDA, adjusted EBITDA and annualized adjusted EBITDA, and the reconciliation of Kudu’s GAAP net investment income to annualized revenue.

Distinguished’s ScaleCo net income (loss), ScaleCo EBITDA and ScaleCo adjusted EBITDA are non-GAAP financial measures. ScaleCo net income (loss) is a non-GAAP financial measure that excludes the results of the GrowthCo vertical, which is consolidated under GAAP, from Distinguished’s consolidated GAAP net income (loss). ScaleCo EBITDA is a non-GAAP financial measure that adds back interest expense on debt, income tax (expense) benefit, depreciation and amortization of other intangible assets to ScaleCo net income (loss). ScaleCo adjusted EBITDA is a non-GAAP financial measure that excludes certain other items in GAAP net income (loss) in addition to those items added back to calculate ScaleCo EBITDA. The items relate to (i) non-cash equity-based compensation expense and (ii) restructuring expenses. A description of each item follows:

•Non-cash equity-based compensation expense - Represents non-cash expenses related to Distinguished’s management compensation that are settled with equity units in Distinguished.

White Mountains believes that these non-GAAP financial measures are useful to management and investors in evaluating Distinguished’s performance. White Mountains also believes that excluding the results of the GrowthCo vertical, which Distinguished views as an investment in start-up programs, is useful to understanding the performance of Distinguished’s established programs. See page 17 of Exhibit 99.1 to this Form 8-K for the reconciliation of Distinguished’s consolidated GAAP net income (loss) to ScaleCo net income (loss), ScaleCo EBITDA and ScaleCo adjusted EBITDA.

Total consolidated portfolio return excluding MediaAlpha and total equity portfolio return excluding MediaAlpha are non-GAAP financial measures that remove the net investment income and net realized and unrealized investment gains (losses) from White Mountains’s investment in MediaAlpha. White Mountains believes these measures to be useful to management and investors by showing the underlying performance of White Mountains’s investment portfolio and equity portfolio without regard to White Mountains’s investment in MediaAlpha. The following tables present reconciliations from GAAP to the reported percentages:


	Three Months Ended March 31,
	2026		2025
Total consolidated portfolio return	0.2	%	1.7	%
Remove MediaAlpha	0.8		0.6
Total consolidated portfolio return excluding MediaAlpha	1.0	%	2.3	%

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned thereunto duly authorized.


	Three Months Ended March 31, 2026
Total equity portfolio return		(0.3)	%
Remove MediaAlpha		1.9
Total equity portfolio return excluding MediaAlpha		1.6	%


Bermuda (State or other jurisdiction of incorporation or organization)			1-8993 (Commission file number)			94-2708455 (I.R.S. Employer Identification No.)