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AI brief of an SEC Form 8-K · WHITE MOUNTAINS INSURANCE GROUP LTD (WTM)

White Mountains posts $39 million Q3 loss as book value per share falls 1%

Negative Impact 3 of 5 earnings Written later

White Mountains Insurance Group reported a net loss attributable to common shareholders of $39 million for the third quarter of 2026, compared with income of $114 million a year earlier, and book value per share fell 1% to $2,243 as of September 30, 2026. Unrealized investment losses, including a $54 million mark-to-market loss on its MediaAlpha stake after a 24% share price decline, drove the result, which matters to shareholders because the book value per share is the company's main measure of value.

Key points

  • Third-quarter 2026 net income (loss) attributable to common shareholders was $(39) million, versus $114 million in Q3 2025; first nine months were $133 million, versus $271 million.
  • Third-quarter total revenues were $641 million, down from $864 million in Q3 2025.
  • Book value per share was $2,243 at September 30, 2026, down 1% for the quarter and up 3% for the first nine months, including dividends.
  • On November 4, 2026, the company agreed to sell 5.5 million MediaAlpha shares at $13.90 per share, leaving it with 12.4 million shares.

The filing

CompanyWHITE MOUNTAINS INSURANCE GROUP LTD (WTM)
Form8-K, current report
Filed with the SECNov 5, 2026, 8:13 AM ET
Accession number0001628280-26-070627

Items reported: 2.02 Results of Operations

Read the filing on SEC.gov ↗

Written by AI on Nov 9, 2026, 8:51 AM ET, from this filing only. Written later: this filing was briefed after the fact, when past filings were added to the site, so the brief may be read with hindsight; the filing itself is the record of what was known on November 05, 2026.

Briefs are written by AI from the filing text and can contain mistakes — open the filing before acting on anything. Impact (1-5) and tone are the AI's reading of the filing for shareholders, not a price forecast. Not investment advice.