The Kelly Calculator recommends how much to stake based on your edge (EV), the odds, and your bankroll. It aims to maximize long-term growth while controlling risk. Use the Kelly multiplier (e.g., 0.5 for Half-Kelly, 0.25 for Quarter-Kelly) to dial back volatility.
A Kelly criterion calculator tells you how much of your bankroll to stake on a bet with positive expected value. Enter the bet's EV %, its decimal odds, a Kelly multiplier and your bankroll, and the calculator returns the amount to wager.
The Kelly criterion is a staking formula that sizes each bet as a fraction of your bankroll in proportion to your edge. Staking this way maximises the long-run growth of the bankroll when your probability estimates are correct. It never recommends staking on a bet with zero or negative expected value.
The calculator uses the Kelly formula written in terms of expected value:
Full Kelly fraction = EV ÷ (decimal odds − 1)
Stake = bankroll × Kelly multiplier × EV ÷ (decimal odds − 1)
EV (as a decimal) = true probability × decimal odds − 1This is equivalent to the classic form f = (bp − q) ÷ b, where b is the decimal odds minus 1, p the probability of winning and q = 1 − p.
A bet at decimal odds of 2.10 with 5% EV (a 50% chance of winning) and a bankroll of $1,000:
| Kelly multiplier | Stake | Share of bankroll |
|---|---|---|
| 1 (full Kelly) | $45.45 | 4.55% |
| 0.5 (half Kelly) | $22.73 | 2.27% |
| 0.25 (quarter Kelly) | $11.36 | 1.14% |
Full Kelly assumes your probability estimate is exact. In practice estimates contain errors, and staking full Kelly on an overestimated edge means overbetting, which causes large drawdowns. A multiplier of 0.5 (half Kelly) or 0.25 (quarter Kelly) gives up some long-run growth for much lower volatility: in the standard model, half Kelly keeps roughly three quarters of full Kelly's growth rate with about half the volatility.
The calculator only accepts a positive EV: if EV is zero or negative, Kelly's answer is not to bet.
Convert the share price to decimal odds with 1 ÷ price. A share at 0.40 is 2.50 in decimal odds. If you estimate a 45% chance, EV = 0.45 × 2.50 − 1 = 12.5%, and full Kelly is 12.5% ÷ 1.50 = 8.33% of your bankroll: $83.33 on $1,000, or $20.83 at quarter Kelly. Fees, spreads and settlement rules reduce the real edge, so a smaller multiplier is safer.
A multiplier of 1 is full Kelly. Many bettors use 0.25 to 0.5 because their probability estimates are uncertain; a lower multiplier reduces drawdowns at the cost of slower growth.
Yes. Kelly maximises long-run growth when your edge is real, but individual bets still lose, and an overestimated edge leads to overbetting. Kelly also assumes you reinvest winnings and bet repeatedly.
Kelly recommends no bet. The calculator requires a positive EV %.
Simultaneous bets draw on the same bankroll, so staking full Kelly on each can commit too much of it. Reduce the stakes, for example with a lower multiplier, when several bets run at the same time.