How to Read Sports Betting Odds: American, Decimal, and Fractional Explained
Most people who lose money betting on sports do not lose because they picked the wrong team. They lose because they never fully understood what they were agreeing to when they placed the bet. Odds are the language of sports betting, and if you cannot read them fluently, you are at a disadvantage before the game even starts.
This guide breaks down the three main odds formats you will encounter — American, decimal, and fractional — explains how each one works, and shows you how to use them to calculate potential payouts and evaluate whether a bet is actually worth placing.
What Betting Odds Actually Tell You
Odds serve two purposes at once. They tell you how much you stand to win relative to how much you risk, and they reflect how likely the sportsbook thinks a given outcome is. Understanding both functions is important because a bet can look attractive on the payout side while being terrible on the probability side.
When a sportsbook sets a line, it is not simply guessing. Sharp bookmakers use statistical models, sharp bettor action, and market signals to price each outcome. The odds they post represent their best estimate of where the true probability lies — with a small margin built in for themselves. That margin is called the vig or the juice, and it is how sportsbooks make money regardless of who wins.
American Odds (Moneyline Format)
American odds are the default format at every major US sportsbook, including Bovada, BetOnline, MyBookie, and DraftKings. They are expressed as a number preceded by either a plus or a minus sign, and once you understand what those signs mean, reading them becomes second nature.
Negative Numbers: The Favorite
A negative number tells you how much you need to bet to win $100 in profit. The team or outcome with a negative line is the favorite.
For example, if the Kansas City Chiefs are listed at -180 on the moneyline, you must wager $180 to win $100. Your total return would be $280 — your $180 stake plus $100 in profit. The higher the negative number, the heavier the favorite, and the less value you get for your money.
Positive Numbers: The Underdog
A positive number tells you how much profit you would earn on a $100 bet. The team or outcome with a positive line is the underdog.
If the Cleveland Browns are listed at +155, a $100 bet returns $155 in profit, for a total payout of $255. You are being compensated for taking on more risk by backing the team less likely to win.
A Real-Game Example
Imagine an NFL game with the following lines:
- Dallas Cowboys: -220
- New York Giants: +185
To profit $100 on Dallas, you need to bet $220. To profit $185 on New York, you only need to bet $100. The Cowboys are the strong favorite, and the odds reflect that. If you believe the Giants have a real shot, the return on a smaller bet is considerably higher.
Decimal Odds
Decimal odds are common across Canada, Europe, Australia, and international sportsbooks. Some US books, including Bovada and BetOnline, allow you to switch your display to decimal format in account settings. They are arguably the most straightforward format to work with mathematically.
How Decimal Odds Work
The decimal number represents your total return per dollar wagered — including your original stake. To calculate your total payout, you simply multiply your bet by the decimal.
- Decimal of 2.50 on a $100 bet: $100 x 2.50 = $250 total return, or $150 in profit
- Decimal of 1.45 on a $100 bet: $100 x 1.45 = $145 total return, or $45 in profit
Any decimal below 2.00 means you are wagering on a favorite. Any decimal above 2.00 means you are backing an underdog. A decimal of exactly 2.00 represents an even-money bet.
Converting American to Decimal
If you are more comfortable with decimal odds but your sportsbook shows American lines, here is how to convert:
For positive American odds: divide by 100 and add 1. So +150 becomes (150/100) + 1 = 2.50.
For negative American odds: divide 100 by the absolute value and add 1. So -200 becomes (100/200) + 1 = 1.50.
Fractional Odds
Fractional odds are the oldest format in sports betting, still widely used in the United Kingdom and for horse racing worldwide. You may encounter them on international platforms or when betting on major racing events. They look like this: 5/1, 2/1, or 7/2.
How to Read Them
The number on the left is your profit, and the number on the right is your stake. So 5/1 means you win $5 for every $1 you bet. A $20 bet at 5/1 returns $100 in profit plus your $20 stake back, for a total of $120.
