Open almost any two-sided market — a spread, a total, a moneyline between two closely matched teams — and you’ll usually see both sides priced around −110. Convert each side to an implied probability (see how American odds work) and you get roughly 52.4% and 52.4%. Add them up: 104.8%, not 100%.

That extra 4.8% is the vig (short for “vigorish,” also called juice or hold) — the sportsbook’s built-in margin. It’s not a separate fee you see on a receipt; it’s baked directly into both prices.

Why it exists

A sportsbook isn’t trying to predict the outcome for its own sake — it’s trying to balance action on both sides and collect a consistent margin regardless of who wins. The vig is that margin. It’s the same basic idea as a currency exchange counter quoting a slightly worse rate in both directions, or a market maker’s bid-ask spread.

It isn’t fixed

Standard −110/−110 is a round-number convention, not a law. Vig varies by:

  • Book. Some books run closer to the market (lower vig) to attract volume; others price wider, especially on markets they don’t want much action on.
  • Market type. Mainstream spreads and totals tend to run tighter. Player props, parlays and same-game parlays almost always carry a much heavier hold — often 10–20%+ — because the book has less competitive pressure and more model risk on those markets.
  • How lopsided the market is. A heavy favorite’s moneyline (e.g. −400) usually carries more vig in percentage terms than a near-even game.

Why this is worth tracking

Vig is the one cost in sports betting you pay on every single bet, win or lose, and it’s entirely visible before you place anything — unlike variance, which you can’t control, or a model’s edge, which you can’t directly observe. Two concrete things follow from that:

  • Shopping the same bet across multiple books is the most reliable way to personally reduce the vig you pay, because you’re simply picking the better of two already-built prices.
  • A market with unusually heavy vig deserves a higher bar before betting it — you’re giving up more ground before the game even starts.

Once you can see the vig in a market, the natural next step is stripping it out to see what the market actually believes the true probability is. That’s the no-vig fair price, covered next.