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White Mountains Insurance Group stock timeline
A year of the price with every insider trade, planned sale, earnings report and material 8-K marked
252 sessions+18.4% to $2,241.12
White Mountains Insurance Group (WTM) stock rose 18% over the last 252 sessions, to $2,241.12. On the way it reported 0 quarters, its insiders filed 2 open-market trades, and the company filed 4 material 8-Ks. Each is marked on the price and listed with what the stock did next.
Each mark, and what followed
| Date | Kind | What | Next session | 5 sessions | 21 sessions |
|---|---|---|---|---|---|
| Aug 27, 2026 | 8-K | Directors and officers: departures, appointments, pay | −0.2% (−0.9% vs SPY) | −1.3% (−1.2% vs SPY) | −5.0% (−5.9% vs SPY) |
| May 21, 2026 | 8-K | Directors and officers: departures, appointments, pay | +0.4% (0.0% vs SPY) | −3.5% (−5.4% vs SPY) | −5.6% (−4.6% vs SPY) |
| May 15, 2026 | 8-K | Material definitive agreement | +1.1% (+2.3% vs SPY) | +1.2% (+2.0% vs SPY) | −4.0% (−4.9% vs SPY) |
| Dec 19, 2025 | Insider sale | Rountree George Manning sold $10.2M | +0.1% (−0.8% vs SPY) | +1.1% (−1.2% vs SPY) | +1.6% (0.0% vs SPY) |
| Dec 16, 2025 | Insider sale | Gelston Philip A sold $338K | −1.1% (−0.8% vs SPY) | +0.7% (−0.2% vs SPY) | −0.3% (−2.3% vs SPY) |
| Dec 8, 2025 | 8-K | Completed acquisition or disposition | −1.1% (−0.8% vs SPY) | +1.0% (+1.5% vs SPY) | +1.2% (+0.4% vs SPY) |
Insiders’ record here
In the year on the chart, White Mountains Insurance Group's insiders reported 0 open-market buys ($0) and 2 sales ($10.6M). Of the 2 old enough to score, 0 were followed by the stock doing what the trade implied over the next 63 sessions (beating SPY after a buy, lagging it after a sale); the median excess return after a buy was — and after a sale +12.3%.
Across the whole universe (19,782 scored trades), insider buys beat the market 46% of the time and sales were followed by a lagging stock 61% of the time; buys of $1M or more 39%. Every pattern →
What this kind of 8-K usually did
| Item | 8-Ks | Next session, median | Up next session | 21 sessions, median | Typical size |
|---|---|---|---|---|---|
| 2.01 Completed acquisition or disposition | 2,671 | +0.1% | 52% | +1.2% | ±1.6% |
| 1.01 Material definitive agreement | 23,525 | 0.0% | 51% | +1.0% | ±1.4% |
| 2.03 New debt or off-balance-sheet obligation | 13,268 | 0.0% | 50% | +1.2% | ±1.3% |
| 5.02 Directors and officers: departures, appointments, pay | 39,174 | −0.1% | 48% | +0.7% | ±1.4% |
Across every company in the move-odds universe, measured from the close before the filing. Every 8-K item ranked →
White Mountains Insurance Group: every quarter → Live insider trades →
Prices are daily closes; filings and trades are as filed with the SEC (Form 4 within two business days of the trade, 8-K within four of the event). Moves after a mark are the stock's close-to-close change and the same for SPY; they describe the record, not what the next one will do. Not investment advice.