Margin Calculator

Calculate bookmaker margin and overround

Bookmaker margin can be estimated by converting every outcome price into an implied probability and adding the percentages together. A perfectly fair market totals 100%. A total above 100% is commonly called the overround.

Enter two to four mutually exclusive outcome prices. The calculator reports the total implied probability, overround and normalized no-vig probability and fair decimal price for each entered outcome.

Example

If a two-way market implies 52% for one side and 53% for the other, the total is 105% and the overround is 5 percentage points. Normalizing both probabilities back to 100% provides a simple estimate of the market’s fair probability split.

What margin does not tell you

Overround shows the structure of the quoted prices, not whether either side is a good bet. Bookmakers can distribute margin unevenly, and market liquidity, limits and promotional pricing can affect individual prices.