Kelly criterion calculator
How much to stake on a +EV price: full, half and quarter Kelly from your bankroll, with an optional cap, net of exchange fees.
Inputs
Result
updates as you typeRun this math on every line, automatically
Every row of the +EV finder carries a Kelly stake from the multiplier you set on your Account page.
How it works
The Kelly criterion picks the stake that maximises the long-run growth rate of a bankroll when you know your edge:
f* = (b·p − q) ÷ b
b = d − 1 (net odds) · p = win probability · q = 1 − p · f* = fraction of bankroll
If f* comes out negative the price does not beat your probability and the stake is zero. Most bettors stake a fraction of Kelly (a half or a quarter) because the true probability is never known exactly, and full Kelly punishes an overestimated edge hard. A cap (for example 2% of bankroll) keeps one bet from ever being too large.
Worked example
You believe a +120 price wins 50% of the time and you have a $1,000 bankroll.
b = 2.2000 − 1 = 1.2000, p = 0.50, q = 0.50
f* = (1.2000 × 0.50 − 0.50) ÷ 1.2000 = 8.33%
EV = 0.50 × 2.2000 − 1 = +10.00%
| Kelly fraction | Share of bankroll | Stake |
|---|---|---|
| Full | 8.33% | $83.33 |
| Half | 4.17% | $41.67 |
| Quarter | 2.08% | $20.83 |
| Tenth | 0.83% | $8.33 |
Things to watch
- Kelly assumes your probability is right. Overstate the edge and full Kelly overbets. Fractional Kelly is the usual protection.
- Simultaneous bets. Kelly is for one bet at a time. Many open bets at once share the same bankroll, so scale down.
- Correlated bets (same game, same player) are not independent; treat them as one larger position.
- Fees change the edge. Pick the venue so the stake is sized on your net price.