Kelly vs Fixed Fraction Calculator
Compare full Kelly, half Kelly and your planned fixed fraction from win rate, payoff ratio and the fixed fraction.
Results
Fill in the inputs and click Calculate.
- Full Kelly
- –
- Half Kelly
- –
- Full Kelly − Fixed
- –
Risk disclaimer
This calculator provides a mathematical reference only, not investment advice. Kelly is highly sensitive to estimates.
Why compare fixed fractions with Kelly?
Full Kelly targets fastest theoretical growth but is volatile; half Kelly (halving the result) balances growth and drawdown and is common in practice.
A fixed fraction (e.g. 10% each time) is simple to run; the delta column shows whether you are under or over Kelly.
How to use
- Enter the win rate in percent and the payoff ratio.
- Enter your planned fixed position fraction in percent.
- Click Calculate to compare full Kelly, half Kelly and the delta.
Formula
- f = (Payoff × WinRate − (1−WinRate)) ÷ Payoff
- Half Kelly = f ÷ 2
- Delta = Full Kelly − Fixed Fraction
Example
50% win rate, payoff 2: full Kelly 25%, half Kelly 12.5%.
A fixed 10% sits 15 pp below full Kelly and close to half Kelly.
FAQ
What does a negative delta mean?
Fixed fraction below full Kelly (more conservative); a large positive means betting above full Kelly (not advised).
Which one should I use?
Without confident estimates, prefer half Kelly or a lower fixed fraction; never exceed full Kelly.