Betting odds tell you two things at once: how much a bet pays, and how likely the book thinks the result is. Once you can read both, every price on the board makes sense, whatever format it is written in.
There are three formats. US sportsbooks show American odds, decimal odds are standard in continental Europe, Australia and Canada, and fractions are still the norm in the UK, Ireland and horse racing. They are the same price written three ways.
American odds: the plus and the minus
American odds are built around $100. A plus number is what a $100 bet wins: +150 wins $150. A minus number is what you have to risk to win $100: -110 means risking $110 to win $100. Plus marks the underdog, minus marks the favorite, and +100 is even money.
Smaller stakes scale the same way. At +150 a $10 bet wins $15. At -110 a $10 bet wins $9.09. In both cases you also get your $10 back.
Decimal odds
A decimal price is the total you get back for every $1 staked, stake included. At 2.50 a $10 bet returns $25: $15 of profit plus the $10. Anything above 2.00 is an underdog price and anything below 2.00 is a favorite. Decimals are the easiest format for math, because a parlay's price is just the decimals of its legs multiplied together.
Fractional odds
A fraction is profit over stake. 3/2 means you win $3 for every $2 risked, which is the same as +150 and 2.50. 5/2 wins $5 for every $2 (+250, 3.50), and 1/2 wins $1 for every $2 risked (-200, 1.50).
| American | Decimal | Fractional | Implied chance |
|---|---|---|---|
| -400 | 1.25 | 1/4 | 80.0% |
| -200 | 1.50 | 1/2 | 66.7% |
| -110 | 1.91 | 10/11 | 52.4% |
| +100 | 2.00 | 1/1 (evens) | 50.0% |
| +150 | 2.50 | 3/2 | 40.0% |
| +250 | 3.50 | 5/2 | 28.6% |
| +300 | 4.00 | 3/1 | 25.0% |
Converting between formats
- American plus to decimal: divide by 100 and add 1. +150 becomes 1.5 + 1 = 2.50.
- American minus to decimal: divide 100 by the number and add 1. -200 becomes 0.5 + 1 = 1.50.
- Decimal to American: at 2.00 or more, subtract 1 and multiply by 100 (2.50 becomes +150). Under 2.00, divide -100 by the decimal minus 1 (1.80 becomes -125).
- Fraction to decimal: divide the top by the bottom and add 1. 5/2 becomes 2.5 + 1 = 3.50.
Implied probability: what the price expects
Every price can be turned into the win chance it implies. With decimal odds it is simply 1 divided by the price: 1 / 2.50 = 40%. With American odds, a minus price is the number divided by the number plus 100 (110 / 210 = 52.4%), and a plus price is 100 divided by the number plus 100 (100 / 250 = 40%).
This is the most useful number on the page. A price is a good bet only if you believe the result happens more often than its implied chance, and a bet that feels likely can still be priced too short.
The vig: why both sides add up to more than 100%
Spreads and totals are usually priced at -110 on both sides. Each side implies 52.4%, so the two together add up to 104.8%. Those extra 4.8 points are the book's built-in margin, known as the vig, the juice or the overround. Measured against all the money bet on a market balanced at -110 both ways, the book keeps about 4.5%.
- Break-even win rate at -110
- 52.4%
- Both sides at -110
- 104.8%
- Even money, +100
- 50.0%
of bets, just to finish level
4.8 points over 100 is the margin
a fair coin-flip price
The margin is also why you can compare books: the same game priced -105 on both sides instead of -110 adds up to 102.4%, a smaller cut. Over a season of bets, that difference is real money.
Reading a line on the board
A game listing usually shows three markets side by side. Here is a typical football line, with each part spelled out:
- Spread: Favorite -3.5 (-110), Underdog +3.5 (-110). The favorite has to win by 4 or more for the -3.5 side to win, and either side costs $110 to win $100.
- Total: 47.5, Over -110 and Under -110. A bet on whether the two teams' combined points finish above or below 47.5.
- Moneyline: Favorite -175, Underdog +150. A bet on the winner alone, priced in American odds.
Each of those prices runs through the same math: -110 needs a 52.4% win rate, -175 needs 63.6% and +150 needs 40%. Same game, three questions, three prices to judge.
The same numbers drive every bet type. See them at work in how the moneyline works and how parlay payouts multiply.