Understanding betting odds is absolutely essential if you are going to bet on sports online. Every single wager you place will have odds attached to it, and those odds determine exactly how much you stand to win or lose. If you cannot read and interpret odds you are flying blind, and that is no way to approach sports betting.

There are three odds formats you will encounter when placing bets online: American odds, decimal odds and fractional odds. American odds are the standard at sportsbooks in the United States and will usually be the default setting when you open a new account at a site like BetOnline. Decimal odds are the preferred format across Europe and much of the rest of the world. Fractional odds show up most often in horse racing and futures betting. Each format expresses the same information in a different way, so understanding all three will make you a more informed bettor no matter where you are placing your wagers.

American Odds

American odds are the most common format used in North America and the one you will see by default at most US-facing sportsbooks. They use a plus (+) or minus (-) sign in front of a number to tell you the relationship between your wager and a $100 benchmark.

Here is an example using a regular season NHL game:

New York Rangers +140
Ottawa Senators -160

The Rangers are the underdog in this game. The (+) tells you how much you would win on a $100 bet. At +140, a $100 wager on the Rangers would return $140 in profit plus your original $100 stake back, for a total payout of $240.

The Senators are the favorite. The (-) tells you how much you need to risk in order to win $100. At -160, you would need to wager $160 to win $100 in profit. Your total payout on a winning bet would be $260 ($160 stake + $100 winnings).

American odds are intuitive when betting on underdogs because the plus number immediately tells you your profit on a $100 bet. Where they get tricky is with favorites. Try to quickly calculate your winnings on a $200 bet at -165 odds. It is not easy to do in your head – the answer is $121.21. The formula is (wager / odds x 100), so ($200 / 165 x 100 = $121.21). For that reason, many bettors prefer to switch to decimal odds when they want to calculate exact payouts on favorites.

Decimal Odds

Decimal odds are the standard format across Europe, Australia and most international sportsbooks. If you check odds at a non-American betting site or use an odds comparison service you will almost certainly see decimal odds. They are arguably the easiest format to work with because finding your payout requires just one multiplication.

Here is the same Rangers vs Senators game expressed in decimal odds:

New York Rangers 2.40
Ottawa Senators 1.625

To find your total payout you simply multiply your wager by the decimal number. A $100 bet on the Rangers at 2.40 would return a total payout of $240 ($100 x 2.40). To find your profit you subtract the stake, so $240 – $100 = $140 in winnings. That matches the +140 American odds from the example above.

Decimal odds are especially handy when betting on favorites. With American odds you have to work backwards from the minus number to figure out your payout, but with decimal odds the math is the same regardless of whether the team is favored or not. A $100 bet on the Senators at 1.625 pays out $162.50, for a profit of $62.50. Any decimal odds below 2.00 indicate a favorite, while anything above 2.00 is an underdog. Odds of exactly 2.00 represent an even money bet.

Fractional Odds

Fractional odds are most commonly used in horse racing and futures markets where there are many possible outcomes. You will also see them used by UK bookmakers for standard sports betting. The format expresses your potential profit as a ratio of your stake.

Sticking with the same hockey game, the fractional odds would look like this:

New York Rangers 7/5
Ottawa Senators 5/8

The first number (numerator) is how much you win by betting the second number (denominator). So a $5 bet on the Rangers at 7/5 would win $7 in profit. A $8 bet on the Senators at 5/8 would win $5.

Fractional odds are very easy to read when they break down cleanly. A horse at 4/1 in the Kentucky Derby means a $100 bet wins $400. A longshot at 20/1 means a $100 bet wins $2,000. The format gets trickier when the fractions are less neat, like 11/4 or 15/8, because the math is no longer as quick in your head. That said, fractional odds are a natural fit for conversations about betting – it sounds better to say you took a fighter at 3/1 than to say you took them at +300 or 4.00.

Converting Between Odds Formats

Since all three formats express the same underlying probability, you can convert between them whenever you need to. Here are the basics.

To convert American odds to decimal: for a positive American line, divide by 100 and add 1. So +140 becomes (140 / 100) + 1 = 2.40. For a negative American line, divide 100 by the number and add 1. So -160 becomes (100 / 160) + 1 = 1.625.

To convert fractional odds to decimal: divide the numerator by the denominator and add 1. So 7/5 becomes (7 / 5) + 1 = 2.40.

You do not need to memorize these formulas. Most online sportsbooks let you toggle between odds formats in your account settings with a single click. But understanding the relationship between the formats will help you compare odds across different sites when you are shopping for the best lines, which is one of the smartest habits you can develop as a sports bettor.

Implied Probability

Beyond calculating payouts, odds also tell you something else that is just as valuable – the implied probability of an outcome. This is the percentage chance the odds suggest a team or player has of winning.

The easiest way to find implied probability is through decimal odds. Simply divide 1 by the decimal odds. For the Senators at 1.625, the implied probability is 1 / 1.625 = 0.615 or 61.5%. For the Rangers at 2.40, it is 1 / 2.40 = 0.417 or 41.7%.

You will notice those two percentages add up to more than 100%. The extra percentage is the sportsbook’s built-in edge, often called the vig or juice. Understanding implied probability helps you identify situations where you believe a team’s true chance of winning is higher than what the odds suggest, and that is the foundation of finding value in your bets over the long run. If you want to learn more about managing your wagers effectively, check out our bankroll management guide.