Convert every price in a market to an implied probability (one divided by the decimal odds) and add them up. A fair market would sum to exactly 100%. Real markets sum higher — 1X2 football at recreational books typically lands between 104% and 107%. That surplus is the margin, also called the vig or overround: the bookmaker's cut, baked into the prices.
The margin means you can pick winners and still lose money. If you pay 5% over the true price on every bet, you need to be more than 5% better than the market just to break even — a bar almost nobody clears.
Devigging is the arithmetic that strips the margin back out. The simplest method divides each implied probability by the market total; better methods recognise that books load more margin onto longshots than favourites and adjust proportionally. What is left is the book's own opinion of the true probabilities, cleaned of its fee.
We devig the sharpest market in the world for every match on the site, then compare soft bookmakers' prices against those margin-free probabilities. When a soft book quotes above the fair price, that is a value flag. When none does — which is most of the time — we say so plainly.
See how we apply this on every match in our methodology. Methodology →
See these ideas at work in our public track record — every call logged before kick-off, losses included.