Kelly Criterion Calculator

How to use it

1. 1 Enter your bankroll and the odds you can bet at.
2. 2 Enter your own estimated chance of winning, as a percentage.
3. 3 Pick full, half, quarter or a custom fraction of Kelly. Half or less is common.
4. 4 Read the recommended stake. If there is no edge, the result is a $0 stake.

What the Kelly Criterion does

Kelly finds the share of your bankroll to bet that maximises long-run growth, given the odds and the probability that you win. The bigger your edge, the larger the stake; with no edge, the answer is not to bet at all.

Kelly is only as good as the probability you give it. If your estimate is too high, it will tell you to bet more than you should, and overbetting hurts a bankroll quickly. Most bettors use a fraction of Kelly (half or quarter) to leave room for estimation error and to smooth out swings.

The formula

With b as the decimal odds minus 1 (the profit per $1 staked), p as your win probability and q as 1 minus p, the full Kelly fraction is f* = (b x p - q) / b. The recommended stake is your bankroll times f* times the fraction of Kelly you choose.

If f* is zero or negative, the bet has no edge at those odds. The calculator shows "No bet" and a $0 stake instead of a negative number. The edge shown is the expected profit per $1 staked, which is p x decimal odds minus 1.

Worked example

Your bankroll is $1,000 and you can bet +110 (decimal 2.10, so b = 1.10). You estimate a 55% chance of winning. The edge is 15.50% per dollar staked.

Full Kelly is (1.10 x 0.55 - 0.45) / 1.10, which is 14.09% of bankroll, or $140.91. At half Kelly the stake is $70.45, which is 7.05% of the bankroll.

The formula

Frequently asked questions