Overround Calculator
Calculate market percentage, bookmaker margin, and no-vig fair odds from any 2-way, 3-way, or multi-runner market. Useful for comparing books, pricing your own tissue, and spotting where the margin is too heavy.
Overround Calculator
Enter all available outcomes to reveal the total book percentage and fair prices
What overround means
Bookmaker margin in one number
Overround is the amount by which the implied probabilities in a market add up to more than 100%. That excess is the bookmaker's built-in margin, sometimes called the hold or vig.
The formula
Overround = (1 / odds1 + 1 / odds2 + 1 / odds3 + ...) - 1
Convert that total to a percentage and you get the market percentage. A 103.50% book means the margin is 3.50%.
Above 100%
The market has bookmaker edge built in. The further above 100%, the harder it is to beat without strong pricing or line shopping.
Below 100%
The market is underround. That is unusual at a single book and more common when combining best prices from multiple sportsbooks.
Common overround examples
| Market | Example Prices | Book % | Margin | Read |
|---|---|---|---|---|
| 2-way tennis | 1.91 / 1.91 | 104.71% | 4.71% | Typical sharp-ish margin |
| 3-way football | 2.10 / 3.40 / 3.60 | 105.85% | 5.85% | Standard soft-book margin |
| Outright market | Multiple runners | 120%+ | 20%+ | Often much tougher to beat |
| Best-price combined | 2.10 / 2.10 | 95.24% | -4.76% | Potential arbitrage / underround |
How to use it well
- •Strip the vig first: If you want fair win probabilities, normalize the market back to 100% before comparing it to your model.
- •Compare books by margin: Two books may show similar headline prices but very different overall market percentages.
- •Watch outrights carefully: Multi-runner markets can hide heavy margin because the overround is spread across many selections.
- •Use with EV and Kelly: Fair odds help you judge whether your edge is real before deciding stake size.
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