Kelly criterion calculator

The Kelly formula maximises long-term bankroll growth by sizing stakes to your true edge.

Decimal odds offered

Your true win probability (0–1)

Bankroll (£)

Edge

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Full Kelly

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Half Kelly

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Quarter Kelly

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Enter odds, probability and bankroll.

How to use this calculator

Enter the decimal odds offered (e.g. 2.50).
Enter your estimated probability of winning (e.g. 0.45 for 45%).
Enter your bankroll.
The recommended stake (full Kelly) and half-Kelly appear instantly.

Worked example

Odds 2.50, true probability 0.45, bankroll £1,000. Edge = 0.45 × 2.50 - 1 = 0.125. Kelly fraction = 0.125 / (2.50-1) = 8.33% = £83 full Kelly, £41 half-Kelly.

Common questions

Should I use full Kelly?

No. Most professionals use half or quarter Kelly. Full Kelly maximises growth in theory but is too volatile in practice — and your edge estimates are never perfect.

What if Kelly is negative?

Negative Kelly means the bet has no value. Do not place it.