Bookmaker margin explained: why prices add to more than 100%
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Convert every outcome in a complete market into implied probability, then add the percentages. The amount above 100% is the quoted overround, often called the bookmaker margin.
A two-outcome market at 1.90 / 1.90
Each side: 1 ÷ 1.90 × 100 = 52.63%. Together: 105.26%. Subtract 100% to get an overround of about 5.26%.
| Market prices | Probability total | Overround |
|---|---|---|
| 2.00 / 2.00 | 100% | 0% |
| 1.95 / 1.95 | 102.56% | 2.56% |
| 1.90 / 1.90 | 105.26% | 5.26% |
What it measures
Overround describes how the quoted prices fit together. It is useful when comparing complete versions of the same market. It does not reveal the operator’s actual stakes, liabilities, costs or eventual profit.
Why another site may show 5.00%
Another common calculation divides the overround by the probability total. Here, 5.26 ÷ 105.26 × 100 is approximately 5.00%. That is a different measure from the 5.26% overround. Check which calculation a site uses before comparing its figures.
Three common mistakes
- Leaving out the draw in a three-outcome market.
- Combining different times or different lines.
- Treating a lower average as proof of the best price on every selection.
A lower overround is a useful price characteristic. It does not make a bet safe or prove an outcome is mispriced.
Sources
Sources checked 2026-09-05. Examples are illustrative unless labelled otherwise.
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