Sports betting odds explained.
How decimal, fractional and American formats express the same underlying price—and how to calculate return and implied probability.
Odds describe a potential payout and imply a probability. They do not tell you what will happen.
Decimal odds
Decimal odds show the total return per unit staked, including the stake. At 2.50, a stake of 10 returns 25 if the bet wins: 15 profit plus the 10 stake.
Fractional odds
Fractional odds show potential profit relative to stake. Odds of 3/2 mean 3 profit for every 2 staked. Add the stake back to find total return.
American odds
Positive odds show profit on a 100 stake: +150 means 150 profit on 100. Negative odds show the stake needed for 100 profit: −200 means 200 staked for 100 profit.
| Decimal | Fractional | American | Implied probability |
|---|---|---|---|
| 2.00 | 1/1 | +100 | 50% |
| 2.50 | 3/2 | +150 | 40% |
| 1.50 | 1/2 | −200 | 66.67% |
Implied probability
For decimal odds, divide 1 by the odds and multiply by 100. At 2.50, 1 ÷ 2.50 = 0.40, or 40%.
Why market probabilities add above 100%
The combined implied probabilities often include the bookmaker’s margin. Comparing prices may reduce the margin you accept, but it cannot guarantee profit.
Common mistakes
- Confusing total return with profit.
- Reading −200 as a larger potential profit than +200.
- Treating implied probability as an objective forecast.
- Ignoring settlement rules, voids and market-specific terms.
One rule above every tactic
Only gamble with money you can afford to lose. Set limits before you start, never chase losses, and stop if play no longer feels optional.
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