Kelly Criterion Calculator
Size each bet in proportion to your edge. Enter your bankroll, the odds, and your fair win probability, and the calculator returns the Kelly stake plus safer fractional versions.
Example numbers are pre-filled. Replace them with the prices in front of you.
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How to use the Kelly calculator
- Enter your bankroll. Use only money set aside for betting.
- Enter the odds you can bet and either your win probability or the fair odds from a devigged sharp line.
- Pick a Kelly fraction. Quarter Kelly is a sensible default for bettors using market-derived edges.
If the calculator says No bet, your probability doesn’t beat the break-even rate at that price, and Kelly stakes nothing.
The formula
Worked example
Bankroll $5,000. You can bet +110 (b = 1.10) on a side you rate at a 50% win probability.
- Full Kelly: (1.10 × 0.50 − 0.50) ÷ 1.10 = 4.55%, or $227.27.
- Quarter Kelly: 1.14%, or $56.82.
The edge here is 5% (0.50 × 2.10 − 1). A smaller edge or a less certain probability should mean a smaller stake, and Kelly scales it down automatically.
Get +EV bets flagged against sharp prices
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Start the $1 ProfitDuel trialAffiliate link. The $1, 3-day trial applies to ProfitDuel's Starter plan as listed in September 2026. 21+ and in states where online sports betting is legal.Frequently asked questions
Why not bet full Kelly?
Full Kelly assumes your win probability is exactly right. It never is. Overestimating your edge with full Kelly means overbetting, which cuts long-run growth and makes drawdowns of 50% or more routine. Most professionals bet a quarter to half Kelly.
What does expected growth per bet mean?
It’s the average percentage your bankroll grows per bet if you stake this fraction repeatedly on bets like this one, measured geometrically. It’s usually a fraction of a percent, which is why volume matters.
Should I use Kelly for arbitrage or bonus bets?
No. Arbitrage and hedged promos have no outcome risk, so Kelly doesn’t apply. Size those by the promo limit or the book’s max bet. Kelly is for unhedged +EV bets.