Kelly criterion calculator: how much to bet
The Kelly criterion sizes a bet in proportion to its edge: the bigger the advantage, the larger the share of your bankroll. Enter the bankroll, the odds and the true win probability (or the fair odds): the calculator shows the full-Kelly share and the stake for full, half or quarter Kelly. With no edge, Kelly says not to bet.
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How to use the calculator
- 1
Enter your bankroll
The money set aside for betting, not your savings.
- 2
Enter odds and true chance
The price offered and the fair odds or the win probability you estimate.
- 3
Choose the Kelly fraction
Full Kelly grows the bankroll fastest but swings hard; half or quarter Kelly is what most bettors use.
Worked example
Bankroll $1,000, odds +110 (2.10), true chance 51.22% (fair -105). Full Kelly = (1.10 x 0.5122 - 0.4878) / 1.10 = 6.88% of the bankroll, a $68.75 stake. Half Kelly bets $34.38, quarter Kelly $17.19.
Related calculators
- EV calculator Expected profit in dollars and percent, from your odds and the fair odds.
- No-vig calculator Measure the vig of any market and strip it out to get the fair odds.
- Odds converter American, decimal, fractional odds and implied probability, converted both ways.
- Dutching calculator Split a stake across outcomes so any of them pays the same.
Frequently asked questions
What is the Kelly criterion?
A formula published by John Kelly in 1956 that gives the stake maximizing the long-run growth of a bankroll, given the odds and the probability of winning.
Why use half or quarter Kelly?
Full Kelly assumes your probability is exactly right. Estimates never are, and full Kelly on an overestimated edge overbets. Fractional Kelly keeps most of the growth with far smaller swings.
What if the calculator says no edge?
The odds are at or below the fair price, so any stake has negative or zero expected value. Kelly's answer is to bet nothing.
Should I recalculate the stake after every bet?
Yes, Kelly is a share of the current bankroll: it grows after wins and shrinks after losses, which is what protects you from going broke.
Can I use Kelly for parlays?
Yes, with the parlay's total odds and its true probability (the product of the legs' probabilities). The stakes come out small, because parlays win rarely.
By the NinjaBet Editorial Team Updated on October 28, 2026
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