How Betting Odds Work

Betting odds do two jobs at once: they tell you how much a bet pays, and they reveal the implied probability the sportsbook assigns to an outcome. Learn to read all three common formats and you can compare prices instantly and spot when a line offers value. Here's how each works, with examples.

American odds explained

American odds use a plus or minus sign. A minus number (e.g. −150) shows how much you'd stake to win $100; a plus number (e.g. +130) shows how much you'd win on a $100 stake. The favorite carries the minus, the underdog the plus. Example: at −150, a $150 bet wins $100 (returns $250 total). At +130, a $100 bet wins $130 (returns $230 total).

Decimal and fractional odds

Decimal odds (e.g. 2.50) show your total return per $1 staked, including your stake, a $100 bet at 2.50 returns $250. Fractional odds (e.g. 6/4) show profit relative to stake, 6/4 means $6 profit for every $4 staked. All three formats describe the same probability, and most U.S. apps let you switch between them in settings.

Implied probability and the vig

Any odds can be converted into an implied probability, the chance the price suggests. −150 implies about 60%; +130 implies about 43%. Comparing implied probability to your own estimate is the core of finding value. Note that the book builds in a margin called the vig (or juice), so the implied probabilities on both sides of a market add up to more than 100%, that gap is the sportsbook's built-in edge.

Why lines differ between sportsbooks

Two sportsbooks can post different odds on the same game because each sets its own prices based on its risk and the bets it's taking. This is why many bettors hold accounts at multiple books and 'line shop' for the best available price, over time, consistently getting a better number meaningfully improves returns.