What Is the Vig in Sports Betting?
The vig (also called juice or the overround) is the built-in house edge in every sportsbook price. Here is how it works, why a -110/-110 line skims about 4.5%, and the win rate you need just to break even.
The vig (also called the juice, the margin, or the overround) is the house edge built into every sportsbook price. It is how books profit whether or not they predict games well, and it is the hurdle every winning bettor has to clear.
How it hides in the price
A typical coin-flip market is posted at -110 on both sides. At -110 you risk $110 to win $100, so each side implies a 52.38% chance (110 / 210). Add the two sides together and you get 104.76%, even though real probabilities can only sum to 100%.
That extra 4.76% is the overround, the book’s margin. On a true 50/50 game, fair odds are +100 on each side. The book shades both to -110, and the gap between the two is its guaranteed cut.
Why -110 already favors the book
Because of the vig, winning exactly half of your -110 bets loses money. To break even you have to win 52.38% of them. Every percentage point below that is profit for the book, and over hundreds of bets that small edge is what funds the building.
Beating it
The only way to win long-term is to find prices where the book’s number is wrong by more than its margin. That means having your own estimate of the true probability, converting it to fair odds, and betting only when the offered price clears both the gap to fair and the vig on top.
Fairline strips the vig out when it computes fair odds, then flags a play only when the best available book price beats fair by at least 3%, enough to clear a standard margin with room to spare.