Kelly Criterion Calculator
Calculate the optimal fraction of your bankroll to stake on a bet using the Kelly Criterion to maximise long-run capital growth.
Results
What is it?
The Kelly Criterion (John L. Kelly Jr., 1956) is a mathematical formula that calculates the optimal fraction of your bankroll to wager in order to maximise the expected logarithm of wealth รขโฌโ i.e., long-run capital growth. It perfectly balances growth against the risk of ruin.
How to use
Enter your estimated win probability for the bet, the decimal odds on offer, your total bankroll, and the Kelly fraction you want to apply. Full Kelly (100%) maximises theoretical growth but causes extreme volatility. Quarter Kelly (25%) is far more practical for real-world use and reduces variance dramatically.
Example scenario
You estimate a 55% chance of winning a bet at 2.00 decimal odds (even money). Full Kelly = ((1 รโ 0.55 รขหโ 0.45) / 1) = 10% of bankroll. On a $1,000 bankroll, Full Kelly stake = $100. Quarter Kelly = $25 รขโฌโ much safer but still captures positive expected value since Edge = (0.55 รโ 2.00 รขหโ 1) รโ 100 = +10%.
Pro tip
Only use Kelly when Edge > 0%. A negative Kelly result means the bet has negative expected value รขโฌโ do not bet. Never use Full Kelly in practice; it produces catastrophic drawdowns. Half or Quarter Kelly is the professional standard. Accurate probability estimation is the hardest part: overestimating your edge leads to overbetting and accelerated ruin.