Risk of Ruin Calculator
Free Risk ruin Calculator for risk management. Enter your numbers to see returns, costs, and optimized scenarios instantly.
Reviewed for accuracy by Daniel Agrici, Founder & Lead Developer
Risk of Ruin Calculator
Calculator
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Formula: RoR = ((1 - edge) / (1 + edge))^N where edge = WR x (1 + W/L ratio) - 1
Worked example — Risk of ruin: < 0.01%. Kelly fraction: 25%. Very safe position sizing at 1/25th Kelly.
Formula
RoR = ((1 - edge) / (1 + edge))^N where edge = WR x (1 + W/L ratio) - 1
Risk of ruin is calculated by raising the ratio (1-edge)/(1+edge) to the power of N, where N represents the number of risk units needed to reach the ruin threshold. The edge is determined by multiplying win rate by (1 + win/loss ratio) and subtracting 1. Kelly Criterion = WR - LR / (W/L ratio).
Worked Examples
Example 1: Conservative Day Trader
Problem:A day trader has 55% win rate, 1.5:1 reward-to-risk, risks 1% per trade on a $25,000 account. Ruin threshold is 30%.
Solution:Edge = 0.55 x (1 + 1.5) - 1 = 0.55 x 2.5 - 1 = 0.375 Kelly = 0.55 - 0.45/1.5 = 0.55 - 0.30 = 0.25 (25%) Using 1% risk = 1/25th of Kelly (very conservative) Consecutive losses to ruin: log(0.70)/log(0.99) = ~35 trades Risk of ruin at 1% risk is extremely low.
Result:Risk of ruin: < 0.01%. Kelly fraction: 25%. Very safe position sizing at 1/25th Kelly.
Example 2: Aggressive Swing Trader
Problem:A swing trader has 45% win rate, 2:1 reward-to-risk, risks 5% per trade on $10,000. Ruin threshold is 40%.
Solution:Edge = 0.45 x (1 + 2) - 1 = 0.45 x 3 - 1 = 0.35 Kelly = 0.45 - 0.55/2 = 0.45 - 0.275 = 0.175 (17.5%) Using 5% risk = ~28% of Kelly Consecutive losses to ruin: log(0.60)/log(0.95) = ~10 trades Higher risk due to aggressive sizing.
Result:Risk of ruin: ~3.5%. Kelly fraction: 17.5%. Moderate risk — consider reducing to 2-3% per trade.
Frequently Asked Questions
What is the risk of ruin in trading and why does it matter?
Risk of ruin is the probability that a trader will lose enough capital to reach a point where they can no longer trade effectively, typically defined as losing a specified percentage of their account balance. This concept is fundamental to trading survival because even profitable strategies can lead to account blowup if position sizing is too aggressive. A trader with a genuine 55 percent win rate and positive expected value can still face ruin if they risk too much per trade, as a string of losses can deplete the account before the statistical edge manifests. The mathematics of risk of ruin demonstrates that capital preservation is not merely conservative advice but a mathematical necessity. Professional traders and fund managers calculate their risk of ruin to determine the maximum acceptable position size that keeps the probability of catastrophic loss below an acceptable threshold, typically under 1 to 5 percent.
How does position sizing affect the probability of ruin?
Position sizing has an exponential impact on risk of ruin, making it arguably the most important variable in a trading system. Doubling the risk per trade does not merely double the risk of ruin — it can increase it by an order of magnitude or more. For example, a trader with a 55 percent win rate and 1.5 reward-to-risk ratio might have a 0.1 percent risk of ruin when risking 1 percent per trade, but that same trader risking 5 percent per trade could face a 20 percent or higher probability of ruin. This dramatic escalation occurs because larger position sizes require fewer consecutive losses to reach the ruin threshold, and the probability of experiencing a specific losing streak increases substantially over hundreds or thousands of trades. Professional risk managers typically recommend never risking more than 1 to 2 percent of account equity on any single trade to maintain an acceptably low risk of ruin over a trading career.
What is the Kelly Criterion and how does it relate to risk of ruin?
The Kelly Criterion is a mathematical formula that calculates the optimal fraction of capital to risk on each trade to maximize the long-term geometric growth rate of the portfolio. The formula is Kelly Fraction equals Win Rate minus (Loss Rate divided by Win-to-Loss Ratio). While the full Kelly percentage theoretically maximizes growth, it also produces significant drawdowns and a relatively high risk of ruin in practice. Most professional traders use fractional Kelly, typically one-quarter to one-half of the full Kelly amount, to dramatically reduce volatility and risk of ruin while sacrificing only modest long-term growth. For instance, if full Kelly suggests risking 8 percent per trade, using half-Kelly at 4 percent cuts the growth rate by only about 25 percent but reduces the risk of a 50 percent drawdown by more than 75 percent. This demonstrates the asymmetric benefit of conservative position sizing.
How do win rate and reward-to-risk ratio interact in risk calculations?
Win rate and reward-to-risk ratio are the two components that define a trading edge, and they interact multiplicatively to determine expected value and risk of ruin. A trader can be profitable with a low win rate if the reward-to-risk ratio compensates sufficiently. For example, a trend-following system with only 35 percent win rate but a 3:1 average winner-to-loser ratio has a positive expected value of 0.35 times 3 minus 0.65 equals 0.40 per unit risked. Conversely, a scalping system with 70 percent win rate but only 0.8:1 reward ratio has an edge of 0.70 times 0.8 minus 0.30 equals 0.26 per unit risked. The first system has a higher mathematical edge despite winning far less frequently. When calculating risk of ruin, both variables feed into the edge calculation, and even small changes in either can dramatically alter the ruin probability, especially at higher risk-per-trade levels.
What is a safe risk of ruin percentage for different types of traders?
Acceptable risk of ruin thresholds vary by trader type, capital base, and ability to replenish funds. Professional fund managers and institutional traders typically target a risk of ruin below 0.1 percent, meaning there is less than a 1-in-1000 chance of reaching their maximum drawdown threshold. Full-time independent traders who depend on trading income generally aim for under 1 percent risk of ruin, providing strong statistical confidence in long-term survival. Part-time traders with separate income sources may accept 2 to 5 percent risk of ruin since they can potentially replenish trading capital from other earnings. Beginners and traders still developing their edge should be the most conservative, targeting well under 1 percent, because their actual win rate and reward statistics often deteriorate under live market conditions compared to backtesting results. A common mistake is estimating risk of ruin using optimistic performance parameters rather than worst-case realistic figures.
What are the different lot sizes in forex and how do they affect risk?
A standard lot is 100,000 units, a mini lot is 10,000, a micro lot is 1,000, and a nano lot is 100 units of the base currency. Smaller lots reduce your dollar-per-pip exposure, making them suitable for beginners or smaller accounts.
How do I calculate position size for proper risk management?
Determine your risk per trade (typically 1-2% of account balance), set your stop-loss distance in pips, then divide the dollar risk by the pip value to get the correct number of lots. This ensures consistent risk regardless of the pair or stop-loss width.
References
Reviewed for accuracy by Daniel Agrici, Founder & Lead Developer · Editorial policy
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