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Kelly Criterion Calculator
Calculate the bankroll fraction that maximizes expected logarithmic growth for a repeated binary payoff model.
No account to calculateNo real-money wageringTransparent assumptions
CALCULATOR
Kelly criterion
Calculate a model's growth-optimal stake and compare it with a smaller fractional stake.
Start with your assumptions
Enter values and calculate to see the result, method, and assumptions.
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Worked example
- Full Kelly fraction
- 10.0000%
- Half Kelly fraction
- 5.0000%
At 55% win probability and net profit odds of 1:1, full Kelly is 0.55 − 0.45/1 = 10%. Applying a half-Kelly multiplier gives 5% of bankroll. This result assumes the supplied odds are correct.
Example inputs
- winProbability:
0.55 - profitOdds:
1 - fractionalKelly:
0.5
Method
For net win odds b and win probability p, f* = p − (1 − p)/b. This tool restricts the allocation to the interval from zero to one, without shorting or borrowing. Fractional Kelly multiplies that allocation by a user-selected fraction.
Assumptions
The classical result assumes a repeatable payoff model with known probabilities and an objective of maximizing expected log wealth. Estimated edges can be wrong. A Kelly fraction is not a guarantee of profit, a maximum drawdown bound or a complete portfolio allocation rule.
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