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Kelly Criterion Calculator

Optimal stake as a fraction of bankroll for a given edge.

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The fast lane for the math you almost remember from school. Type the numbers, get the answer, move on with your day.

Try a scenario

Click to load — tweak from there.

Inputs

Result

Recommended stake

$250.00

Full Kelly fraction

10.00%

Fraction of bankroll used

5.00%

Expected value per unit

10.00%

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How to use this

  1. 1Enter bankroll ($).
  2. 2Enter your win probability (%).
  3. 3Enter decimal odds offered.
  4. 4Enter kelly fraction used (%).
  5. 5Read your recommended stake on the right — it updates as you type.
  6. 6Hit Share to keep the scenario or send it to someone.

About this calculator

The Kelly formula sizes a position to maximize long-run growth. Enter your estimated win probability and the odds offered to see full Kelly, half Kelly, and the dollar stake.

Formulaf* = (bp − q) ÷ b, where b = decimal odds − 1, p = win probability, q = 1 − p.

Worked example

Using the values the calculator loads with:

Inputs

  • Bankroll: 5000 $
  • Your win probability: 55 %
  • Decimal odds offered: 2
  • Kelly fraction used: 50 %

Results

  • Recommended stake: $250.00
  • Full Kelly fraction: 10.00%
  • Fraction of bankroll used: 5.00%
  • Expected value per unit: 10.00%

What each field means

Inputs

Bankroll ($)
The bankroll used in the calculation, measured in $. Starts at 5000 $ so you have a working example on load.
Your win probability (%)
The your win probability used in the calculation, measured in %. Starts at 55 % so you have a working example on load. Accepted range: 0–100 %.
Decimal odds offered
The decimal odds offered used in the calculation. Starts at 2 so you have a working example on load.
Kelly fraction used (%)
The kelly fraction used used in the calculation, measured in %. Starts at 50 % so you have a working example on load. Accepted range: 5–100 %.

Results

Recommended stake
Returned as a money amount in US dollars and shown as the headline result. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
Full Kelly fraction
Returned as a percentage. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
Fraction of bankroll used
Returned as a percentage. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
Expected value per unit
Returned as a percentage. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.

FAQ

Why use half Kelly?

Full Kelly is brutally volatile and assumes your probability estimate is exact. Half Kelly keeps most of the growth with a fraction of the drawdown.

What if the result is negative?

You have no edge at those odds. The correct stake is zero.

Accuracy and limitations

  • Results are rounded for display; the underlying calculation keeps full precision.
  • Very large or very small inputs may hit floating-point limits in the browser.
  • Inputs outside the accepted range are clamped rather than rejected.

Cite this calculator

Writing about this topic? Grab a citation — every link helps keep these tools free.

APA
RevenueLab. (2026). Kelly Criterion Bet Size Calculator. Retrieved from https://www.revenuelab.fyi/toolbox/kelly-criterion
HTML
<p>Source: <a href="https://www.revenuelab.fyi/toolbox/kelly-criterion" target="_blank" rel="noopener">Kelly Criterion Bet Size Calculator — RevenueLab</a> (2026).</p>
Markdown
Source: [Kelly Criterion Bet Size Calculator — RevenueLab](https://www.revenuelab.fyi/toolbox/kelly-criterion) (2026).
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