Tool · Calculator
Kelly criterion calculator
The Kelly criterion tells you what fraction of your bankroll to stake to maximise long-run growth given your edge. Enter your win probability, the decimal odds, and your bankroll — and use half- or quarter-Kelly to keep the swings survivable.
Kelly stake
10.0%
Recommended $
$100.00
Edge (EV / $1)
+10.0%
Full Kelly maximises long-run growth but swings hard. Most pros bet half or quarter Kelly to cut variance — your probability estimate is never exact.
How it works
- Formula: f* = (b·p − q) / b, where b = decimal odds − 1, p = your win probability, q = 1 − p.
- No edge, no bet: if your probability doesn't beat the odds' implied chance, Kelly returns zero — don't bet.
- Fractional Kelly: your probability estimate is never exact, so full Kelly over-bets in practice. Half or quarter Kelly keeps most of the growth with far less variance.
- Need a probability? Prediction markets give a live, money-weighted estimate — sanity-check yours on the Odds Desk.