Understanding Sports Betting Odds: American, Decimal, and Fractional

Odds are the language of sports betting. They tell you how much you can win, but more importantly, they tell you what probability the market is assigning to an outcome. Once you can read and convert all three common formats, you can compare prices anywhere and judge whether a bet offers value.

American odds

American odds, also called moneyline odds, are standard in the United States. They use a plus or minus sign around a base of 100.

• Positive odds (+150) show how much profit you make on a $100 stake. A $100 bet at +150 returns $250: your $100 back plus $150 profit.
• Negative odds (−150) show how much you need to stake to make $100 profit. You risk $150 to win $100, for a total return of $250.

A plus sign usually marks the underdog and a minus sign the favorite. Even money is written as +100.

Decimal odds

Decimal odds are common in Europe, Canada and Australia, and they are the easiest to work with. The number shows your total return per unit staked, including your stake.

At 2.50, a $100 bet returns $250, which is $150 profit. At 1.67, a $100 bet returns $167. Anything above 2.00 pays more than even money; anything below pays less.

Fractional odds

Fractional odds are traditional in the UK and Ireland, especially in horse racing. They show profit relative to stake.

At 3/2, you win $3 for every $2 staked, so a $100 bet returns $150 profit plus your $100. At 1/2, you win $1 for every $2 staked. Evens, or 1/1, means you win the same amount you stake.

The same price in all three formats

• −200 = 1.50 = 1/2
• −150 = 1.67 = 2/3
• −110 = 1.91 = 10/11
• +100 = 2.00 = evens
• +150 = 2.50 = 3/2
• +300 = 4.00 = 3/1

How to convert odds

American to decimal

• Positive: decimal = 1 + (American ÷ 100). Example: +150 becomes 1 + 1.5 = 2.50.
• Negative: decimal = 1 + (100 ÷ the number without the minus sign). Example: −150 becomes 1 + 0.667 = 1.67.

Decimal to American

• If decimal is 2.00 or more: American = (decimal − 1) × 100. Example: 2.50 becomes +150.
• If decimal is below 2.00: American = −100 ÷ (decimal − 1). Example: 1.50 becomes −200.

Fractional to decimal

• Decimal = (numerator ÷ denominator) + 1. Example: 3/2 becomes 1.5 + 1 = 2.50.

Implied probability

Every price implies a probability. If you think the true probability is higher than the implied one, the bet may offer value.

• Decimal: implied probability = 1 ÷ decimal odds. At 2.50, that is 40%.
• Positive American: 100 ÷ (odds + 100). At +150, 100 ÷ 250 = 40%.
• Negative American: odds ÷ (odds + 100), using the number without the minus sign. At −150, 150 ÷ 250 = 60%.
• Fractional: denominator ÷ (numerator + denominator). At 3/2, 2 ÷ 5 = 40%.

Spotting the bookmaker’s margin

Add up the implied probabilities for every outcome in a market. In a perfectly fair market, they would total 100%. In reality, they total more, and the excess is the bookmaker’s margin, often called the vig or juice.

Take a typical point spread priced at −110 on both sides. Each side implies about 52.4%, so the total is about 104.8%. That extra 4.8% is the overround. To estimate the fair probability for each side, divide each implied probability by the total: 52.4% ÷ 104.8% = 50%.

Removing the margin this way, often called “no-vig” pricing, is how sharp bettors compare their own estimates against the market.

Break-even win rates

The implied probability of your odds is also your break-even win rate. At −110, you need to win about 52.4% of your bets to break even. At +150, you only need to win 40%. That is why judging a bettor by win rate alone is misleading: someone winning 45% of +150 bets is doing far better than someone winning 52% of −110 bets.

Why this matters in a funded challenge

BetFunder challenges simulate results using real-time odds from established sportsbooks, so every pick you make is priced exactly as described here. Understanding odds helps you in three ways:

• You know your break-even win rate at the prices you typically bet.
• You can judge whether a price offers value before you place a pick.
• You can track whether you are beating the closing line, a key sign of a sustainable edge.

Next, put implied probability to work with our guide to expected value.

BetFunder challenges use virtual Profit Points and are available only to people who meet our eligibility requirements. Only spend what you can afford on a challenge fee. If betting stops being fun, visit our Responsible Gambling page.