How do betting odds work?
Betting odds are a price. They tell you what a bet pays and, read the other way, how often it has to win. Odds of -200 mean you risk $200 to win $100. Odds of +150 mean you risk $100 to win $150.
Minus and plus
American odds hang on the number 100. A minus price belongs to the favorite, and the number is what you have to risk to win $100, so at -200 you put up $200 to win $100, or $20 to win $10. A plus price belongs to the underdog, and the number is what you win when you risk $100: at +150, $100 wins $150 and $20 wins $30. Either way a winner gets the stake back with the winnings, which is why a $200 bet at -200 returns $300.
That is all there is to reading them. The useful part is what comes next.
Every price is a percentage
Divide what you risk by what you get back in total, and you have how often the bet has to win for you to break even. At -200 you risk 200 to get back 300, which is 66.67 percent. At +150 you risk 100 to get back 250. That is 40 percent. At -110, the usual price on a point spread, it comes to 52.38 percent.
I do that sum before every bet, and I'd tell anyone to do the same (it is short division, nothing more). Once the price is a percentage, the question stops being whether you like the team and becomes whether the team wins more often than the number says, which is a question you can actually work on. The implied probability page goes through it in full.
Where the book keeps its cut
Take a game priced -200 on the favorite and +170 on the underdog. The favorite's price says 66.67 percent and the underdog's says 37.04, and when you add them you get 103.7, which is odd, because two teams can only share 100 between them. The extra 3.7 is the vig. It is the book's charge for taking the bet, and I never saw a book leave it out.
The same price, three ways
| American | Decimal | Fractional |
|---|---|---|
| -200 | 1.50 | 1/2 |
| -110 | 1.91 | 10/11 |
| +150 | 2.50 | 3/2 |
Decimal odds show the total return on each $1 staked, and fractional odds show the winnings over the stake. Books outside the US mostly use one of those two. The bet is the same whichever way it is written, and the guide on how to read odds covers each format.
Two habits are worth more than knowing every format. Look at the same game at a second book, because the price is often a few cents different and those cents cost you nothing to find. And settle the stake before you look at the payout: most professionals keep any one bet under 5 percent of their bankroll, and I'd stay well inside that.
The odds don't tell you who wins. They tell you what it costs to have an opinion.
Related questions
What does moneyline mean?
A moneyline is a bet on which team wins the game, with no point spread. The favorite has a minus price and the underdog a plus price. At -150 you risk $150 to win $100. At +130 you risk $100 to win $130.
How do bookies make money?
A bookie makes money by charging for every bet. The charge is built into the price: you lay $110 to win $100, and across thousands of bets that extra $10 is his living. He does not need to pick winners. He needs volume.
What is a parlay?
A parlay is one bet made of two or more picks. Every pick has to win for the ticket to pay, and the payout multiplies with each one you add. Miss one and the whole ticket loses.