Kelly Criterion Calculator & Bankroll Percentage Stake

This Kelly criterion calculator works out two things: the stake for a fixed percentage of your bankroll and the fraction the Kelly criterion suggests for your estimated probability and decimal odds.

Kelly criterion and bankroll percentage calculator

Works out the stake for a fixed percentage of your bankroll and the fraction the Kelly criterion suggests for your estimated probability.

Your bankroll% of bankroll per betDecimal oddsYour estimated probability (%)Kelly fractionFull KellyHalf KellyQuarter Kelly

Stake at the fixed percentage—

Full Kelly (% of bankroll)—

Stake at the chosen fraction—

Kelly depends entirely on your probability estimate; if it is optimistic the stake comes out too high, which is why a fraction is common. This is not a recommendation to bet.

How it works

Enter your bankroll and the percentage you set aside per bet: the stake comes out directly. For Kelly add the decimal odds and your estimated probability; the criterion shows the share of the bankroll that maximises long-run growth if your estimate were exact.^[1] Because an estimate is rarely exact, a fraction (half or quarter Kelly) is common: it lowers the stake and the swings.

Formulas

• Stake at a fixed percentage = bankroll × percentage / 100.
• Full Kelly: f = (p × D − 1) / (D − 1), where p is your probability and D the decimal odds.
• If f ≤ 0 there is no edge by your estimate and Kelly is 0. Stake at a fraction = bankroll × f × fraction.

Worked example

With a bankroll of 1000: 2% is 20.00. At odds 2.10 and an estimated probability of 50%, full Kelly is 4.55% of the bankroll; quarter Kelly is 1.14%, which is 11.36.

Things to keep in mind

• Kelly depends entirely on your probability estimate: if it is optimistic, the stake comes out too high.
• Full Kelly produces large swings in the bankroll, which is why most people use a fraction.
• This calculator does not recommend betting: it only does arithmetic with the numbers you enter.

Next steps

• Kelly needs an edge and the edge needs a probability: calculate the expected value first.
• For a market reference without the margin, remove the bookmaker's margin from the odds.
• If you would rather start from the amount you want to win than from the bankroll, start from the profit you want.

Frequently asked questions

What is the Kelly criterion?

A formula for the share of the bankroll to stake to maximise long-run growth, given the odds and your estimated probability.

What percentage of my bankroll should I bet?

There is no universal number. Many use a low fixed percentage; Kelly is only useful if your probability estimate is reliable.

What is quarter Kelly?

25% of the stake full Kelly indicates, to limit the damage of a wrong estimate.

What if Kelly is 0?

By your estimate the odds offer no edge and the criterion does not suggest a bet.

To convert odds formats use the odds calculator.

18+. Take part only where it is legal. Betting carries a risk of loss. Do not treat potential returns as a budget and do not chase losses. If gambling stops being under control, stop and look for help from the support services in your country.

Notes and sources

1. Wikipedia. Kelly criterion. Checked on 05/11/2026.