Risk of Ruin Explained
Risk of ruin is the probability that a string of losses wipes out your account before your edge can play out. It is why position sizing, not prediction, keeps traders alive.
What is risk of ruin?
Even a profitable strategy loses many trades in a row eventually. Risk of ruin measures the chance that such a losing streak drains your capital below the point of recovery. It depends on three things: your win rate, your reward-to-risk, and — most powerfully — how much of the account you risk per trade.
The key insight is non-linear: doubling your per-trade risk more than doubles your risk of ruin. Risking 10% per trade can make ruin almost certain over time even with a genuine edge, while 1% risk makes it vanishingly small.
Controlling it
Fix risk as a small, constant percentage of equity per trade (commonly 0.5–2%), size the position from your stop distance rather than a fixed lot, and enforce a daily loss cap. This is exactly the discipline prop firms encode in their drawdown rules.
Pair small per-trade risk with a positive reward-to-risk ratio and a realistic win rate, and the probability of ruin drops toward zero — the account survives long enough for the edge to compound.
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Play Chart Bound free → Try today's Call the Candle →Frequently asked questions
What is a safe risk per trade?
Most risk frameworks use 0.5% to 2% of account equity per trade. Lower per-trade risk dramatically reduces the probability of a losing streak ending the account.
Can a winning strategy still go to ruin?
Yes. If per-trade risk is large enough, a normal losing streak can wipe the account before the positive expectancy compounds. Position sizing, not just win rate, determines survival.
How is risk of ruin related to prop firm drawdown rules?
Prop firm daily-loss and max-drawdown limits are effectively a hard risk-of-ruin cap imposed on you — they force the small, consistent sizing that keeps ruin probability low.