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Kelly Criterion Calculator

Estimate an aggressive theoretical allocation fraction.

No signupInstant calculationEducational use
01

Enter your assumptions

Adjust any value and the calculation updates instantly in your browser.

Live calculation mapRisk
Win rate (%)55
Average win/loss ratio1.5

Visual proportions are provided for quick comparison only; the result cards use the exact values entered.

02

Your calculated results

Review the estimate and the explanation shown below each result.

◎Full Kelly estimate25%Updates instantly
↕Half Kelly reference12.5%Updates instantly
▦Quarter Kelly reference6.25%Updates instantly
ⓘ Results are educational estimates. Real trading outcomes can differ because of fees, spread, slippage, taxes, liquidity and execution behavior.

What is a Kelly Criterion Calculator?

The Kelly criterion estimates a theoretical fraction of capital based on win probability and payoff ratio. Full Kelly can be highly volatile, so many risk managers use a smaller fraction or another fixed-risk method.

Formula

Kelly fraction = Win probability − (Loss probability ÷ Win/loss ratio)

Example calculation

With a 55% win probability and a 1.5 average win/loss ratio, the theoretical Kelly fraction is 25% before practical risk reductions.

How to use this tool responsibly

  • Treat full Kelly as aggressive.
  • Use reliable inputs.
  • Never confuse an estimate with a guarantee.

Frequently asked questions

Is this tool free?

Yes. This tool is free to use and does not require an account.

Does this tool provide financial advice?

No. Results are educational estimates, not financial, investment, tax, or legal advice.

Are fees and slippage included?

Only when the calculator provides an input for them. Real results may differ because of spread, slippage, commissions, taxes, and execution quality.

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Important disclaimer

This tool is for education and planning only. It does not provide financial advice or guarantee any result. Market orders, stop orders and limit orders may execute differently from estimates because of liquidity, volatility, spread, slippage and platform behavior.