Measure your edge / Free calculator
Kelly Criterion Calculator
The Kelly criterion calculates the bankroll fraction that maximizes expected logarithmic growth under an assumed probability model. Fractional Kelly scales that theoretical allocation down.
Your inputs
Instant calculationChanging formats resets odds to even money.
Your results
Based on your inputs. Before fees, rounding, and venue-specific settlement rules.
How to use the kelly criterion calculator
Enter the price, estimated chance of winning, bankroll, and a Kelly fraction. Full Kelly uses the entire calculated allocation; half or quarter Kelly scales it by 0.50 or 0.25. Negative-edge inputs return a zero stake.
Full Kelly = max(0, (p × decimal odds − 1) / (decimal odds − 1)); stake = bankroll × full Kelly × chosen fractionA worked example
With +100 odds and a 55% estimated chance of winning, full Kelly is 10% of bankroll. On a $1,000 bankroll that is $100. Half Kelly is $50 and quarter Kelly is $25.
What the numbers can tell you
Kelly is sensitive to probability error and assumes a simplified repeatable opportunity. It does not account for correlated positions, liquidity, existing exposure, or changing probabilities. The calculation is a model output, not a personal staking recommendation.
Frequently asked questions
Why does Kelly return zero?
If the estimated probability is no higher than the break-even probability, there is no positive modeled edge. The tool does not suggest a negative stake or automatically take the opposite side.
Why use fractional Kelly?
Scaling the model allocation down reduces stake size and volatility relative to full Kelly. It does not eliminate losses or make an inaccurate probability estimate reliable.