The bookmaker's built-in profit margin — the amount by which the implied probabilities of all outcomes in a market sum to more than 100%.
The overround (also called the vig, juice, or margin) is the bookmaker's profit mechanism. If you add up the implied probabilities for all outcomes of a market — home win, draw, away win — they sum to more than 100%. The excess is the overround.
For example: home win at 2.10 (47.6%) + draw at 3.40 (29.4%) + away win at 3.80 (26.3%) = 103.3% total. The 3.3% overround means the bookmaker retains 3.3p for every £1 bet into this market on average.
A higher overround means worse value for bettors. Soft bookmakers often have overrounds of 7–12% on football markets. Sharp bookmakers like Pinnacle operate at 1–3%. This difference compounds significantly over thousands of bets.
To find the fair (no-margin) probability of each outcome, divide each implied probability by the total sum of all implied probabilities. This removes the overround and gives you the bookmaker's true assessment of each outcome.
Implied Probability
The probability of an outcome embedded in bookmaker odds — calculated by dividing 1 by the decimal odds.
Value Betting
Betting at odds that are higher than the true probability of the outcome — finding bets where the bookmaker has underestimated the chances of an event.
Expected Value (EV)
The average outcome of a bet over a large number of repetitions — positive EV means the bet profits long-term; negative EV means it loses.
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