How Sports Betting Odds Work: American, Decimal and Fractional

By 4Football Staff · September 21, 2026 · 9 min read

A plain guide to reading and converting the three odds formats, American, decimal and fractional, with worked payout examples, a conversion table and the idea of implied probability.

You open an odds page for a football game and see a column of numbers: -150, +130, -110. A friend from the United Kingdom talks about a price of 5/2. A European site lists the same game at 2.60. Are these three different bets, or three different ways to write the same thing?

They are three ways to write the same thing. Odds are a language for describing two facts at once: how much a wager pays if it wins, and how likely the market thinks the result is. American, decimal and fractional odds all carry the same information, but they express it differently, and each is the standard in a different part of the world. This guide teaches you to read all three, convert between them and use them to find the probability behind a price. It is education about how the numbers work, not advice to place any wager.

What odds are telling you

Every set of odds does two jobs.

1. It states the payout. If you stake a certain amount and the outcome happens, the odds tell you how much you receive.
2. It implies a probability. A short price, which pays little, means the market considers the outcome likely. A long price, which pays a lot, means it considers the outcome unlikely.

Odds also include a margin for the company offering them. That margin, called the vig or juice, is why the probabilities implied by two sides of a market add up to slightly more than one hundred percent. We cover it in our guide to understanding the vig. For now, keep the idea in mind: a price is a mix of probability and a fee.

A stake is the amount you wager. The profit is what you win beyond the stake. The return (sometimes called the payout) is the profit plus the stake. Confusion between profit and return is the most common source of mistakes with odds, so we will keep the terms separate.

American odds

American odds, also called moneyline odds, are the standard in the United States. They use a positive or negative number and are built around a stake of 100 units.

Negative odds: the favorite

A negative number tells you how much you must stake to make a profit of 100. At -150, you stake 150 to win 100. If you stake less or more, the profit scales in proportion.

• Stake 150 at -150 and win: profit 100, return 250.
• Stake 75 at -150 and win: profit 50, return 125.
• Stake 15 at -150 and win: profit 10, return 25.

Positive odds: the underdog

A positive number tells you how much profit you make on a stake of 100. At +130, a stake of 100 earns a profit of 130.

• Stake 100 at +130 and win: profit 130, return 230.
• Stake 50 at +130 and win: profit 65, return 115.
• Stake 10 at +130 and win: profit 13, return 23.

The even-money point

Odds of +100, often written as "even" or "EVEN," pay profit equal to the stake. A -100 price means exactly the same thing. This is the dividing line: negative numbers describe prices shorter than even, and positive numbers describe prices longer than even.

A common mistake is to read -150 as a loss or as "minus 150 dollars." It is just a notation for the favorite side. Another is to think +130 is twice as good as -130. The two are not mirror images, because -130 means staking 130 to profit 100, while +130 means staking 100 to profit 130.

Decimal odds

Decimal odds are used across much of Europe, Canada, Australia and elsewhere. They are the simplest to calculate with. A decimal price tells you the total return for each unit staked, including the stake.

• At 2.60, a stake of 10 returns 26 if it wins, which means a profit of 16.
• At 1.50, a stake of 10 returns 15, a profit of 5.
• At 1.91, a stake of 10 returns 19.10, a profit of 9.10.

To find the return, multiply the stake by the decimal price. To find the profit, subtract the stake. Because decimal odds include the stake, the lowest possible price is just above 1.00, which would return almost exactly the stake. A price of 2.00 is even money.

Fractional odds

Fractional odds are traditional in the United Kingdom and Ireland, especially in horse racing. They are written like 5/2 and read "five to two." The first number is the profit and the second is the stake.

• At 5/2, a stake of 2 earns a profit of 5. A stake of 10 earns a profit of 25.
• At 1/2, a stake of 2 earns a profit of 1. This is a short price, a favorite.
• At 1/1, written "evens," a stake of 1 earns a profit of 1.

The fraction for an odds-on favorite has a larger bottom number than top number, such as 2/5 or 1/3. A price like 10/1 pays a profit of 10 for each 1 staked. A fraction can look odd, such as 10/11, but it works the same way: stake 11 to win 10.

Converting between the formats

Because all three formats express the same thing, you can convert from one to another. Here is a table of common prices.

The implied probability in the last column comes from a formula we explain below.

From American to decimal

• For a positive number, divide it by 100 and add 1. So +150 becomes 150 / 100 + 1 = 2.50.
• For a negative number, divide 100 by the number without its minus sign and add 1. So -150 becomes 100 / 150 + 1 = 1.67.

From decimal to American

• If the decimal price is 2.00 or more, subtract 1 and multiply by 100. So 3.00 becomes +200.
• If it is under 2.00, divide 100 by the decimal price minus 1, and put a minus sign in front. So 1.50 becomes 100 / 0.50 = -200.

From fractional to decimal

Divide the top number by the bottom number and add 1. So 5/2 becomes 2.5 + 1 = 3.50. Then you can convert to American if you wish: 3.50 is +250.

Going back to the opening example, a price of 5/2 in the United Kingdom, 3.50 in Europe and +250 in the United States are all the same price.

Implied probability

Any price can be turned into the probability it suggests. The formulas are short.

