Definition
Overround is the amount by which the implied probabilities of all outcomes in a bookmaker's market add up to more than 100%. If a two-way market is priced so the implied chances total 105%, the overround is 5% and that is, broadly, the bookmaker's built-in margin on the market - the theoretical hold if the book takes balanced action across the outcomes.
It is also called the book percentage, the vig or the juice.
Overround varies by sport, by market (main lines are keener than props or long accumulators), by operator and by event profile. A lower overround on a market genuinely means better value there, and comparing it across operators is one of the few objective measures of how competitive a book's pricing is.
In context
For affiliates, overround is one of the most genuinely useful, objective things a sportsbook review can quantify, and it is under-covered because it takes work. Content that calculates and shows the overround on comparable markets - the main match-result market of a top league, say - across several operators gives readers a real basis for choosing where to bet, in contrast to reviews that rank on bonus size.
It also supports the practical advice to line-shop, since the differences in price between books are money.
The honest framing is that a lower overround is better value but does not make betting profitable - the margin still favours the book, and it compounds across the legs of an accumulator, which is why long accas have a far worse effective overround than singles. Content should show overrounds by market type so readers understand props, specials and multi-leg bets carry higher margins than main markets, present overround as a value-comparison tool rather than a route to winning, and carry age-gating and responsible-gambling messaging.
Ranking operators partly on the overround of their core markets is a defensible, reader-serving methodology. For affiliate-facing content, the framing is that overround is how far a market's implied probabilities exceed 100% and approximates the bookmaker's margin, that it varies by market and operator, that a lower overround is better value but not a profit route, and that comparing it across operators on comparable markets is a strong, objective review measure.
Worked example
An affiliate's sportsbook comparison calculates the overround on the same top-league match-result market across five operators (from about 103% to 108%) and on a player-props market (all above 110%), showing which book offers better value on core markets. It explains lower overround is better value but the book still holds an edge, and carries responsible-gambling messaging.
Related terms
Frequently asked questions
Browse more iGaming terms in our glossary.
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