Kelly Criterion Calculator
Use this free Kelly Criterion calculator to turn your edge and bankroll into a disciplined bet size. Enter the odds, your estimated win probability, and your bankroll, and the tool shows the exact Kelly stake, plus safer half and quarter Kelly amounts. It works with American or decimal odds.
What Is the Kelly Criterion?
The Kelly Criterion is a bet-sizing formula that tells you what fraction of your bankroll to stake when you believe you have an edge. Instead of betting a flat amount, you bet more when your edge is large and less when it is small, which maximizes long-run bankroll growth while protecting you from ruin. The calculator above does the math from your odds, win probability, and bankroll.
How to Use the Kelly Calculator
Pick your odds format, enter the price, then enter your honest estimate of how often the bet wins as a percentage. Add your current bankroll and choose a Kelly fraction. The tool returns the recommended stake in dollars and as a percentage of your bankroll, along with your edge and the full, half, and quarter Kelly amounts so you can pick a comfort level.
Worked Example
Say you back a bet at -110 (decimal 1.91) and you honestly believe it wins 55 percent of the time. Here b = 0.91, p = 0.55, and q = 0.45, so the full Kelly fraction is (0.91 times 0.55 minus 0.45) divided by 0.91, which works out to about 5.5 percent. On a $1,000 bankroll that is a $55 full Kelly stake, or a $27.50 half Kelly stake, which most bettors prefer. Your edge here is 5 percent expected value.
Why Most Bettors Use Half Kelly
Full Kelly assumes your win probability is exactly right. In real betting your estimate is never perfect, and full Kelly can produce painful swings. Betting half or quarter Kelly keeps most of the long-run growth while cutting the volatility dramatically, so it is the practical default for almost everyone. If your probability estimate is shaky, size down further.
Free Printable Kelly Worksheet
Want to work a stake out by hand before you bet? Download the free printable Kelly Criterion worksheet to record your odds, win probability, and bankroll, then compute the full, half, and quarter Kelly stakes step by step.
Download the Kelly Worksheet (PDF)
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Kelly Criterion Calculator FAQ
What is the Kelly Criterion in betting? The Kelly Criterion is a formula that sets your bet size as a fraction of your bankroll based on your edge. It maximizes long-run growth by betting more when your edge is bigger and less when it is smaller.
What is the Kelly formula? The Kelly fraction is f = (b times p minus q) divided by b, where b is decimal odds minus 1, p is your win probability, and q is 1 minus p. Multiply f by your bankroll to get the stake.
What is half Kelly? Half Kelly means staking 50 percent of the amount the full Kelly formula suggests. It keeps most of the long-run growth while sharply reducing bankroll swings, which is why most bettors use it.
What if the calculator says bet nothing? If the Kelly fraction is zero or negative, the odds do not beat your estimated win probability, so you have no edge. Kelly then tells you to bet nothing, because any stake loses money over time.
Is the Kelly Criterion safe? Full Kelly can be volatile because it assumes your probability is exact. Using half or quarter Kelly, and being honest about your win probability, makes it far safer while still growing your bankroll.
