Risk-of-ruin calculator

A 60% win-rate strategy can still bust before profit. This calculator gives the probability of ruin — busting the drawdown floor — under your stated win-rate, R:R, position size, and DD distance to ruin.

Risk of ruin

3.46%

Acceptable for a single attempt.

Edge per trade

16.67%

Normalised expectancy. Negative = strategy loses money on average.

Full-stop losses to ruin

10

How many consecutive max-risk losers wipe out the DD cushion.

How to use this calculator

  1. Enter win-rate. Percent of closed trades that finish in profit. Use the realised number, not your hopeful number.
  2. Enter reward:risk. Average reward divided by average risk. 1.5 means winning trades are 1.5× the size of losing trades on average.
  3. Enter risk-per-trade. Percent of equity at risk per trade (the stop-loss distance, expressed as % of balance).
  4. Enter ruin distance. Max drawdown you can sustain before the firm closes you out. For most firms: the overall DD percent.
  5. Read the ruin probability. Below 5% is solid; 5–15% is workable on a single attempt; above 25% — re-size or improve the strategy.

FAQ

Why is my ruin probability 100%?
Your expectancy per trade is zero or negative — winRate × R:R does not exceed (1 - winRate). The strategy loses money on average and ruin is mathematically certain over enough trades.
Why does the ruin number jump so much when I tweak risk-per-trade?
Ruin grows exponentially with risk-per-trade because more aggressive sizing means fewer losing trades push you to ruin. Halving the risk roughly squares the ruin probability.
Is this Kelly?
No — Kelly maximises long-run growth. This calculator measures the asymmetric "fail before profit" probability that matters when you face a hard drawdown floor.
Does this account for variable R:R?
No — it uses average R:R. Real strategies have variance; treat the output as an order-of-magnitude estimate, not a precise number.
What's the relationship between ruin probability and consecutive-loss probability?
Lossses to ruin = ruin distance ÷ risk per trade. A 10% DD with 1% risk needs 10 consecutive full-stop losses (or equivalent compound drawdown).

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