Kelly Criterion Calculator
Free · No signup · Works in your browser
Work out the mathematically optimal stake for a bet you believe has an edge. Enter your bankroll, your own estimate of the win probability, and the decimal odds on offer. It returns full, half and quarter Kelly — and tells you to stake nothing if there's no edge.
Enter your bankroll, probability and odds to see the stake.
How the Kelly stake is worked out
The Kelly fraction of your bankroll to stake is:
f = (b × p − q) ÷ b, where b = decimal odds − 1, p = your win probability, q = 1 − p.
Example: a 55% chance (p = 0.55) at odds of 2.00 gives b = 1, so f = (1 × 0.55 − 0.45) ÷ 1 = 0.10 — full Kelly is 10% of bankroll, or $100 on a $1,000 roll. Half-Kelly (the sane default) is $50. If the numerator b × p − q is zero or negative, there's no edge and the stake is zero.
The honest catch
Kelly is a sizing tool, not an edge tool: it assumes your probability is accurate, and it never quite is. Overstate your edge and full Kelly tells you to bet too much — which is how bankrolls bust. That's why almost everyone uses half- or quarter-Kelly. Read the full method in our Kelly criterion guide, and see why an edge is so hard to get in the value betting guide.
Calculations are exact from the numbers you enter. This tool is for information only and assumes a single bet paying out at the stated decimal odds; it ignores commissions and correlations between bets.
Related guides & tools
- Kelly criterion staking explained — the formula and why half-Kelly wins.
- Bankroll management & staking — flat and percentage staking, the safer defaults.
- Value betting explained — the edge Kelly needs as its input.
- Margin & Fair Odds Calculator — get a fair-odds baseline for your probability.