Risk of Ruin Calculator: What Every Trader Should Know

What is Risk of Ruin?

Risk of ruin is the probability that a trader will lose enough capital to stop trading, calculated from win rate, position size, and risk-reward ratio. It is not about a single bad trade — it describes the statistical likelihood that a series of losses, even within a profitable strategy, will drain an account below a usable threshold. According to research on retail trading outcomes (ESMA, 2018), between 74% and 89% of retail CFD accounts lose money, suggesting that ruin probability is widely underestimated.

Most traders focus on win rate and ignore ruin probability entirely. This is a mistake.

The Formula

The classic risk of ruin formula for a fixed-fraction strategy is:

R = ((1 - Edge) / (1 + Edge))^Units

Where Edge = (Win% × Avg Win) - (Loss% × Avg Loss), and Units = Account / Risk Per Trade. As Dr. Ralph Vince demonstrated in *Portfolio Management Formulas* (Wiley, 1990), "the risk of ruin is not a function of the edge alone — it is a function of the edge relative to the bet size."

But this assumes independent, identically distributed trades. Real markets are messier.

Why Monte Carlo Matters

Monte Carlo simulation is a computational method that runs thousands of randomized trade sequences to show the full distribution of outcomes, not a single number. Unlike static formulas, Monte Carlo accounts for path dependency — the order in which wins and losses occur. A study by Krokhmal, Palmquist & Uryasev (University of Florida, 2002) found that path-dependent risk measures like Conditional Value at Risk (CVaR) capture tail risk that static formulas miss entirely.

With simulation-based analysis, you can observe:

• The probability of hitting a 50% drawdown
• The probability of total ruin
• The range of outcomes across pessimistic (P5), median (P50), and optimistic (P95) scenarios

These formulas describe the structure of risk, but their real impact depends on how strategies behave across repeated scenarios.

Approaches to Lowering Ruin Probability

1. Reduce risk per trade. Moving from 5% to 2% risk per trade can reduce ruin probability by 60–80%, depending on strategy parameters.

2. Improve your risk-reward ratio. A 1:2 risk-reward with 40% win rate may be survivable. A 1:1 with the same win rate is far more fragile.

3. Know your drawdown tolerance. If a 30% drawdown makes you change strategies, your real ruin threshold is 30%, not 100%.

Try It Yourself

Use the Risk of Ruin Calculator to explore your probability of ruin based on your trading stats. Or download RangeSight for full Monte Carlo analysis with real ticker data.

Conceptually this provides a framework. In practice, outcomes vary across simulations. Testing multiple scenarios reveals how consistent a strategy actually is.