How to Read Betting Odds: American, Decimal, and Fractional
Why Odds Format Matters
Sportsbooks in the United States typically display American odds (+150, -110), while European and international books use decimal (2.50) or fractional (3/2) formats. Understanding all three lets you shop lines across books and calculate your true implied probability on any bet.
American Odds
American odds are centered on $100. A positive number (+150) tells you how much profit you make on a $100 bet. A negative number (-110) tells you how much you must bet to profit $100.
- +150: Bet $100, profit $150. Total return: $250.
- -110: Bet $110, profit $100. Total return: $210.
- +100 (even money): Bet $100, profit $100.
Implied probability from American odds:
- Positive: 100 ÷ (odds + 100) — e.g. +150 → 100/250 = 40%
- Negative: |odds| ÷ (|odds| + 100) — e.g. -110 → 110/210 = 52.4%
Decimal Odds
Decimal odds represent your total return per $1 staked, including your original bet. They're the easiest format for calculating parlays — just multiply the decimals together.
- 2.50: Bet $100, total return $250 (profit $150). Implied probability: 1/2.50 = 40%.
- 1.91: Bet $110, total return $210 (profit $100). Implied probability: 1/1.91 = 52.4%.
Convert from American:
- Positive: (odds/100) + 1 → +150 = 2.50
- Negative: (100/|odds|) + 1 → -110 = 1.909
Fractional Odds
Fractional odds show profit relative to stake. 3/1 ("three to one") means profit $3 for every $1 staked. Common in UK horse racing.
- 3/1: Bet $100, profit $300. Total return $400. Implied probability: 1/(3+1) = 25%.
- 1/2: Bet $200 to profit $100. Implied probability: 2/(1+2) = 66.7%.
The Vig (Juice)
If you add up the implied probabilities on both sides of a bet, they always exceed 100%. That excess is the sportsbook's margin — called the vig or juice. A standard -110/-110 line has a combined implied probability of 104.8%, meaning the book keeps 4.8% as margin. Shopping for the best odds reduces the vig you pay. Use our Odds Converter to calculate implied probabilities quickly.