Kelly Criterion Calculator
Calculate the Kelly optimal stake for a bet with a known edge.
About Kelly Criterion Calculator
Kelly maximises long-run growth but produces uncomfortable volatility, and it recommends zero when there is no edge. Half Kelly gives three quarters of the growth with far smaller drawdowns. Kelly is acutely sensitive to probability estimation error, which is why practitioners use a fraction rather than the full figure.
Formula
Kelly Criterion
Kelly fraction = (probability × net odds − losing probability) ÷ net odds
- full Kelly
- The stake maximising long-run logarithmic growth
- fractional Kelly
- A smaller share, trading growth for lower volatility
Worked example
With the default values below, Kelly Criterion Calculator returns Recommended Stake of $208.33. Change any input above and every figure here is recalculated in your browser.
Inputs used
- Your estimated win probabilityaccepts 0–100 %
- 45 %
- Decimal odds offeredaccepts 1.01–1,000
- 2.5
- Bankrollminimum 0
- 5,000
- Fraction of full Kelly to useaccepts 0–100 %
- 50 %
Results
- Recommended Stake
- $208.33
- Full Kelly Stake as a Share of Bankroll
- 8.333%
- Fractional Kelly Share of Bankroll
- 4.167%
- Edge Over the Implied Probability
- 5.000%
- Verdict
- Stake sizing is within a reasonable range
Step by step
- 1Values used
- 2Kelly Criterion
- 3Recommended Stake= 208.33
- 4Full Kelly Stake as a Share of Bankroll= 8.333
- 5Fractional Kelly Share of Bankroll= 4.167
- 6Edge Over the Implied Probability= 5.000
- 7Verdict= Stake sizing is within a reasonable range
Assumptions and limits
- The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
- In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
- Figures are rounded for display to 3 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
- These figures are estimates based on population-average formulas and are intended for training and recreational planning only. They are not medical advice. Consult a qualified health professional before starting or changing an exercise programme, particularly if you have an existing medical condition.
- This is an estimate for general information and not professional medical advice. See the full disclaimer for the limits that apply to this kind of calculator.
How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.
These figures are estimates based on population-average formulas and are intended for training and recreational planning only. They are not medical advice. Consult a qualified health professional before starting or changing an exercise programme, particularly if you have an existing medical condition.
Frequently Asked Questions
How is Kelly Criterion calculated?
Kelly fraction = (probability × net odds − losing probability) ÷ net odds Kelly maximises long-run growth but produces uncomfortable volatility, and it recommends zero when there is no edge. Half Kelly gives three quarters of the growth with far smaller drawdowns.
Why does Kelly Criterion matter?
Kelly is acutely sensitive to probability estimation error, which is why practitioners use a fraction rather than the full figure.
What values do I need to enter?
This calculator takes 4 inputs: Your estimated win probability, Decimal odds offered, Bankroll, Fraction of full Kelly to use. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.