Kelly Staking Calculator
Finding value is half the job. Kelly tells you how much of your bankroll each value bet deserves, so the pot grows without one bad weekend wrecking it.
Kelly Stake Sizer
Enter odds, win chance and bankroll to get your stake
Accepts decimal (2.50), American (+150, -200), or fractional (5/2) odds
The formula in plain English
Kelly stakes a share of your bankroll in line with your edge. Bigger edge, bigger stake. No edge, no bet.
Kelly % = (b × p − q) ÷ b
Here b is the decimal odds minus 1, p is your win chance and q is 1 − p.
A value bet on a £500 bank
You make the away side a 52% shot and they're 2.10. b = 1.10, so Kelly = (1.10 × 0.52 − 0.48) ÷ 1.10 = 8.36%. Full Kelly says £41.82. Half Kelly says £20.91, and that's where I'd leave the dial.
Why half beats full
Kelly assumes your probability is exactly right. It never is. Nudge that 52% up to 54% and full Kelly jumps to 12.18%: nearly half as much again, on a two-point guess. Halving the stake protects you from your own optimism and smooths the swings while the bank still grows.
Half Kelly on a £500 bank
| Odds | Your chance | Full Kelly | Half Kelly stake |
|---|---|---|---|
| 2.10 | 52% | 8.36% | £20.91 |
| 3.40 | 33% | 5.08% | £12.71 |
| 1.62 | 64% | 5.94% | £14.84 |
| 5.50 | 20% | 2.22% | £5.56 |
| 2.40 | 40% | — | No bet |
Staying disciplined
- •Work from today's bank. Recalculate after every result, not from the figure you started the season with.
- •Untested numbers, quarter Kelly. If your probabilities come from a model you haven't proved yet, the quarter setting is the honest one.
- •Negative means no. When the formula comes out below zero there's no edge. Respect it and keep your money.
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