Free betting tools
Kelly Criterion & Unit Size Calculator
Size your stake from your edge and bankroll with full or fractional Kelly.
Odds format
Kelly fraction
Enter valid odds and values to see the result.
Track these bets in your bankroll
Log stakes and see ROI, win rate and profit curves in My Bankroll.
Frequently asked questions
What is the Kelly criterion?
Kelly is a formula for stake sizing: f = (b × p − q) ÷ b, where b is decimal odds − 1, p is your win probability and q = 1 − p.
Why use half or quarter Kelly?
Full Kelly is very aggressive and sensitive to errors in your probability estimate. Fractional Kelly lowers swings while keeping most of the growth.
What is a betting unit?
A unit is a fixed share of your bankroll, often 1%. Betting in units keeps stakes consistent and makes results easy to compare.
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For information only. These calculators do not guarantee profit. 18+. Bet responsibly.