Every sports bet you place carries a hidden fee called the vig — short for vigorish, also known as the juice or bookmaker margin. It is the commission baked into the odds, and it is the reason bookmakers profit no matter who wins the game.

Here is how it works: if a fair coin flip paid out at true 2.00 odds on both sides, the bookmaker would break even. Instead, you will typically see 1.91 on each side. That gap is the vig — roughly 4.5% the book keeps on balanced action.

To calculate vig, convert both sides' odds to implied probabilities and add them. Anything over 100% is the bookmaker's margin. For example, two outcomes at 1.91 decimal odds imply 52.36% each, totaling 104.72% — a 4.72% vig.

Smart bettors always compare the vig across sportsbooks before placing a bet. A book offering 1.95/-110 versus one offering 1.91 is giving you measurably better value on every single wager, and that compounds fast over a season.