• Negative American odds: the number without its sign, divided by itself plus 100. For -150: 150 / (150 + 100) = 0.60, or 60 percent.
• Positive American odds: 100 divided by the number plus 100. For +130: 100 / (130 + 100) = 0.435, or about 43.5 percent.
• Decimal odds: 1 divided by the price. For 2.60: 1 / 2.60 = 0.385, or about 38.5 percent.
• Fractional odds: the bottom number divided by the sum of both numbers. For 5/2: 2 / (2 + 5) = 0.286, or about 28.6 percent.

Implied probability tells you how likely an outcome must be for a bet at that price to break even over the long run. If you accept a -150 price, you need to win more than 60 percent of the time for it to pay off. The topic deserves more attention than we can give it here, and our guide to implied probability works through it.

Notice that implied probability is not the same as the true probability. It is the probability the price suggests, with the company's margin built in. Two sides of a game priced at -110 each imply about 52.4 percent apiece, which totals about 104.8 percent. The extra 4.8 points is the margin.

One hypothetical game in all three formats

Here is a fully worked example, using an imaginary game between Team X and Team Y. No real teams are involved and the prices are chosen for easy arithmetic.

Suppose someone stakes 20 on Team X and Team X wins. At -200 the profit is 10 (they stake 200 to win 100, so 20 wins 10), and the return is 30. In decimal, the same result is 20 multiplied by 1.50, which is 30. In fractional, 1/2 means 1 of profit for every 2 staked, so 20 earns 10. All three agree.

Now suppose someone stakes 20 on Team Y and it wins. At +170, a stake of 100 earns 170, so 20 earns 34, and the return is 54. In decimal, 20 multiplied by 2.70 is 54. In fractional, 17/10 means 17 of profit for every 10 staked, so 20 earns 34. Again they agree.

Finally, add the two implied probabilities: 66.7 plus 37.0 is 103.7 percent. If the market were free of any margin, the total would be exactly 100. The extra 3.7 points is the cost built into the prices. If you understand this one table, you understand the foundation of the subject.

Rounding, ticks and small differences

You may notice that prices rarely look like the clean numbers in a textbook. A standard American price of -110 is exactly 1.909090... in decimal, and an odds display will round it to 1.91. That tiny rounding difference does not matter for a single wager. Two sites may show 1.91 and 1.90 for what looks like the same price, either because one rounds differently or because their prices genuinely differ slightly. Most books publish prices in steps (often called ticks) such as -105, -110, -115 and so on, and a move of one step changes the implied probability by only a small amount. Learning to see how much a step is worth is part of reading odds fluently.

It also explains why shopping among different providers can make a difference. Comparing prices across providers is a common topic in betting education, and the arithmetic of small differences is worth understanding even if you never place a wager.

The three common football markets

Football odds appear in a few standard forms, and the odds formats above apply to all of them.

Moneyline

A moneyline bet is on which team wins the game, regardless of the margin. The favorite has a negative price and the underdog has a positive one. A game between a strong team and a weak team might show -300 for the favorite and +250 for the underdog.

Point spread

A spread makes the sides more even by giving the underdog a head start. If a team is a 3.5-point favorite, it must win by four or more for a bet on it to succeed, while a bet on the underdog succeeds if the underdog wins or loses by three or fewer. Both sides usually carry a price near -110 in American odds. The standard price on a spread is why -110 appears so often.

Totals

A total, or over/under, is a bet on the combined score of both teams. You wager that the total will be above or below a number set by the oddsmaker. Our guide to over/under totals explains them in detail.

You will find all of these displayed in a table on our odds page, and we cover how to read one in the article on how to read an odds board.

To practice, open a game from the schedule, find its prices on the odds page, and convert each one into the other two formats. Afterward, compare your numbers with the final result on the scores page to see how often the favorite, the price and the outcome line up.

Common mistakes when reading odds

• Mixing up profit and return. A price of 2.60 returns 2.60 for each unit staked, which is a profit of 1.60.
• Treating a favorite as a guarantee. A price of -300 implies about 75 percent, which means the other outcome happens about one time in four.
• Reading positive odds as better. A +150 price is not better than -150. It is simply a different kind of price, and its value depends on the true probability.
• Forgetting the margin. The implied probabilities of all outcomes add up to more than one hundred percent.
• Comparing formats directly. A 2.50 price and a +150 price are the same, but a person unfamiliar with conversions may think they are different.
• Assuming a price never changes. Odds move as information and money arrive. The reasons range from injury news to the amount of money arriving on each side.

A note on legality and responsible play

Sports betting is legal only in some places, and only for adults who have reached the legal age where they live. Understanding odds does not make wagering safe or profitable, and every wager carries a risk of loss. If you or someone you know is concerned about gambling, the National Problem Gambling Helpline is available at 1-800-GAMBLER. Nothing here is a recommendation to bet, and the examples are chosen to teach arithmetic, not to suggest any wager.

The short version

• American odds use a base of 100: a negative number is the stake needed to win 100, and a positive number is the profit on a stake of 100.
• Decimal odds give the total return per unit staked, stake included.
• Fractional odds give profit over stake, such as 5/2.
• All three can be converted, so +250, 3.50 and 5/2 are the same price.
• Implied probability shows how often an outcome must occur to break even at a given price.
• Prices include a margin, so the implied probabilities of all outcomes add up to more than one hundred percent.