Risk of ruin calculates the probability that a trader will lose a specified portion of their capital, even with a profitable strategy, based on their win rate, payoff ratio, and risk per trade — making it the definitive test of whether your position sizing will keep you alive.
What Is Risk of Ruin?
Risk of ruin answers the most fundamental question in trading: will I survive?
Having a profitable strategy is necessary but not sufficient. If your position sizing is too aggressive, a normal losing streak — one that is statistically inevitable over hundreds of trades — can destroy your account before your edge has time to produce results.
Risk of ruin quantifies this probability. It tells you the likelihood that your trading account hits a catastrophic drawdown threshold given your specific combination of win rate, reward-to-risk ratio, and position size.
The Risk of Ruin Formula
The classic formula adapted for trading:
RoR = ((1 - Edge) / (1 + Edge)) ^ Capital Units
Where:
- Edge = (Win Rate x Payoff Ratio) - Loss Rate
- Capital Units = 1 / Risk Per Trade (as decimal)
Step-by-Step Calculation
For a trader with 52% win rate, 1.5:1 payoff ratio, risking 2% per trade:
- Edge = (0.52 x 1.5) - 0.48 = 0.78 - 0.48 = 0.30
- Capital Units = 1 / 0.02 = 50
- RoR = ((1 - 0.30) / (1 + 0.30))^50 = (0.70 / 1.30)^50 = (0.5385)^50
This yields a risk of ruin of approximately 0.000000001% — essentially zero. The combination of positive edge and conservative sizing makes survival virtually certain.
Now the same edge at 5% risk per trade:
- Capital Units = 1 / 0.05 = 20
- RoR = (0.5385)^20 = approximately 0.0001% — still very low, but orders of magnitude higher
And at 10% risk per trade:
- Capital Units = 1 / 0.10 = 10
- RoR = (0.5385)^10 = approximately 0.21%
The same strategy goes from near-zero ruin risk to a meaningful one simply by changing position size.
Why Risk of Ruin Matters
Positive Expectancy Does Not Guarantee Survival
This is the most counterintuitive fact in trading mathematics. Consider a strategy with a slight edge — 51% win rate, 1:1 payoff ratio. The expectancy is positive:
(0.51 x $100) - (0.49 x $100) = $2 per trade
But at 10% risk per trade, the risk of ruin is above 40%. Nearly half the time, the account hits zero before the edge plays out.
The edge is real but fragile. Position sizing is the armor that protects it.
Losing Streaks Are Inevitable
With a 55% win rate, the probability of 10 consecutive losses is 0.45^10 = 0.034% per specific sequence. That sounds rare. But over 1,000 trades, you will encounter multiple losing streaks of 7-8 trades, and a streak of 10+ becomes likely. At 3% risk per trade, 10 consecutive losses creates a 26% drawdown — requiring 35% gains to recover.
Risk of Ruin and Prop Firm Trading
Prop firm traders face a stricter version of this problem. Instead of total account loss, “ruin” is hitting the firm’s maximum drawdown limit (typically 5-12%).
This changes the calculation dramatically. A strategy with 0.001% risk of total account ruin might have a 15-25% risk of hitting a 10% drawdown threshold. Every prop firm trader should run this calculation with their firm’s specific limits.
Example: FTMO Challenge
- Win rate: 50%
- Payoff ratio: 2:1
- Risk per trade: 1%
- Ruin threshold: 10% drawdown (FTMO’s maximum)
The risk of hitting the 10% drawdown limit is significantly higher than the risk of total account loss. Understanding this probability helps you choose the right risk per trade for challenge-specific constraints.
How Risk Per Trade Changes Everything
The table below shows risk of ruin for a strategy with 55% win rate and 1.5:1 payoff ratio at different position sizes:
| Risk Per Trade | Risk of Ruin (100%) | Risk of 25% Drawdown | Risk of 10% Drawdown |
|---|---|---|---|
| 0.5% | ~0% | ~0% | ~2% |
| 1% | ~0% | ~0.1% | ~8% |
| 2% | ~0% | ~3% | ~22% |
| 3% | ~0.001% | ~12% | ~38% |
| 5% | ~0.1% | ~31% | ~56% |
| 10% | ~5% | ~58% | ~78% |
The same profitable strategy ranges from near-invincible to almost certainly doomed depending solely on position sizing.
When to Use This Calculator
- Before live trading — verify your position sizing gives you a reasonable survival probability
- When choosing risk per trade — find the maximum risk that keeps ruin probability below your tolerance (typically below 1%)
- Prop firm preparation — model the probability of hitting drawdown limits before starting a challenge
- After strategy changes — recalculate with new win rate and payoff ratio parameters
- During drawdowns — reassess whether your current positioning is sustainable
Common Mistakes
Using Theoretical Instead of Actual Statistics
Your risk of ruin calculation is only as accurate as the inputs. Using a hypothetical 60% win rate when your journal shows 51% produces dangerously optimistic results. Always use real data from 100+ trades.
Ignoring Correlation
The formula assumes each trade is independent. In reality, forex trades can be correlated — if you take three long EUR/USD positions simultaneously and the dollar strengthens, all three lose. Correlated losses create effective position sizes much larger than your per-trade risk suggests.
Not Accounting for Psychological Ruin
Mathematical ruin is reaching zero. Psychological ruin is reaching a drawdown where you abandon your strategy, start revenge trading, or quit. For most traders, the psychological ruin point is 25-40% drawdown — long before mathematical ruin. Set your ruin threshold accordingly.
Forgetting That Edge Degrades
Market conditions change. A strategy that showed 55% win rate over the last 200 trades may degrade to 48% as volatility shifts. Build a safety margin into your risk of ruin calculations by using slightly worse statistics than your historical data suggests.
Risk of Ruin and Your Trading Journal
Risk of ruin is not a calculation you do once. It is a living metric that your trading journal should track continuously.
PipJournal monitors the inputs to risk of ruin in real time:
- Rolling win rate — how your win rate trends over recent trades
- Payoff ratio shifts — whether your average win and loss sizes are changing
- Risk consistency — whether you are actually risking what you think you are risking
- Drawdown proximity — how close you are to your personal or prop firm ruin threshold
- Correlation alerts — when multiple open positions create concentrated exposure
The co-pilot can flag when your current statistics produce a risk of ruin above your acceptable threshold, giving you time to reduce position sizes before a drawdown becomes critical.
Use the drawdown calculator to understand recovery math, and the expectancy calculator to verify your edge is real before sizing your positions.
Let PipJournal calculate your live risk of ruin from actual trading data so you can size positions with confidence, not guesswork.
