Sportsbooks display odds in different formats: American (moneyline), decimal, and fractional. Knowing how to convert between them helps you compare lines, calculate parlay payouts, and understand implied probability. This guide gives you the formulas and worked examples.
For instant conversion, use our Odds Converter. For context on reading odds, see our betting guides.
Why understanding multiple odds formats matters
Different regions and books use different formats. American odds dominate in the U.S.; decimal is standard in Europe, Australia, and many online books; fractional is common in the UK. If you're comparing lines across books or calculating parlays, you need to speak every format.
- Line shopping: Compare -110 vs 1.91 vs 10/11 across books.
- Parlay math: Decimal multiplication is easiest; convert first, then multiply.
- Implied probability: Same concept in every format—different formulas.
American odds explained (positive and negative)
American odds (moneyline format) use positive and negative numbers based on a $100 unit.
- Negative (favorite): -150 means you risk $150 to win $100 profit. Total return = $250 on a $150 bet.
- Positive (underdog): +200 means you risk $100 to win $200 profit. Total return = $300 on a $100 bet.
Negative odds = favorite (more likely to win). Positive odds = underdog (less likely to win).
Decimal odds explained
Decimal odds show your total return per $1 staked, including stake.
Example: 2.50 means for every $1 you bet, you get $2.50 back (so $1.50 profit). It's the simplest format for multiplication—ideal for parlays and parlay calculators.
Fractional odds explained
Fractional odds (e.g., 5/2, 1/3) show profit relative to stake.
- 5/2 = profit of 5 for every 2 staked → total return 7 for 2 staked
- 1/3 = profit of 1 for every 3 staked → total return 4 for 3 staked
Common in UK and horse racing. To get decimal: divide numerator by denominator, add 1. So 5/2 → (5÷2)+1 = 3.50.
Converting American to decimal (formula + 3 examples)
Formula:
- Negative American: Decimal = 1 + (100 ÷ |American|)
- Positive American: Decimal = 1 + (American ÷ 100)
Example 1: -150 → 1 + (100/150) = 1 + 0.667 = 1.667
Example 2: +175 → 1 + (175/100) = 1 + 1.75 = 2.75
Example 3: -110 → 1 + (100/110) = 1 + 0.909 = 1.909
Converting decimal to American (formula + 3 examples)
Formula:
- If decimal > 2.00: American = (Decimal - 1) × 100 (positive)
- If decimal < 2.00: American = -100 ÷ (Decimal - 1) (negative)
Example 1: 2.75 > 2 → (2.75 - 1) × 100 = +175
Example 2: 1.50 < 2 → -100 ÷ (1.50 - 1) = -100 ÷ 0.50 = -200
Example 3: 1.909 < 2 → -100 ÷ (1.909 - 1) = -100 ÷ 0.909 ≈ -110
Converting to fractional (formula + examples)
Easiest path: convert to decimal first, then to fractional.
Decimal to fractional: Write (Decimal - 1) as a fraction, then simplify. Decimal 2.50 → 1.50 = 3/2. Decimal 1.667 → 0.667 ≈ 2/3 (or 667/1000 simplified).
American to fractional: Convert American → decimal → fractional.
- +200 → 3.00 → (3-1) = 2/1
- -200 → 1.50 → (1.50-1) = 0.50 = 1/2
- -110 → 1.909 → 0.909 ≈ 10/11
Use our free Odds Converter for instant results.
Implied probability from any format (formulas)
Implied probability = what the odds suggest the chance of winning is (including vig).
From decimal: Implied % = (1 ÷ Decimal) × 100
- 2.00 → 50%
- 1.50 → 66.7%
- 3.00 → 33.3%
From American:
- Negative: Implied % = |American| ÷ (|American| + 100) × 100. -150 → 150/250 = 60%
- Positive: Implied % = 100 ÷ (American + 100) × 100. +200 → 100/300 = 33.3%
From fractional (a/b): Implied % = b ÷ (a + b) × 100. 5/2 → 2/7 ≈ 28.6%
When to use each format
- American: U.S. sportsbooks, moneylines, quick "favorite vs underdog" read.
- Decimal: International books, parlay math, parlay payouts, and payout calculations.
- Fractional: UK books, horse racing, traditional betting slips.
When in doubt, convert everything to decimal. It's the cleanest for math and comparison.
Use the right tools
Converting by hand is useful for understanding, but tools save time:
- Odds Converter – Convert American, decimal, fractional, and see implied probability.
- Parlay Calculator – Enter legs in any format, get combined decimal and payout.
- Payout Calculator – Check single-bet and parlay payouts.
- Schedule – View games and odds in context.
Try our free Odds Converter to convert between American, decimal, and fractional in seconds.
FAQ
How do you convert American odds to decimal?
Negative American: Decimal = 1 + (100 ÷ |odds|). Positive American: Decimal = 1 + (odds ÷ 100). Example: -150 → 1.667; +200 → 3.00.
How do you convert decimal odds to American?
If decimal > 2: American = (Decimal - 1) × 100 (positive). If decimal < 2: American = -100 ÷ (Decimal - 1) (negative). Example: 2.50 → +150; 1.50 → -200.
What is implied probability?
Implied probability is the win chance the odds suggest, including the book's margin. From decimal: (1 ÷ decimal) × 100. From American negative: |odds| ÷ (|odds| + 100) × 100.
Why do sportsbooks use different odds formats?
Regional tradition (U.S. vs UK vs Europe) and user preference. American books default to moneyline; international sites often use decimal. Understanding both helps when line shopping.
What format is best for calculating parlay payouts?
Decimal. Parlay odds = multiply each leg's decimal odds. Convert American or fractional to decimal first, multiply, then convert back if needed. Use our Parlay Calculator for instant results.
Where can I find a free odds converter?
SportBusy offers a free Odds Converter that converts American, decimal, and fractional odds and displays implied probability. No sign-up required.