Kelly Criterion Calculator

Enter your bankroll, the odds and your win probability to see how much to bet with full, half or quarter Kelly. Free, no sign-up.

The Kelly criterion formula

The Kelly criterion gives the share of your bankroll to bet so that your bankroll grows as fast as possible over the long run, when you have an edge:

Kelly % = (b × p − q) ÷ b

b is the net decimal odds (decimal odds − 1), p your win probability and q = 1 − p. If the result is zero or negative, you have no edge and the Kelly bet is zero.

Example: +100 with a 55% chance

b = 1, p = 0.55, q = 0.45. Kelly = (1 × 0.55 − 0.45) ÷ 1 = 10% of your bankroll. With $1,000, full Kelly is a $100 bet and half Kelly a $50 bet.

Why most bettors use a fraction of Kelly

Full Kelly assumes your win probability is exactly right. In practice it is an estimate, and an error makes full Kelly bets too big and the swings very large. That is why many bettors use half or quarter Kelly, or a flat stake. On Odyn, many members use 1 to 2% of their betting bankroll and keep it fixed.

To check whether a bet has an edge at all, compare its odds with the fair odds from the no-vig calculator.

FAQ

What is the Kelly criterion in sports betting?

A formula that gives the share of your bankroll to bet on a wager with positive expected value, so that the bankroll grows as fast as possible over the long run.

How much should I bet with the Kelly criterion?

Kelly % = (b × p − q) / b, where b is the decimal odds minus 1, p your win probability and q = 1 − p. At +100 with a 55% chance, full Kelly is 10% of your bankroll.

Is half Kelly better than full Kelly?

Half Kelly grows the bankroll a bit more slowly but with much smaller swings, and it is more forgiving when your win probability is overestimated. Most bettors who use Kelly use a fraction of it.

What if the Kelly result is negative?

Then the bet has no edge at those odds and the Kelly stake is zero: the formula says not to bet.

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