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Kelly Criterion Calculator: Bet Sizing for Sports Betting
Enter the odds, your win probability and your bankroll to see the Kelly stake as a fraction, a percentage and a dollar amount, at full, half or quarter Kelly.
What is a Kelly criterion calculator?
A Kelly criterion calculator tells you what share of your bankroll to bet, based on the odds and your estimate of the win probability. It applies the Kelly formula, (b × p - q) / b, and returns the Kelly fraction, the same fraction as a percentage, the dollar stake for your bankroll at full, half or quarter Kelly, and the decimal odds. The result is only as good as the probability you enter.
Why use a Kelly criterion calculator?
- Size a bet from the odds and your win probability
- See the Kelly stake as a fraction, a percentage and a dollar amount
- Bet half or quarter Kelly to lower the swings in your bankroll
- See when the odds leave no edge and Kelly is zero
- Compare stakes across different probability estimates
How to use the Kelly calculator
- 1Choose the odds format you have, such as American (-110) or decimal (1.91)
- 2Enter the odds
- 3Enter your win probability as a percentage
- 4Enter your bankroll
- 5Choose full, half or quarter Kelly
- 6Read the Kelly fraction, percentage and stake
Example: +110 with a 55% win probability
At +110 the decimal odds are 2.10, so b = 1.1. With p = 0.55 and q = 0.45, Kelly = (1.1 × 0.55 - 0.45) / 1.1 = 0.1409, or 14.09% of your bankroll. With a $1,000 bankroll that is $140.91. Half Kelly is 7.05% ($70.45) and quarter Kelly is 3.52% ($35.23).
How to calculate the Kelly criterion
Convert the odds to decimal and subtract 1 to get b. At -110, b = 0.9091; at +150, b = 1.5.
Kelly fraction = (b × p - q) / b, with p your win probability and q = 1 - p.
Stake = Kelly fraction × bankroll. A fraction of zero or below means there is no edge at those odds, and the calculator returns 0.
Kelly stakes at -110
The full Kelly stake for a -110 bet at different win probabilities, with a $1,000 bankroll. The break-even probability at -110 is 52.38%.
- 52%: 0.00%, $0.00
- 53%: 1.30%, $13.00
- 55%: 5.50%, $55.00
- 57%: 9.70%, $97.00
- 60%: 16.00%, $160.00
Full, half and quarter Kelly at +110
Half and quarter Kelly bet a set share of the full Kelly stake. The stake for a +110 bet at different win probabilities, with a $1,000 bankroll. The break-even probability at +110 is 47.62%.
| Win probability | Full Kelly | Half Kelly | Quarter Kelly |
|---|---|---|---|
| 50% | 4.55% ($45.45) | 2.27% ($22.73) | 1.14% ($11.36) |
| 52% | 8.36% ($83.64) | 4.18% ($41.82) | 2.09% ($20.91) |
| 55% | 14.09% ($140.91) | 7.05% ($70.45) | 3.52% ($35.23) |
| 58% | 19.82% ($198.18) | 9.91% ($99.09) | 4.95% ($49.55) |
| 60% | 23.64% ($236.36) | 11.82% ($118.18) | 5.91% ($59.09) |
Kelly Criterion FAQ
Understanding Kelly
Kelly fraction = (b × p - q) / b, where b is the decimal odds minus 1, p is your win probability and q = 1 - p. At +110 (2.10 decimal) with a 55% win probability, b = 1.1 and q = 0.45, so Kelly = (1.1 × 0.55 - 0.45) / 1.1 = 14.09% of your bankroll.