Kelly calculator: the stake your edge deserves
Odds, win probability, bankroll — the Kelly criterion turns them into the stake that maximizes long-run growth, and tells you plainly when the right stake is zero.
Set the numbers to size the bet.
How it works
f = (bp − q) ÷ b, with b the decimal odds minus 1, p your win probability, q = 1 − p. It's the fraction of bankroll that maximizes expected log growth. It is also brutally sensitive to p: overestimate your edge and full Kelly over-bets it — which is why the half and quarter stakes are on the card. When f comes out negative, the formula is telling you the price is worse than your probability: no bet.
Frequently asked questions
What is the Kelly criterion?
The stake size that maximizes long-run bankroll growth: f = (bp − q) / b, where b is the decimal odds minus 1, p your win probability, q = 1 − p. Positive edge → positive fraction; no edge → bet nothing.
Why do sharps bet half or quarter Kelly?
Full Kelly assumes your probability estimate is exact. It never is — and over-betting an overestimate costs far more than under-betting. Fractional Kelly gives up a little growth for a lot of survival.
Standard formulas on numbers you provide — not betting advice. 21+ where applicable. Gambling problem? Call 1‑800‑GAMBLER.