How Sportsbooks Make Money: The Vig Explained
People assume sportsbooks profit when bettors lose. That's not quite how it works. A well-run book doesn't care who wins any single game — it's built to make money no matter what, through a quiet little tax called the vig (short for vigorish, also called the juice). Understanding it is the first step to beating it.
What the vig actually is
Look at a typical point spread. Both sides are priced at −110 — you risk $110 to win $100 on either team. That ten-dollar surcharge is the vig.
Convert −110 to an implied probability and it's 52.4%. Price both sides at 52.4% and they add up to 104.8% — not 100%. That extra 4.8% is the book's margin, collected on every pair of bets.
The balanced book
In an ideal world, the book takes equal money on both sides of a game. Whoever wins, the losers' stakes pay the winners, and the book keeps the vig as pure profit — risk-free.
To keep things balanced, books move lines toward the public. If everyone's hammering the Lakers, the book shades the number to make the other side more attractive. They're not predicting the game — they're managing money. This is exactly why popular teams and favorites get overpriced, and it's the mechanism behind the true line: the book's number reflects betting behavior, not just the real probability.
How much the vig really costs you
That 4.8% sounds small. It isn't. Because of the vig, a −110 bettor has to win 52.4% of the time just to break even — not 50%. Coin-flip betting is a slow loss.
Stretch that across a season of hundreds of bets and the vig is the single biggest reason most bettors finish in the red. They're not necessarily bad at picking games; they're paying a toll on every ticket and never clearing it.
How to beat the vig
- Shop for the best number. One book's −105 beats another's −110. That's free margin, and over a season it's the difference between winning and losing.
- Only bet +EV. The vig is a fixed cost; the way to overcome it is to take prices that pay more than the true probability deserves. That's expected value.
- Fade the public side. Since books shade lines toward popular teams, the unpopular side is often where the value sits — the heart of finding mispriced lines.
Why a true line matters here
You can't beat the vig if you don't know what the fair price is. A true line strips out the juice and the public shading to show what each side should cost. Compare that to the book's number and you can see, instantly, which side is overpriced and which one pays you to take it.
That's the whole game at Dr. TrueLine: we publish the vig-free true line next to the book's line, flag the edges, and grade every result in public so you can see the math working over time.