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Sports Betting EV Calculator & Kelly Bet Size
Enter the odds you can get and your own win probability. We show whether the bet is +EV, how big your edge is, and how much to stake with the Kelly criterion.
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| Breakeven | Edge | EV per bet | EV % |
|---|---|---|---|
| — | — | — | — |
| Full Kelly | Half Kelly | Quarter Kelly |
|---|---|---|
| — | — | — |
Runs in your browser. Math only, nothing stored.
How to use this calculator
Type the American odds you can bet, your honest estimate of the win probability (the no-vig price from a sharp book is a good starting point), your stake and your bankroll. The green line means +EV, red means −EV. The Kelly row suggests a stake size; most bettors use quarter or half Kelly. Copy the result to share the bet.
Why most bettors use fractional Kelly
Full Kelly maximizes long-run growth only if your win probability is exactly right. Overestimate it by a few points and full Kelly overbets badly, so half or quarter Kelly gives most of the growth with far smaller swings — the Kelly bankroll calculator shows the growth math. For DFS pick’em, see the Power vs Flex picker for EV at your hit rate. Line moves are one of the best signals that a price has value; check any game in the line movement checker.
FAQ
How is expected value calculated in sports betting?
EV = (win probability × profit if you win) − (loss probability × stake). At +150 with a 42% win chance, EV on $10 is 0.42 × $15 − 0.58 × $10 = +$0.50, a 5% return.
What is the Kelly criterion?
Kelly sizes a bet as edge ÷ net odds: f = (p × b − (1 − p)) ÷ b, where b is decimal odds minus 1. Most bettors use half or quarter Kelly because their win probabilities are estimates. The Kelly calculator goes deeper on bankroll and unit size.
Where does my win probability come from?
It is your estimate. A common reference is the no-vig probability from a sharp market: put both sides into the hold calculator or odds converter, then compare that fair number to the price you can get elsewhere.