Overround

Overround is the technical expression of how bookmaker margin is constructed. On a fairly-priced two-way market, the implied probabilities of each outcome would sum to exactly 100%. By pricing each outcome slightly tighter than true probability, the bookmaker creates an overround: the implied probabilities sum to more than 100%, with the excess being the structural margin. A 4% overround on a two-way market produces approximately a 4% expected return for the bookmaker across enough matched volume. Overround levels vary substantially by market and event. The biggest sports and most competitive events have the tightest overrounds (because pricing efficiency matters most, and competitive pressure tightens margins). Lower-profile and lower-liquidity markets run wider, sometimes substantially. In-play overrounds are typically wider than pre-match because the trading complexity is higher. Operator-level overround disclosure isn't common in earnings releases; the metric is observable to traders and bettors analyzing specific markets.