Margin and fair odds calculator
Enter the odds on every outcome of one market. The implied probabilities add up to more than 100%: the excess is the overround, and the bookmaker keeps 4.55% of every stake on a -110 / -110 line.
Typical margins
| Market | Odds offered | Overround | Margin | Fair odds without the margin |
|---|---|---|---|---|
| US line, -110 on both sides | 1.91 / 1.91 | 4.76% | 4.55% | 2.00 / 2.00 |
| Football match result 2.50 / 3.30 / 2.90 | 2.50 / 3.30 / 2.90 | 4.79% | 4.57% | 2.62 / 3.46 / 3.04 |
| Tennis match 1.50 / 2.50 | 1.50 / 2.50 | 6.67% | 6.25% | 1.60 / 2.67 |
How it works
- Overround = sum of 1 / odds over all outcomes, minus 1.
- Margin = 1 - 1 / (sum of 1 / odds). It is the share of stakes the bookmaker keeps on average if the true chances match its prices, and it is the same on every outcome.
- Fair probability of an outcome = (1 / its odds) / sum; fair odds = 1 / fair probability. This spreads the margin in proportion to the prices, the simplest and most common method.
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