The vig (short for "vigorish") is the sportsbook’s built-in margin on a wager — the difference between true probability and the offered odds. On standard -110/-110 markets, the vig is about 4.5%, meaning the book expects to keep $4.50 of every $100 wagered, on average.
Also known as: juice, overround, margin
A truly 50/50 outcome would pay even money (+100). At -110/-110 you risk $110 to win $100 on either side, and that gap is the vig. Reduced-juice books offer -105/-105 (≈2.4% vig); pick-em books occasionally run -102/-102.
Vig is the sportsbook equivalent of house edge — a long-run margin, not a per-bet guarantee. Sharp bettors track closing-line value to confirm they consistently beat the vig.
Parlay vig compounds across legs. A 4-leg parlay of -110 lines carries an implied vig closer to 18% than 4.5%. Same-game parlays and player props carry the highest margins on most sportsbooks.