# Kelly criterion calculator

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Canonical: https://novigapi.com/kelly-criterion-calculator
Method checked: 2026-11-12
Interactive tool: https://novigapi.com/kelly-criterion-calculator (prefill with ?a=&b=)

The Kelly stake is f = (b x p - q) / b, where b is decimal odds minus 1, p your win probability and q = 1 - p. At 55% and -105, full Kelly is 7.75% of bankroll. Most bettors use half or quarter Kelly. A no-vig exchange mid, such as Novig's, is a common source for p (Novig docs, checked 12 Nov 2026).

## Worked example

Worked example: 55% at -105, $1,000 bankroll

| Fraction | Share | Stake |
| --- | --- | --- |
| Full Kelly | 7.75% | $77.50 |
| Half Kelly | 3.88% | $38.75 |
| Quarter Kelly | 1.94% | $19.38 |

```
f* = (b x p - q) / b
b = decimal odds - 1, q = 1 - p
```

Kelly maximises the long-run growth rate of a bankroll when p is known exactly. It never is, and overbetting is far worse than underbetting: at twice full Kelly the expected growth rate falls to zero. That is why fractional Kelly is the norm. A negative result means the bet has negative EV at that price: do not bet.

## How to use it

1. Enter your win probability.
2. Enter the price offered and your bankroll.
3. Read the full, half and quarter Kelly stakes.

## Questions

### Is full Kelly too aggressive?

Usually. Errors in p are common, and full Kelly punishes them. Half or quarter Kelly keeps most of the growth with far less risk.

### What does a negative Kelly mean?

The bet has negative expected value at that price, so the optimal stake is zero.

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