Free Tool
Implied Probability & Overround
Enter the decimal odds for every runner in a race (or both sides of a match) to see the bookmaker's overround and each runner's fair, margin-free odds.
Total implied probability: 108.3%
Bookmaker overround (margin): 8.3%
How to use this calculator
- Enter the decimal odds for every runner in the race (or both sides of a match).
- Add more runners with the button below the list if you need more than 3.
- Check the total at the bottom - anything over 100% is the bookmaker's built-in margin.
What implied probability actually means
Implied probability is simply 1 ÷ decimal odds, expressed as a percentage - it's what the odds say the true chance of that outcome is, according to the bookmaker's pricing.
What overround (the margin) is
If you add up the implied probability of every possible outcome in a race, a genuinely fair market would total exactly 100%. Bookmakers price every runner slightly shorter than its true chance so the total comes to more than 100% - that excess is the overround, and it's built into every price you see. The "fair odds" this tool shows strip that margin back out, so you can see what each runner's price would be in a zero-margin market.