Overround

The bookmaker's built-in margin on a market. Calculated as the amount by which the implied probabilities of all outcomes exceed 100%. A market priced at 1.91/1.91 implies 52.4% + 52.4% = 104.8% — the extra 4.8% is the overround. Equivalent terms: vig, vigorish, juice (US-leaning), margin. UK football match betting typically runs 4-7%; lower-league or niche markets 7-10%.

On accumulators, overround compounds across legs. A 5% per-leg margin becomes 18.5% on a four-fold and 33.7% on an eight-fold. This is the structural reason why long multiples favour the bookmaker disproportionately to short bets — and why margin awareness is foundational to value betting.