Risk of Ruin Calculator: Protect Your Trading Capital
Know your odds of survival before you scale exposure. This guide explains how to calculate risk of ruin, interpret the results, and build guardrails that keep your probability of blowing up near zero.
What Is Risk of Ruin?
Risk of ruin measures the probability that continued losses will push your account below a critical capital threshold. It combines your historical win rate, average reward-to-risk ratio, and risk per trade to estimate how many consecutive losses you can survive. Professional traders aim for ruin probabilities below 0.5%, ensuring they can weather bad streaks without catastrophic damage.
Key Inputs You Need
Gather accurate data before trusting any calculation.
Win Rate (W%)
Percentage of trades that end positive. Derive from at least 50-100 recorded trades.
Reward to Risk (RR)
Average profit size relative to average loss. 2:1 means average wins are twice as large as losses.
Risk per Trade (R%)
Capital at risk for each trade. Keep this between 0.5%-1.5% to keep ruin probabilities low.
Capital Buffer
Percentage drawdown at which you stop trading to preserve capital and edge.
DIY Risk of Ruin Formula Walkthrough
• Convert win rate (W) and loss rate (L = 1 - W) into decimal format.
• Calculate edge per trade: Edge = W × RR − L.
• Determine risk unit (R) as decimal (e.g., 1% = 0.01).
• Approximate risk of ruin using the Kelly-based formula: Ruin ≈ ((L / W) ^ capital buffer in R units).
• Cross-check using a Monte Carlo simulator or spreadsheet to account for variance.
For more precision, run 10,000 Monte Carlo simulations using your trade metrics. Compare simulated drawdowns with your risk appetite to validate position sizing.
Scenario Analysis
Conservative Trader
Win Rate 48%, RR 2.2, Risk per Trade 0.75%
Risk of ruin < 0.1% with 20R buffer. Suitable for steady compounding.
Aggressive Trader
Win Rate 42%, RR 1.5, Risk per Trade 2%
Risk of ruin climbs to 18% without a hard stop. Reduce risk per trade or improve RR.
Scalper Under Pressure
Win Rate 58%, RR 1.2, Risk per Trade 1.5%
Despite higher win rate, low RR elevates ruin probability to 9%. Consider scaling out winners.
Implementation Blueprint
• Build a spreadsheet or use risk management software to run monthly updates.
• Align your risk per trade with target ruin probability. Most full-time traders target ≤0.5%.
• Set trigger levels for reducing size or pausing trading once ruin probability exceeds your threshold.
• Communicate risk metrics to accountability partners or trading journal for transparency.
Capital Protection Checklist
• Set max daily loss equal to 3x risk per trade to cap streak damage.
• Reduce position size by 50% after three consecutive losses.
• Pause live trading if drawdown exceeds 8% and run diagnostic review.
• Maintain diversified playbook to avoid correlated strategy failure.
• Recalculate risk of ruin quarterly as your metrics evolve.
Common Mistakes to Avoid
- Overestimating win rate by counting demo or cherry-picked results.
- Ignoring correlation between strategies and assuming independence.
- Running high risk per trade because a strategy “feels” reliable.
- Failing to account for slippage and execution costs in RR calculations.
- Skipping periodic recalculation as market conditions change.
Key Takeaways
• Even good strategies can fail without proper position sizing.
• Keep risk per trade low enough that losing streaks are survivable.
• Update your ruin probabilities as performance metrics evolve.
• Combine quantitative analysis with hard behavioral guardrails.
Continue Learning
Money Management Rules
Build a ruleset that keeps your equity curve stable.
Drawdown Management
Plan recovery protocols before you hit critical capital thresholds.