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Kelly Criterion Calculator

The Kelly criterion converts an edge into a stake size: bet the fraction of your bankroll that maximises long-run growth, and nothing when there is no edge. It is the answer to the second question of betting: not what to bet, but how much.

Enter your bankroll, the decimal odds, and your win-probability estimate. The calculator returns the edge, the full-Kelly percentage, and the recommended stake at your chosen fraction. Most disciplined bettors size at a quarter Kelly. It keeps ~88% of the growth at a fraction of the drawdowns.

Kelly fraction

Edge

10.00%

Full-Kelly %

10.00%

Recommended stake

€25.00

How to use the Kelly Calculator

  1. 1

    Enter your current bankroll in EUR: the total amount you have set aside for betting.

  2. 2

    Enter the decimal odds on offer and your estimated win probability in percent (a de-vigged fair probability is the usual source).

  3. 3

    Pick a Kelly fraction (quarter Kelly is the standard for most bettors) and read the recommended stake. 'No bet' means the edge is non-positive.

Worked examples

Example 1: the classic 55% at 2.00

Bankroll €1,000, odds 2.00, win probability 55%. Edge = 2.00 × 0.55 − 1 = +10%. Full Kelly = (1 × 0.55 − 0.45) / 1 = 10% of bankroll → €100. At quarter Kelly the recommended stake is €25.

Example 2: no edge, no bet

Odds 1.80 at a 50% win probability: edge = 1.80 × 0.50 − 1 = −10%. Kelly returns a stake of €0. There is no stake size that turns a negative-EV bet positive. This is Kelly's most underrated feature: it tells you when not to bet.

FAQ

Kelly Criterion FAQ

What is the Kelly criterion?
The Kelly criterion is a staking formula that maximises the long-run growth rate of a bankroll: f* = (b·p − q) / b, where b is the decimal odds minus 1, p is your win probability, and q = 1 − p. It answers 'how much should I bet?' given an edge. Bet too little and you leave growth on the table, bet too much and drawdowns destroy the bankroll even with a real edge.
Why do most bettors use fractional Kelly (half or quarter)?
Full Kelly assumes your probability estimate is exactly right. In practice it never is, and overestimating your edge with full-Kelly stakes is ruinous, because betting more than 2× the true Kelly fraction has a negative expected growth rate. Quarter Kelly captures roughly 88% of full Kelly's growth rate while cutting expected drawdowns by about 75%. That trade is why most disciplined bettors size at a quarter to a half Kelly.
What does it mean when the calculator says 'No bet'?
If your estimated win probability times the decimal odds is below 1, the bet has negative expected value. There is no stake size that makes a losing proposition profitable. Kelly's answer to a negative edge is always zero.
Where do I get the win probability from?
That is the hard part. Kelly only sizes a bet, it doesn't find one. A common reference is the no-vig fair probability derived from a sharp book's odds (de-vig Pinnacle's line and use the fair percentage). Our no-vig calculator does exactly that conversion. Whatever source you use, be conservative: Kelly punishes overconfidence far more than caution.
Does Kelly guarantee I won't go broke?
Kelly staking with accurate probabilities never bets the full bankroll, so formally it cannot hit zero, but real bettors misestimate probabilities, and books limit accounts. Expect deep drawdowns even when sized correctly: full Kelly has a 1-in-3 chance of halving your bankroll at some point. Variance is the price of growth; fractional Kelly reduces the price.

BetEdge is an analytics and decision-support tool, not a bookmaker and not a tipster service. We don't accept bets or hold funds. For educational and informational purposes only. 18+.

No-vig fair odds calculator →EV calculator →The math behind value betting →