Kelly Criterion Calculator
Kelly sizes your bet to your edge. Most bettors use Half or Quarter Kelly — it gives up a little growth for far smaller swings, and it protects you when your win-probability estimate is a little off (it usually is).
How Kelly sizing works
The Kelly Criterion answers the question every bettor should ask before risking a dollar: how much? It sizes your bet to your edge — bigger when the gap between your probability and the price is large, smaller when it's thin, and zero when there's no edge at all.
The catch is that Kelly assumes your win probability is exactly right. It almost never is, which is why seasoned bettors scale down to Half or Quarter Kelly. You give up a little theoretical growth in exchange for much smaller drawdowns and protection against your own estimation error.
Kelly only works if your probabilities are honest. That is the hard part — and it is exactly what our model does: it calculates a true line for every game so the edge you size against is grounded in data, not a hunch.
Frequently asked questions
What is the Kelly Criterion?
The Kelly Criterion is a formula that sets your stake as a fraction of bankroll based on your edge: f = (b·p − q) / b, where b is the decimal odds minus one, p is your win probability, and q is 1 − p. It maximizes long-run bankroll growth while never risking ruin.
Should I use full Kelly?
Most disciplined bettors use Half or Quarter Kelly. Full Kelly produces the fastest theoretical growth but brutal swings, and it assumes your win probability is exactly right. Since your estimate is always a little off, fractional Kelly gives up a sliver of growth for far more stability.
What if Kelly says to bet nothing?
A zero or negative Kelly stake means your win probability is below the break-even rate the odds imply — there is no edge, so the correct bet size is zero. Kelly only tells you to bet when you are getting a better price than your probability deserves.