The sportsbook margin (also "vig" or "overround") is the theoretical edge a bookmaker builds into odds, calculated as the sum of implied probabilities minus 100%.
Sportsbook Margin / Vig
TL;DR: The sportsbook margin (also "vig" or "overround") is the theoretical edge a bookmaker builds into odds, calculated as the sum of implied probabilities minus 100%.
What it means
Bookmakers price markets so the implied probabilities of all outcomes add up to more than 100%. That surplus is the margin. On a fair-priced coinflip, both sides should be 2.00 (50/50). A bookmaker prices both at 1.91 — implied probs 52.4% each, sum 104.8%, margin = 4.8%.
Margin varies massively by market: football 1X2 (Tier 1 leagues) 3–6%; football 1X2 (Tier 5 leagues) 8–12%; tennis 4–7%; props and player markets 8–15%; SGP/parlays 15–25%+ effective.
Formula / How it's measured
Overround = (Σ 1 / decimal_odds × 100) − 100 Margin % = Overround / (100 + Overround) × 100
Example: 1X2 priced at 2.10 / 3.40 / 3.60. Implied probs = 47.6% + 29.4% + 27.8% = 104.8%. Overround = 4.8%, margin = 4.58%.
Why it matters for operators
Margin is the sportsbook's pricing lever. Tighter margins (lower vig) attract sharp players and competitive comparison; wider margins protect against losses but reduce competitiveness on price-comparison sites (Oddschecker, Pinnacle benchmarks). Modern sportsbook product strategy is to push players from low-margin singles toward high-margin parlays/SGPs — this is the entire US sportsbook playbook 2022–2026.
Common benchmarks (2026)
- Top football leagues 1X2: 3–6% margin
- Lower-tier sports: 6–10%
- Player props: 8–15%
- Same-game parlays: 15–25%
- Live in-play markets: 7–12%
- Blended bookmaker actual hold: 7–10% (margin × bet mix + variance)
Common mistakes
- Identical margin across markets and competition levels (sharp players exploit Tier 5 mispricing)
- Loose live-betting margins relative to staffing capacity (model latency = losses)
- Showing reduced margin on bonus bets without expected-value adjustment
See also