Kelly Criterion calculator
Enter your bankroll, the odds and your own estimate of the chance the bet wins. The calculator shows the Kelly stake and the expected value on your numbers.
Written by BettingSeeker Editorial Team
How the Kelly Criterion works
Kelly compares your estimated chance of winning with the chance implied by the odds. If you think the bet is more likely to win than the odds suggest, it recommends staking a share of your bankroll that grows with the size of that gap. If you do not see an edge, it recommends no bet at all.
The weak point is the input. A few percentage points of overconfidence can turn a small, sensible stake into a large one, which is why many people who use Kelly bet a fraction of it. Betting is not a reliable way to make money, and no staking formula changes that.
Worked example
A 1,000 bankroll, odds of 6/5 (2.20) and an estimated 50% chance of winning:
- Implied probability: 1 ÷ 2.20 = 45.45%, so your estimated edge is 4.55 percentage points
- Kelly fraction: (0.50 × 2.20 − 1) ÷ (2.20 − 1) = 0.10 ÷ 1.20 = 8.33%
- Full Kelly stake: 83.33; half Kelly 41.67; quarter Kelly 20.83
- Expected value: 0.50 × 2.20 − 1 = +0.10 per 1 staked, if your 50% estimate is right
The formula
Using decimal odds D and your probability p: Kelly fraction f = (p × D − 1) ÷ (D − 1). Stake = f × bankroll. If f is zero or negative, there is no bet. Expected value per unit staked = p × D − 1.
Frequently asked questions
What is the Kelly Criterion?
It is a formula for sizing a bet as a share of your bankroll, based on the odds and your own estimate of the chance of winning. It only suggests a stake when your estimate is higher than the probability implied by the odds.
Why use half or quarter Kelly?
Full Kelly assumes your probability estimate is exactly right, which it never is. Overestimating your edge with full Kelly leads to large swings and can wipe out a bankroll. Fractional Kelly cuts the stake, and the risk, at the cost of slower growth if your edge is real.
What does it mean if the calculator says no bet?
Your estimated probability is at or below the implied probability of the odds, so on your own numbers the bet has no edge. Kelly suggests staking nothing.
Can the Kelly Criterion make betting profitable?
No. It only sizes bets; it cannot create an edge. Bookmaker odds include a margin, and most bettors' estimates are not more accurate than the market, so for most people the long-run result of betting is a loss whatever staking plan they use.