Kelly criterion calculator
Enter your bankroll, the price, and your win probability to see the bet size that grows your bankroll fastest — plus the safer fractional-Kelly stakes most bettors actually use.
- Full Kelly fraction
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- Full Kelly stake
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| Strategy | % of bankroll | Stake | Profit if it wins |
|---|---|---|---|
| Quarter Kelly Most conservative | — | — | — |
| Half Kelly Common default | — | — | — |
| Three-quarter Kelly Aggressive | — | — | — |
| Full Kelly Maximum growth, max swings | — | — | — |
Lower fractions stake less and shrink your drawdowns; full Kelly grows the bankroll fastest but produces the wildest swings. Most disciplined bettors live between quarter and half Kelly.
Sizing bets the Kelly way
The Kelly criterion answers a question flat staking can’t: given a real edge, how much should you actually risk? Bet too little and your bankroll crawls; bet too much and a normal losing streak can wipe you out. Kelly finds the fraction that maximises long-run growth, scaling your stake up when the edge is large and down when it’s thin.
In practice the formula is unforgiving of bad inputs, so pair it with a sound staking plan from the bankroll management guide and confirm your bet is actually +EV first with the EV calculator. A small, honest edge bet at a fraction of Kelly beats a big stake on a number you can’t defend.
Frequently asked questions
- What is the Kelly criterion?
- The Kelly criterion is a formula for sizing bets to maximise the long-term growth rate of your bankroll. It stakes a percentage of your bankroll equal to your edge divided by the net odds: f* = (decimal × probability − 1) ÷ (decimal − 1). Bet that fraction and, given an accurate probability, your bankroll grows as fast as mathematically possible without risking ruin.
- Why do most bettors use fractional Kelly?
- Full Kelly is optimal only if your probability estimate is exactly right — and it almost never is. Overestimating your edge makes full Kelly badly oversized, producing brutal drawdowns. Betting a fraction (commonly a half or a quarter) keeps most of the growth while cutting volatility sharply, which is why the table above breaks out quarter, half, and three-quarter Kelly.
- What happens if I bet more than Kelly suggests?
- Staking above the full-Kelly fraction lowers your long-term growth rate and increases the risk of a deep drawdown; bet far enough past it and your expected growth turns negative even on a +EV bet. Kelly marks the ceiling — there is never a long-term reason to stake more than full Kelly, and usually good reason to stake less.
- Can the recommended Kelly stake be zero or negative?
- Yes. If the odds and your probability produce a negative edge, the formula returns a negative fraction, which means the correct stake is zero — don’t bet. A non-positive result here is the calculator telling you the price is -EV, so there is no bankroll-growing bet to be made at that number.
For informational purposes only. Not betting or financial advice. Please gamble responsibly. 21+ where applicable.