Kelly Criterion Calculator for Sports Betting
The Kelly criterion tells you how much of your bankroll to bet based on your edge. Used carelessly, it can also bet you broke. This calculator shows full Kelly for reference but defaults to a safer fraction, with a hard cap on any single bet.
The formula, simply
- Kelly % = (b × p − q) ÷ b, where p is your win probability, q = 1 − p, and b is the profit per $1 risked (0.909 at −110).
- Example: a 56% chance at −110 gives a full-Kelly bet of about 7.6% of bankroll.
Why we default to quarter Kelly
- Full Kelly assumes your win probability is exactly right. It never is. Betting a quarter of the Kelly amount gives up a little growth in exchange for far smaller swings and much lower risk of ruin.
- We also cap any single bet at 3% of bankroll, no matter what the formula says.
No edge, no bet
If the formula returns zero or a negative number, the right bet size is nothing.
FAQ
What is a good Kelly fraction?
Many professional bettors use between one-quarter and one-half Kelly. We default to one-quarter.
Can I use Kelly with parlays?
You can, but parlay probabilities are harder to estimate accurately, which makes oversizing more likely. Be extra conservative.
Does Kelly guarantee profit?
No. It only sizes bets well if your probabilities are accurate. It does not create an edge.