Kelly Criterion Calculator
Find the mathematically optimal bet size for your edge.
How it works
Kelly maximizes long-term bankroll growth. Most pros bet a fraction (half-Kelly) to cut volatility. Bet more than full Kelly and your risk of ruin climbs fast.
In practice people use half or quarter Kelly — it markedly reduces variance and drawdown risk at the cost of slightly slower growth.
Kelly Criterion Calculator
The Kelly criterion is a formula for sizing bets so your bankroll grows as fast as mathematically possible without risking ruin. This free Kelly criterion calculator turns your decimal odds and estimated win probability into the exact optimal stake — plus the safer half-Kelly amount most professionals actually use.
How the Kelly criterion works
Kelly answers one question: what fraction of your bankroll should you bet when you have an edge? The formula is f = (bp − q) / b, where b is the net decimal odds (odds − 1), p is your win probability, and q = 1 − p.
If the result is zero or negative you have no edge, and Kelly correctly tells you not to bet. Only a genuine, repeatable edge makes the formula pay off.
Full Kelly vs half Kelly
Full Kelly maximizes long-term growth but produces wild swings — drawdowns of 50% or more are normal. Half Kelly keeps roughly three quarters of the growth while cutting volatility dramatically, which is why most serious bettors and investors bet a fraction of full Kelly.
Betting more than full Kelly is never optimal: growth falls and risk of ruin rises sharply.
How to use this calculator
Enter the decimal odds offered, your honest estimate of the win probability, and your current bankroll. The calculator shows your edge (expected value), the full and half Kelly fractions, and the exact stake in your currency.
What is the Kelly criterion?expand_more
A bet-sizing formula that picks the stake which maximizes the long-term growth rate of your bankroll, given your edge and the odds.
Should I use full or half Kelly?expand_more
Most people should use half Kelly. It keeps most of the growth while roughly halving the volatility and the risk of a deep drawdown.
What odds format does the calculator use?expand_more
Decimal odds. 2.00 means even money, 1.91 is the same as American −110, and 3.00 means a 2-to-1 payout.
Can the Kelly criterion guarantee a profit?expand_more
No. Kelly only helps when you genuinely have an edge. With no edge it tells you not to bet, and it cannot turn a losing game into a winning one.