What Are Betting Odds?
Every time you open a betting site, you see numbers next to each team or player. Those numbers are the odds. They are set by the bookmaker's trading team based on statistical models, historical data and market activity. The higher the odds, the less likely the bookmaker thinks that outcome is, and the more you stand to win if it happens.
Odds also contain a built-in margin for the bookmaker, known as the vig or overround. This is how betting sites make money regardless of the result. Understanding this margin helps you identify which bookmakers consistently offer better value. You can compare the top licensed bookmakers on our Betting Sites page.
Decimal Odds - The Global Standard
Decimal odds are the most widely used format internationally and the default on most European, Australian and Canadian betting sites. They show your total return per unit staked, including your original stake.
Real Madrid to win at 2.50 decimal
You bet $10. Total return = $10 × 2.50 = $25 ($15 profit + $10 stake back)
Barcelona at 1.40 decimal
You bet $10. Total return = $10 × 1.40 = $14 ($4 profit + $10 stake back)
Quick rule: Decimal odds above 2.00 mean you profit more than your stake. Below 2.00 means you profit less than your stake. Exactly 2.00 means you double your money.
Fractional Odds - The UK & Ireland Format
Fractional odds are traditional in the United Kingdom and Ireland and remain the default on many British betting sites, particularly for horse racing. They show profit relative to your stake, your original stake is not included in the fraction.
Real Madrid at 3/1 fractional
You bet $10. Profit = $10 × 3 = $30. Total return = $40 (profit + stake back)
Barcelona at 2/5 fractional
You bet $10. Profit = $10 × (2/5) = $4. Total return = $14
American Odds - The US Format
American odds are the standard format on US sportsbooks and use a plus (+) or minus (-) sign. Positive odds show how much profit a $100 bet returns. Negative odds show how much you need to stake to win $100.
Real Madrid at +200 (underdog)
Bet $100 → profit $200. Total return = $300
Barcelona at -180 (favourite)
Bet $180 → profit $100. Total return = $280
All Three Formats - Side by Side
The same bet expressed in all three formats. The payout is always identical, only the presentation changes.
| Decimal | Fractional | American | $10 stake returns | Implied probability |
|---|---|---|---|---|
| 2.00 | 1/1 (Evens) | +100 | $20.00 | 50% |
| 3.00 | 2/1 | +200 | $30.00 | 33.3% |
| 5.50 | 9/2 | +450 | $55.00 | 18.2% |
| 1.50 | 1/2 | -200 | $15.00 | 66.7% |
| 10.00 | 9/1 | +900 | $100.00 | 10% |
How to Convert Between Formats
What Is Implied Probability?
Every set of odds contains an implied probability, the bookmaker's estimate of how likely that outcome is. You can calculate it from decimal odds using this formula:
Implied probability = 1 ÷ decimal odds × 100
Real Madrid at 2.50: 1 ÷ 2.50 × 100 = 40% implied chance of winning
Barcelona at 1.40: 1 ÷ 1.40 × 100 = 71.4% implied chance of winning
If you believe Real Madrid's true chance of winning is higher than 40%, then 2.50 represents value. This is the foundation of smart betting, identifying when the bookmaker has underestimated a probability.
Which Format Should You Use?
Use the format that is most natural for you and your region. Most modern betting sites allow you to switch formats in settings. Decimal odds are recommended for beginners because the total return calculation is simpler, just multiply your stake by the odds. Bookmakers with a lower margin consistently offer better value. See how the top sites compare on our Best Betting Sites page.