Definition
A balanced book means a sportsbook has roughly equal liability on both sides of a bet, so the result does not decide whether the book wins or loses money. The book earns from the vig built into the price.
For American odds, implied probability is:
negative odds / (negative odds + 100)
At -110, the implied probability is 110 / (110 + 100) = 52.38%. Two sides priced at -110 total 104.76%, which shows the bookmaker margin before removing vig.
Worked Example
A sportsbook posts both sides of an NFL spread at -110.
- Bettors risk
$1,100on Team A to win$1,000 - Bettors risk
$1,100on Team B to win$1,000
Total handle is $2,200.
If Team A covers, the book keeps the $1,100 lost on Team B and pays $1,000 profit to Team A bettors. Team A bettors also get their $1,100 stake back.
Book result: $1,100 - $1,000 = $100 profit.
The same $100 profit occurs if Team B covers.
Why It Matters
A balanced book explains why sportsbooks can profit without needing to predict the winner. For bettors, it helps separate market pricing from true probability, especially when comparing vig, no-vig lines, and whether a price has real edge.