Kelly Criterion Calculator
Find the theoretically optimal risk per trade from your win rate and reward-to-risk, and see safer fractional Kelly sizes.
What is the Kelly criterion?
The Kelly criterion is a formula for the bet size that maximizes long-run growth, given your probability of winning and your payoff. For trading it becomes:
Kelly % = Win rate − (Loss rate ÷ Reward-to-risk)
With a 45% win rate and 2R average winners, Kelly = 0.45 − (0.55 ÷ 2) = 0.175, or 17.5% of the account per trade. That is far more than almost any professional trader risks.
Why traders use fractional Kelly
Full Kelly assumes your win rate and reward-to-risk are known exactly. In reality they are estimates, and full Kelly produces very deep drawdowns. Many traders use a quarter of Kelly or less, or simply cap risk at 0.5% to 2%, especially under prop firm drawdown limits.
A negative Kelly means no edge
If the formula gives zero or a negative number, your numbers show no positive expectancy and the optimal bet is nothing. Fix the strategy before sizing up.
Use real numbers
Kelly is only as good as its inputs. Clarity Tracking calculates your real win rate and average win and loss from synced trades, so you can size from data rather than guesses.