For odds like 7/2, divide the left by the right to find your profit ratio. 7 divided by 2 is 3.5, meaning you profit $3.50 for every dollar wagered. On a $100 bet, that is $350 in profit.
Fractions below 1/1 — such as 1/2 — indicate a heavy favorite. A bet at 1/2 means you risk $2 to profit $1.
When You Will See Fractional Odds
Most US sportsbooks do not display fractional odds by default, but they appear regularly in horse racing books and on platforms like Bookmaker.eu that cater to international audiences. If you are betting on the Kentucky Derby or international soccer futures, you may see them.
Implied Probability: The Most Useful Concept in Sports Betting
Beyond knowing your potential payout, the smartest bettors think in terms of implied probability. This is the probability that the odds suggest an outcome will occur. If you can identify when the implied probability is lower than the actual probability, you have found a value bet.
The Formula
For positive American odds: Implied probability = 100 / (odds + 100)
For negative American odds: Implied probability = |odds| / (|odds| + 100)
Using the NFL example from earlier:
- Dallas Cowboys at -220: Implied probability = 220 / (220 + 100) = 68.75%
- New York Giants at +185: Implied probability = 100 / (185 + 100) = 35.09%
Notice that 68.75% and 35.09% add up to more than 100%. That extra percentage — roughly 3.84% in this case — is the sportsbook’s built-in margin. It exists on nearly every market and is why the house always has a mathematical edge.
Why This Matters for Your Betting Decisions
If you assess that the Giants have a 42% chance of winning but the odds only imply 35%, you have identified value. Consistently finding and acting on that gap is how professional bettors make money over the long run. Betting at random, or based purely on team loyalty, means you are likely paying for the vig without any edge to offset it.
Point Spreads and Totals: Odds in Context
The moneyline is not the only way odds are presented. Two other common bet types use odds as part of a structured market.
Point Spread Betting
The point spread is a margin of victory the sportsbook assigns to even out two mismatched teams. The favorite must win by more than the spread for a bet on them to pay out, and the underdog either wins outright or loses by less than the spread.
Most spread bets in the NFL and NBA are priced at -110 on both sides. This means you bet $110 to win $100 no matter which side you take. That -110 price — rather than an even 1/1 or 2.00 decimal — is the vig. Both sides pay slightly less than true even money, and the sportsbook earns its margin on the difference.
Totals Betting (Over/Under)
A totals bet asks whether the combined score of both teams will go over or under a number set by the sportsbook. Like spread betting, most totals are priced at -110 on both sides. The logic is the same: the book earns its cut regardless of which way the total falls.
Line Shopping: Using Odds Knowledge to Your Advantage
One of the most practical applications of understanding odds is line shopping — the practice of comparing lines across multiple sportsbooks before placing a bet.
Even small differences in odds add up significantly over time. A bettor who consistently gets +155 instead of +140 on underdog picks, or -105 instead of -115 on spread bets, is gaining a meaningful edge without doing anything exotic.
Sportsbooks like BetOnline, Bovada, and MyBookie all post slightly different lines on the same games, particularly in the first 24 hours after lines open. Keeping accounts at two or three books and checking each before you bet is one of the simplest ways to improve your long-term results.
FAQ
- What does -110 mean on a spread bet?
- How do I know if a bet has good value?
- What is the difference between the moneyline and the spread?
- Why do odds change before a game?
- Can I always use the same formula to calculate payouts?
The Bottom Line
Reading odds accurately is the first skill any serious bettor needs to develop. It is not complicated, but it does require moving past the surface-level read of who is favored and starting to think about what the odds actually imply about probability and value.
Once you are comfortable with American, decimal, and fractional formats — and once you understand implied probability — you will be in a position to make better decisions at every step of the betting process, from choosing which markets to play to which sportsbook offers the best price on a given game.
If you are ready to put this into practice, compare the top-rated sportsbooks on XSportsbook.com/Reviews to find the platform that best fits your betting style.
