Kelly Criterion Calculator for Sports Betting
Enter the price, your estimate of the true win probability and your bankroll. The calculator returns the Kelly stake, as a full, half or quarter Kelly bet.
Kelly calculator
- Bet size
- $25.00
- % of bankroll
- 2.50%
- Full Kelly
- 10.00%
- Edge (EV %)
- +10.00%
Kelly is only as good as your probability. Most bettors use a fraction (half or quarter Kelly) because an overestimated edge makes full Kelly far too aggressive.
How to use it
- Enter the price you can bet and the true win probability, or switch to “No-vig odds” and enter the no-vig price.
- Enter your bankroll: the money set aside only for betting.
- Pick a fraction. Quarter Kelly is a common, cautious choice.
The math
f = (b × p − q) / b · b = decimal − 1 · q = 1 − p
stake = bankroll × f × fraction (0 when f ≤ 0)
Kelly sizing depends entirely on the probability you put in. The most reliable estimate for most bettors is the no-vig price; check yours with the EV calculator or see live +EV prices on the +EV page.
Frequently asked questions
What is the Kelly criterion?
A formula for how much of your bankroll to stake on a bet with an edge so that your bankroll grows as fast as possible over the long run. It stakes more when the edge is bigger and nothing when there is no edge.
What is the Kelly formula for sports betting?
f = (b × p − q) / b, where b is the decimal odds minus 1, p is the true win probability and q = 1 − p. At +100 (b = 1) with a 55% chance: (0.55 − 0.45) / 1 = 10% of your bankroll.
Why use half or quarter Kelly?
Full Kelly assumes your probability is exactly right. Real estimates are noisy, and overestimating the edge with full Kelly leads to large swings and drawdowns. Fractional Kelly gives up a little growth for much lower risk, which is why most bettors use it.
What does it mean when Kelly says to bet nothing?
The price is not +EV at the probability you entered: it pays less than the chance deserves. The Kelly stake is zero for any bet without an edge.
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