Kelly criterion calculator
The Kelly criterion sizes each bet as a share of your bankroll in proportion to your edge: f = (b·p − q) ÷ b. Bigger edge, bigger stake; no edge, no bet.
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Updated 19 October 2026 · Free, no sign-up. All calculations run in your browser. 18+ · Play responsibly.
How it works
- Enter the odds and your estimate of the win probability.
- Enter your bankroll and pick a Kelly fraction.
- The stake grows with your edge and is zero when there is no edge.
The formula
f* = (b × p − (1 − p)) ÷ b, where b = odds − 1. Stake = f* × fraction × bankroll.
Worked example
Odds 2.20, win probability 50%: b = 1.2, f* = (1.2 × 0.5 − 0.5) ÷ 1.2 = 8.33%. With quarter Kelly and a €1,000 bankroll the stake is €20.83.
Why most bettors use a fraction
Full Kelly is only optimal if your probabilities are exactly right. Estimates are never perfect, so half or quarter Kelly keeps most of the growth with far smaller swings.
FAQ
What if Kelly says 0%?
The price has no edge for the probability you entered, so the calculator suggests not betting.