How to calculate implied probability
Implied probability = 1 ÷ decimal odds
- Decimal odds: 1 ÷ odds. At 2.50 that's 40%.
- American odds: for +150, 100 ÷ (150 + 100) = 40%; for −110, 110 ÷ (110 + 100) = 52.38%.
- Fractional odds: for 3/2, 2 ÷ (3 + 2) = 40%.
Why the probabilities add up to more than 100%
A bookmaker's prices include its margin, so the implied probabilities of every outcome add up to more than 100%. At −110 on both sides the total is 104.76%. The fair probability removes that excess: we use the power method, the same one as the no-vig calculator.
Examples
| Odds | Implied probability |
|---|---|
| 1.50 (−200, 1/2) | 66.67% |
| 2.00 (+100, 1/1) | 50.00% |
| 2.50 (+150, 3/2) | 40.00% |
| 4.00 (+300, 3/1) | 25.00% |
The full explanation, with a longer table, is in the guide to implied probability in betting.
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