Understanding Odds
How to read American, Decimal, and Fractional odds.
Odds are the language of sports betting. They tell you two things: how much you can win and the implied probability of that outcome. Master reading odds, and you'll instantly understand any betting line.
Three Odds Formats
The same probability can be expressed three ways:
Same Odds, Different Formats
| American | Decimal | Fractional | Meaning |
|---|---|---|---|
| +150 | 2.50 | 3/2 | Bet $100, win $150 |
| -150 | 1.67 | 2/3 | Bet $150, win $100 |
| +100 | 2.00 | 1/1 | Bet $100, win $100 |
American Odds (Moneyline)
Most common in the US. Based on $100 bets.
Positive Numbers (+)
Show profit on a $100 bet:
Underdog. You risk $100 to win $250.
Negative Numbers (-)
Show how much to bet to win $100:
Favorite. You risk $175 to win $100.
Decimal Odds
Common in Europe and Australia. Shows total return per $1 bet.
Multiply your stake by the decimal to get total return.
Strategy Insight
Fractional Odds
Traditional UK format, especially for horse racing. Shows profit relative to stake:
- 5/1 = Win $5 for every $1 bet
- 1/4 = Win $1 for every $4 bet
- 11/8 = Win $11 for every $8 bet
Converting Between Formats
Good to Know
- Positive: (American ÷ 100) + 1
- Negative: (100 ÷ |American|) + 1
Calculating Implied Probability
Odds imply how likely the sportsbook thinks an outcome is:
Odds and Implied Probability
| American | Implied Probability | True Meaning |
|---|---|---|
| -300 | 75% | Very likely to happen |
| -150 | 60% | More likely than not |
| +100 | 50% | Even odds |
| +200 | 33% | Underdog |
| +500 | 16.7% | Long shot |
The Vig Hidden in Odds
Sportsbooks don't offer fair odds. The implied probabilities on both sides add up to more than 100%:
The extra 4.8% is the sportsbook's guaranteed profit margin.
Strategy Insight
Key Takeaways
- 1American odds: + shows profit on $100, - shows stake needed to win $100
- 2Decimal odds: multiply by stake for total return
- 3Fractional odds: numerator/denominator shows profit ratio
- 4Implied probability reveals how likely books think outcomes are
- 5Both sides' probabilities exceed 100%—the difference is vig