Win rate is the stat traders brag about; risk of ruin is the stat that decides whether the account still exists in six months. It is the probability that a strategy, with its exact win rate and reward-to-risk, hits your account’s ruin threshold before it profits.
The formula
Edge per unit risked = (win rate × reward-to-risk) − loss rate. Risk of ruin ≈ ((1 − edge) ÷ (1 + edge))N, where N is how many of your risk units the drawdown limit absorbs. Example: 45% win rate at 2:1 gives edge 0.35. On an account whose 10% limit survives ten 1% losses: 0.6510 ≈ 1.3% risk of ruin. Same strategy at 2% risk: cushion of 5 losses, 0.655 ≈ 11.6%. Same trading, ten times the death probability. Compute yours with the risk of ruin calculator.
Why cushion beats win rate
Traders chase win rate because losses feel like failure. The math disagrees about what to fix first: going from 45% to 55% win rate at 2:1 cuts risk of ruin by roughly half; halving your risk size cuts it by a power. Cushion is the variable you control today, at zero cost to your strategy.
Streaks are normal
A 45% win-rate strategy produces losing streaks of 8-10 trades several times per thousand trades, regularly enough to meet in a normal year. If your cushion is five losses, you are not unlucky when it happens, you were structurally doomed. This is the real reason evaluation passers trade 0.25-0.5% risk: they are buying enough streak insurance for the expected trade count to actually finish the target.
The honest conclusion
No positive-expectancy strategy is “safe” at too large a size, and no negative-expectancy strategy is saved by small size. Risk of ruin is where position sizing (see the position sizing guide), drawdown rules (see the drawdown guide) and your payout plan all meet. It is the number to check before the first trade of any funded cycle.
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Educational content only, not financial advice. See our disclaimer.