Kelly Criterion Calculator

Find the share of your bankroll the Kelly criterion says to stake on a bet with an edge. The Kelly criterion calculator shows full, half, and quarter Kelly.

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Kelly stake
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Estimate only. Not financial advice.

How to use the Kelly Criterion Calculator

  1. Enter your Win probability in percent.
  2. Enter the Odds and pick the format: net, decimal, or American. Add your Bankroll to see amounts.
  3. Press Calculate. The Kelly stake appears as a share of your bankroll, with half and quarter Kelly.

How it works

f* = p − (1 − p) ÷ b
b from decimal odds = decimal − 1
b from American odds = odds ÷ 100 (positive) or 100 ÷ |odds| (negative)
  • f*: the fraction of your bankroll to stake
  • p: the chance of winning
  • b: the net profit per 1 staked if you win

A zero or negative result means the bet has no edge at those odds.

Examples

  • A 60% chance at even money (b = 1): 0.6 − 0.4 ÷ 1 = 20% of the bankroll.
  • A 50% chance at 2-to-1 (b = 2): 0.5 − 0.5 ÷ 2 = 25%.
  • A 40% chance at even money: −20%, so the answer is don't bet.

Why many people bet half Kelly

Kelly maximizes long-run growth only if your probability is exactly right. Overestimate it and full Kelly can cause deep losses. Half Kelly gives up a little growth for much smaller swings, which is why professional bettors and investors often use a fraction.

Limitations

  • The result is only as good as your probability estimate.
  • Assumes independent bets and that you can stake any fraction.
  • For education only. Gambling carries a risk of losing money.

Frequently asked questions

What is the Kelly criterion?

A formula from 1956 that gives the stake size which grows a bankroll fastest over many bets, given an edge.

What does a negative Kelly mean?

That the odds do not pay enough for your chance of winning. The best stake is zero.

How do I convert decimal odds?

Subtract 1. Decimal odds of 2.50 mean b = 1.5.

Often used together with the Kelly Criterion Calculator.