Kelly Calculator

What the Kelly criterion does

The Kelly criterion sizes a bet to maximize long-run bankroll growth. Given a real edge, it stakes a fraction of your bankroll equal to f = (b×p - q) / b, where b is decimal odds minus one, p is your win probability, and q is 1 - p. No edge means Kelly stakes nothing: the formula refuses -EV bets by design.

Full Kelly is aggressive and assumes your probability is exactly right. Since your estimate is never perfect, most disciplined bettors use half Kelly or quarter Kelly, which give up a little growth for a large drop in variance and risk of ruin. This calculator defaults to half Kelly for that reason.

How to use it

The hard input is an honest win probability. Get it by de-vigging a sharp line with the No-Vig Calculator, then confirm the bet clears the bar with the EV Calculator. For live plays where the edge is already computed, see the +EV Plays board and stake each one by Kelly.

Keep going

The Odds Gap holds every book's price, so you do not have to type them in by hand. Skip straight to the live tools: