Overround is one of the fundamentals of bookmaking, and is applied to every event by all UK betting sites.
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Overround → apply → sites
It is how bookies factor in a profit to every market they run and is a vitally important concept to help understand how bookies work.
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bookies → factor → market
In this guide, The Standard have looked at how the overround works and how bettors can work out what the overround is on a particular market.
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overround → look → market
Overround is the sports betting term for the built-in margin a bookmaker adds to a betting market.
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bookmaker → build → market
It is the amount by which the implied probabilities of all possible outcomes add up to more than 100 per cent.
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probabilities → imply → cent
This margin gives bookmakers an edge regardless of which selection wins.
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selection → give → edge
Rather than needing to correctly predict every result, the bookmaker prices the market so the total implied probability exceeds 100 per cent, creating room for a profit over time.
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probability → need → time
How overround works
To calculate implied probability from decimal odds, divide 100 by the odds.
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overround → work → odds
The formula is: implied probability (%) = 100 divided by decimal odds.
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formula → imply → odds
The first selection has an implied probability of 40%, while the second is 31.25%.
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second → have → %
Adding those figures gives a total implied probability of 116.25%.
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Adding → add → %
The overround is therefore 16.25%, representing the bookmaker's built-in margin in that market.
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overround → represent → market
A market priced at exactly 100% would have no overround, although bookmakers generally build a margin into their prices.
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bookmakers → price → prices
Why overround matters for bettors
A lower overround generally means the bookmaker has taken a smaller margin, which can result in better value odds for bettors.
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which → matter → bettors
A higher overround means a larger margin has been built into the prices, leaving less value in the market if all other factors are equal.
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factors → mean → market
Overround also varies between markets.
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Overround → vary → markets
It tends to be tighter where there is more liquidity, such as major sporting events, markets close to the start time and highly traded competitions.
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It → tend → time
Smaller or more niche markets can carry wider margins because there may be less betting activity and fewer competing prices.
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markets → carry → margins
Comparing the overround for the same market across different betting sites can therefore provide a quick sense check on how competitively the betting odds are priced.
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odds → compare → check
Bettors can make the same comparison when using betting apps, although the margin remains only one factor to consider.
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margin → make → apps
Overround in horse racing and other sports
Overround applies across sports betting, but is particularly prevalent on greyhound and horse racing betting sites.
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Overround → apply → sites
It is particularly visible in horse racing markets with large fields, where bookmakers must price more possible winners.
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bookmakers → price → winners
Bettors looking at horse racing markets can use the same calculation to understand the margin built into a market, while the principle also applies to football, tennis, boxing and other sports.
Overround in betting - FAQs
What does overround in betting mean?
Overround is the amount by which the implied probabilities of all outcomes in a betting market exceed 100%.
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probabilities → look → %
It represents the bookmaker's built-in margin and is calculated by adding the implied probabilities of every possible outcome.
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It → represent → outcome
Does overround affect all types of bets?
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overround → affect → bets
Overround is baked into most betting markets.
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Overround → bake → markets
The size of a bookmaker’s margin varies depending on the sport, market and liquidity, so it can differ between straightforward match bets and more specialised markets.
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it → vary → bets
The Aporia
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