Skip to content

Bookmaker margin (overround)

A bookmaker’s margin, or overround, is how far a market’s implied probabilities add up past 100%. It is the built-in edge the bookmaker holds over the bettor.

Example

1.91 on both sides of a two-way market implies 52.4% each: 104.7% in total, a margin of 4.7%.

Go further

What the bookmaker's margin really costs youThe full explainer, on the blogImplied probability calculatorThe chance each price implies, the bookmaker’s margin and the fair odds without it.

Related terms

Implied probabilityImplied probability is the chance a price represents: 1 divided by the decimal odds. It includes the margin, so a market’s prices add up to more than 100%.Favourite-longshot biasThe favourite-longshot bias is the finding that bets on long shots lose more per unit staked than bets on favourites: they win less often than their odds imply.Line shoppingLine shopping is comparing the price for the same bet across bookmakers and taking the best. Over many bets, a slightly better price makes a real difference.