Implied probability calculator
Odds are just probabilities in disguise. This converter translates in both directions, and accepts decimal (2.50), fractional (3/2) and American (+150 or -120) formats — it returns the American equivalent alongside the probability.
The formula
Implied probability = 1 ÷ decimal odds. Odds of 2.50 imply 40%. Going the other way, fair decimal odds = 1 ÷ probability, so a 40% chance is fair at 2.50.
Why the probabilities never add up to 100%
Add the implied probabilities across every outcome of a market at one bookmaker and you will get more than 100% — usually 102–110%. The excess is the overround, the bookmaker's built-in margin. Arbitrage exists when combining the best odds from different bookmakers pushes the combined implied probability below 100%. Check any combination with the arbitrage calculator.
Where this matters in practice
- Comparing books: lower combined implied probability means a sharper price for you.
- Value betting: if your estimated probability beats the implied probability, the bet is positive EV — quantify it with the EV calculator.
- Reading software output: scanners like the tools in our comparison hub express edges as percentages built on exactly this conversion.
More calculators: see the full set.