Calculate the mathematically optimal stake size for your bets using the Kelly Criterion. Input your edge, odds and bankroll to maximize long-term growth while minimizing risk of ruin.
Kelly Calculator
What is the Kelly Criterion in Betting?
The Kelly Criterion is a mathematical formula developed by John L. Kelly Jr. in 1956. It determines the optimal percentage of your bankroll to wager on a bet to maximize long-term growth while controlling risk.
The basic formula is:
f = (bp – q) / b
Where:
- f = fraction of bankroll to bet
- b = decimal odds minus 1 (net odds)
- p = your estimated probability of winning (as decimal)
- q = probability of losing (1 – p)
Our free Kelly Criterion calculator does the math instantly and shows both full Kelly (aggressive) and half Kelly (safer, reduces variance).
How to Use the Kelly Criterion Calculator
It’s quick and straightforward:
- Enter your current Bankroll (total money available for betting).
- Input the Decimal Odds of the bet (e.g., 2.20 for +120 in American odds).
- Enter your estimated Win Probability (as percentage or decimal – must be higher than the implied probability from the odds to have edge).
- Click Calculate Kelly Stake.
- See recommended bet size (% of bankroll) for full Kelly and half Kelly, plus expected value and risk stats.
Example: Bankroll $1,000, odds 2.50 (implied prob 40%), your edge gives 48% win prob → full Kelly suggests ~6.4% stake ($64), half Kelly ~3.2% ($32) for lower risk.
Why Use the Kelly Criterion Calculator?
- Maximizes long-term bankroll growth when you have a real edge.
- Prevents over-betting and reduces risk of ruin compared to flat staking.
- Free, instant, no sign-up – perfect for serious bettors who track their edge.
- Shows half Kelly as a conservative option (popular among pros to cut variance).
Important tip: Kelly works best when your probability estimate is accurate. Overestimate your edge and you risk big drawdowns. Many users start with fractional Kelly (¼ or ½) to stay safe.