Kelly Criterion Calculator
Enter the target odds and the fair odds (from the Fair Odds calculator) to get the optimal stake for your bankroll.
The odds offered by your bookmaker
From your Fair Odds calculator
Your total capital dedicated to betting
Full Kelly
Maximum growth, high risk
Half Kelly
Recommended for value betting
Quarter Kelly
Conservative, low variance
Calculation details
Understanding the Kelly criterion
The problem Kelly solves
You have identified a +EV bet. But how much should you stake? Too little and you underexploit your edge. Too much and a bad run can wipe you out before the law of large numbers works in your favor. Kelly answers exactly that question.
The formula
Kelly computes the optimal fraction of your bankroll to stake in order to maximize the geometric growth of your capital over the long run. It depends on two parameters: your mathematical edge (EV) and the net profit if you win.
Why half Kelly is recommended
Full Kelly is mathematically optimal but assumes your estimate of the fair odds is perfect, which is never the case. In practice, value bettors use half Kelly: it keeps 75% of full Kelly's theoretical growth while cutting variance in half and drastically reducing the risk of ruin.
Quarter Kelly to start out right
If you are just starting out or have a low tolerance for variance, quarter Kelly is advised. You stake 25% of the optimal amount, growth is slower, but losing streaks remain psychologically manageable and let you stay in the game over time.
Strategy comparison
| Strategy | Stake | Growth | Variance | Who is it for? |
|---|---|---|---|---|
| Full Kelly | f* | 100% | Very high | Experienced trader |
| Half Kelly | f*/2 | ~75% | Moderate | Active value bettor |
| Quarter Kelly | f*/4 | ~50% | Low | Beginner |
Frequently asked questions
What is the Kelly criterion?
A mathematical formula that determines the optimal fraction of your bankroll to stake on a bet, based on your edge (the gap between the offered odds and the fair odds). It maximizes bankroll growth over the long run.
How do you calculate the Kelly stake for a sports bet?
The formula uses the true probability of winning (derived from the fair odds) and the net profit per unit staked (the odds minus one). The calculator does the math automatically from the target odds, the fair odds and your bankroll.
Why stake half Kelly or quarter Kelly?
Full Kelly maximizes growth in theory, but assumes your fair odds estimate is perfect. In practice, a fraction (half or quarter) sharply reduces variance and protects against estimation errors: quarter Kelly is the recommended standard when starting out in value betting.
Is the Kelly calculator free?
Yes, free and with no account: the calculation runs in your browser and no data is sent.