Quick answer
Overround: The overround is the amount by which a bookmaker market's implied probabilities exceed 100%; it is the bookmaker's built-in margin, also called the vig or juice.
Also called: vigorish, bookmaker margin, juice
Explained, with an example
Example: a two-way market at 1.90 / 1.90 has implied probabilities of 52.63% each, a book sum of 105.26% and an overround of 5.26%; removing it gives fair odds of 2.00 / 2.00 [1]. The simplest no-vig method divides each implied probability by the book sum (proportional normalisation); other methods exist, and they can give slightly different fair prices for long shots. Sharper books usually run lower margins (Sharp vs soft bookmakers).
Formula
booksum = Σ 1 / oddsᵢ
overround = booksum − 1
fair (no-vig) probability pᵢ = (1 / oddsᵢ) / booksum
fair odds = 1 / pᵢTry it: tools and tutorials
Frequently asked questions
What is overround?
The overround is the amount by which a bookmaker market's implied probabilities exceed 100%; it is the bookmaker's built-in margin, also called the vig or juice.
About this guide
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Author: Ken Lin · Corrections: if you spot an error, we review it and date-stamp the fix.
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Sources
- Bookmaker Margin Calculator (overround, fair odds) — Odds-API.io tools, accessed 2 Nov 2026