Kelly criterion calculator
The Kelly criterion sizes each bet by its edge: bigger when the price beats your estimate by more, nothing when it doesn't. Enter the odds, your fair odds and your bankroll.
The Kelly formula
Kelly fraction = (chance × decimal odds − 1) / (decimal odds − 1)
It's the stake that grows a bankroll fastest over the long run if your chances are right. If they're wrong, full Kelly overbets, which is why the calculator defaults to a quarter Kelly.
Worked example
The book pays +150 (2.50) and your fair odds are +130 (a 43.48% chance). Kelly = (0.4348 × 2.50 − 1) / 1.50 = 5.80% of your bankroll. On $1,000:
| Fraction | Share | Stake on $1,000 |
|---|---|---|
| Full Kelly | 5.80% | $57.97 |
| 1/2 Kelly | 2.90% | $28.99 |
| 1/4 Kelly | 1.45% | $14.49 |
| 1/10 Kelly | 0.58% | $5.80 |
Why fractional Kelly
Fair odds are estimates. Halving the stake costs only about a quarter of the long-run growth but cuts the swings a lot, and it protects you when an estimate is off. Bets placed at the same time on the same game also share risk. The daily plan sets bets, books and amounts from your bankroll.
Questions
What is the Kelly criterion in betting?
A formula for the stake that maximises long-run bankroll growth: the edge divided by the net odds, (chance x decimal odds - 1) / (decimal odds - 1).
Should I bet full Kelly?
Most bettors don't. Full Kelly assumes your win chances are exact; with estimated chances it overbets. Quarter to half Kelly is common.
What if Kelly says 0?
Then the bet isn't +EV at your fair odds, and Kelly says not to bet.
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Updated 2026-10-26