Free tool
Kelly Criterion Calculator
Work out the optimal stake for a bet from your bankroll, the odds and your estimated edge.
Kelly stake calculator
Recommended stake
$50.00
% of bankroll
5.00%
How the Kelly criterion works
Kelly sizes each bet as a percentage of your bankroll, scaled to your edge: the bigger the gap between your estimated probability and the odds, the larger the stake. The formula is(b·p − q) ÷ bwhere b = decimal odds − 1, p = your win probability and q = 1 − p.
Full Kelly grows a bankroll fastest in theory but swings hard and punishes over-confident estimates. Most bettors use half or quarter Kelly to cut the volatility.
Worked example
You estimate a 55% chance at odds of 2.00, bankroll $1,000.
b = 1.00, p = 0.55, q = 0.45 → full Kelly = (1×0.55 − 0.45) ÷ 1 = 10%.
Full Kelly stake = $100. Half Kelly = $50 — the more sensible bet given estimate uncertainty.
Frequently asked questions
What is the Kelly criterion?
The Kelly criterion is a formula that sets your stake as a fraction of your bankroll based on your edge and the odds. It maximises long-term bankroll growth while avoiding ruin. The formula is (b·p − q) ÷ b, where b = decimal odds − 1, p = your win probability and q = 1 − p.
Why use half or quarter Kelly?
Full Kelly is mathematically optimal but very volatile, and it is unforgiving if your probability estimate is too high. Betting a fraction — half or quarter Kelly — keeps most of the growth with far less variance, which is why most serious bettors use it.
What does a negative Kelly result mean?
A negative result means the bet has no positive expected value at those odds and probability, so Kelly recommends staking nothing. Only bet when your estimated probability is higher than the odds imply.