Kelly Criterion Calculator

Enter the odds offered by the sportsbook in American, decimal, or fractional format. Then enter your win probability — how likely you believe the bet is to win — and your total bankroll.

Choose full, half, or quarter Kelly, or set a custom fraction. The calculator updates as you type and shows the recommended stake in dollars and as a percentage of your bankroll, your edge on the bet, the break-even probability implied by the odds, and the expected profit of the recommended wager.

The Kelly Criterion is a bankroll management formula developed by John L. Kelly Jr. at Bell Labs in 1956. It calculates the fraction of your bankroll to bet that maximizes the long-term growth of your bankroll, given the odds and your probability of winning.

In sports betting, Kelly sizing scales your stake to your edge. A small edge earns a small bet, a large edge earns a larger one, and a bet with no edge gets nothing. Because every stake is a percentage of your current bankroll, your bets shrink automatically during a losing run and grow as your bankroll grows.

Kelly % = (b × p − q) ÷ b

Where b is the net decimal odds (decimal odds minus 1), p is your probability of winning, and q is your probability of losing (1 − p).

Example: a bet at -110 (1.909 decimal, so b = 0.909) that you believe wins 55% of the time gives (0.909 × 0.55 − 0.45) ÷ 0.909 = 5.5%. With a $1,000 bankroll, full Kelly says bet $55; half Kelly says $27.50. The odds imply a break-even probability of 52.4%, so your 55% estimate gives you a 5% edge.

Full Kelly maximizes long-term growth, but only if your win probability is exactly right. It is also volatile: drawdowns of 50% or more are common even with a real edge.

Fractional Kellybets a fixed share of the full Kelly stake. Half Kelly keeps about three quarters of full Kelly's growth rate with roughly half the volatility, and quarter Kelly is more conservative still. Because overestimating your edge is the most common mistake in betting — and betting more than full Kelly actually shrinks your bankroll over time — most professional bettors use half or quarter Kelly.

The Kelly formula is only as good as the probability you put into it. A common approach is to remove the vig from a sharp sportsbook's line or the market consensus to get a fair probability, then look for a book offering better odds than that probability implies.

Our Positive EV Finder does this across 100+ sportsbooks and shows the de-vigged fair probability for each bet, which you can plug straight into this calculator. Need to convert a line first? Use the Odds Converter.

Kelly assumes you know your true edge, that each bet is independent, and that you can bet any amount. In reality your probabilities are estimates, sportsbooks cap stakes, and bets on the same game are correlated. Treat the result as a ceiling, not a target: if in doubt, use a smaller fraction.