Odds do two jobs at once: they tell you what a winning bet pays, and they express how likely the sportsbook thinks an outcome is. Learning to read all three formats is worth the effort because offshore and international books often default to decimal, US books to American, and horse racing to fractional. They all describe the same thing.
The Three Formats
American (moneyline) odds
American odds are anchored to $100. A favorite carries a minus sign showing how much you must risk to win $100; an underdog carries a plus sign showing how much a $100 stake wins. So -200 means risk $200 to win $100, and +150 means risk $100 to win $150. The bigger the negative number, the heavier the favorite.
Decimal odds
Decimal odds show your total return per $1 staked, including your stake back. A price of 2.50 returns $2.50 for every $1 (a $1.50 profit plus your $1). To find profit, subtract 1. Decimal is the easiest format for parlays because you simply multiply the legs together.
Fractional odds
Fractional odds, common in the UK and in racing, show profit relative to stake. 5/1 ("five to one") pays $5 profit for every $1 risked; 1/2 pays $1 profit for every $2 risked. To convert a fraction to decimal, divide it out and add 1: 5/1 becomes 6.00, and 1/2 becomes 1.50.
Conversion Table
Here is how the same handful of prices look across all three formats, with the implied probability each one carries.
| American | Decimal | Fractional | Implied Probability |
|---|---|---|---|
| -200 | 1.50 | 1/2 | 66.67% |
| -150 | 1.67 | 2/3 | 60.00% |
| -110 | 1.91 | 10/11 | 52.38% |
| +100 | 2.00 | 1/1 | 50.00% |
| +150 | 2.50 | 3/2 | 40.00% |
| +200 | 3.00 | 2/1 | 33.33% |
| +500 | 6.00 | 5/1 | 16.67% |
The Conversion Math
American to decimal
For a positive price, divide by 100 and add 1: +150 becomes (150 / 100) + 1 = 2.50. For a negative price, divide 100 by the number and add 1: -110 becomes (100 / 110) + 1 = 1.91.
Decimal to American
If the decimal is 2.00 or higher, subtract 1 and multiply by 100: 2.50 becomes (2.50 - 1) x 100 = +150. If it is below 2.00, take -100 divided by (decimal - 1): 1.50 becomes -100 / 0.50 = -200.
Implied probability
The cleanest route is through decimal: implied probability equals 1 divided by the decimal odds. A decimal of 2.50 implies 1 / 2.50 = 40%. For -110, 1 / 1.909 = 52.38%. This number is the key to everything, because it tells you the win rate you need just to break even.
Where the Vig Hides
Add up the implied probabilities on both sides of a market and you will get more than 100%. On a standard spread with both sides at -110, that is 52.38% + 52.38% = 104.76%. The 4.76% overround is the vig, the sportsbook's margin. To find your true break-even chance, you can remove the vig by dividing each side's implied probability by the total; here, 52.38% / 104.76% = a fair 50%.
This is why line shopping pays. A book offering -105 instead of -110 lowers the implied probability you need to beat, and over hundreds of bets that edge compounds. If you understand implied probability, you can spot when a price is generous. See how this feeds into multi-leg tickets in our parlay betting guide.
Why odds move
The number you see is not fixed. Odds shift between the moment a market opens and kickoff for two main reasons. The first is new information: an injury, a lineup change, weather, or a goalie confirmation forces the book to reprice. The second is betting action: when money piles onto one side, the book adjusts the line to balance its liability and to respect the signal from sharp bettors. A line that moves from -3 to -3.5 despite no news often reflects respected money coming in. Reading these movements is a skill in itself, and it starts with being fluent in what each price implies.
Favorites, Underdogs, and Value
A common beginner mistake is assuming favorites are "safer" bets and therefore better. They are more likely to win, but you pay for that likelihood in the price. A -200 favorite wins two out of three times on paper, yet you only profit $50 on a $100 stake, so a single loss erases two wins. Conversely, a +200 underdog loses two-thirds of the time but pays $200 when it hits. Neither is inherently better; value is the only thing that matters. Value exists when the true probability of an outcome is higher than the implied probability baked into the price. Your entire job as a bettor is to find those gaps, and that requires reading odds fluently, which is exactly what implied probability lets you do.
Putting It Together
When you see +150 on an underdog, translate instantly: 2.50 decimal, 3/2 fractional, 40% implied. Then ask the only question that matters: do you think the real chance of that outcome is higher than 40%? If yes, you have found value. If not, pass. New York's licensed mobile books and the offshore books we review, such as BetOnline, all display odds in these formats, and most let you toggle between them in the settings.