Enter your bankroll, win probability, and the offered odds to size the bet.
Pure math only. Not financial advice; no real-money handling.
About this tool
The Kelly Criterion Stake Calculator works out the bet size that maximizes the long-run growth of your bankroll for a given edge. With net fractional odds b = decimal odds − 1, your win probability p, and loss probability q = 1 − p, the full-Kelly fraction of bankroll to stake is f* = (b·p − q)/b, which is equivalent to (p·decimal − 1)/(decimal − 1) — that is, your edge divided by b. If f* is zero or negative you have no edge, and the tool advises no bet.
Because full Kelly is famously volatile, the calculator also supports fractional Kelly: choose half (×0.5) or quarter (×0.25) and it scales the recommended fraction and stake accordingly, trading some growth for a much smoother bankroll. It multiplies the chosen fraction by your bankroll to give a concrete recommended stake, and also reports your edge, edge% = p·decimal − 1. For example, at even-money decimal 2.00 with a 55% edge estimate, f* = (1×0.55 − 0.45)/1 = 0.10, so full Kelly stakes 10% of the bankroll.
All computation happens locally in your browser with nothing uploaded. This is a pure mathematics tool — not financial or betting advice, with no real-money handling. Kelly assumes your probability estimate is accurate; since real estimates are uncertain, many bettors deliberately use half or quarter Kelly.
Frequently asked questions
What is the Kelly Criterion formula?
f* = (b·p − q)/b, where b = decimal odds − 1, p is your win probability, and q = 1 − p. Equivalently f* = (p·decimal − 1)/(decimal − 1), your edge divided by b. It gives the bankroll fraction that maximizes long-term growth.
What is fractional (half/quarter) Kelly?
Fractional Kelly multiplies the full-Kelly fraction by a constant like 0.5 or 0.25. It stakes less, sacrificing some growth for much lower volatility and drawdowns — a common safeguard because real win-probability estimates are never perfect.
What does a zero or negative Kelly mean?
It means p·decimal ≤ 1, so the bet has no positive expected value at your estimated probability. Kelly then recommends staking nothing — betting into a negative edge shrinks your bankroll over time, so the tool advises no bet.
What win probability should I enter?
Your own honest estimate of the true chance the bet wins, as a percentage (0–100) or a decimal between 0 and 1. Kelly is only as good as this estimate; overstating it leads to over-betting, which is why fractional Kelly is popular.