Every posted line has the book's margin baked in. Remove it to see the market's true probability.
Convert each side's odds to an implied probability (for decimal odds d, that's 1/d). Because of the bookmaker margin, the probabilities sum to more than 100% — the excess is the overround. Dividing each implied probability by the total rescales them to a fair 100%:
fair pi = (1/di) ÷ Σ(1/dj)
A spread at −110 / −110: each side implies 52.38%, totalling 104.76% — a 4.76% overround (the book keeps ~4.55% of matched handle). De-vigged, each side is exactly 50%, so the fair price is +100 (decimal 2.00). That's why beating −110 requires winning 52.38% of the time, not 50%.
A soccer match at 2.10 / 3.30 / 3.80 implies 47.62% + 30.30% + 26.32% = 104.24%. De-vigged: 45.7% / 29.1% / 25.2% — fair decimals of about 2.19 / 3.44 / 3.96.
This proportional method is the standard first-pass de-vig. EdgeFinder applies it across every book and market to anchor its fair prices.
Deep dive: De-vigging explained →
The bookmaker's built-in margin. Implied probabilities of all outcomes sum to more than 100%; the excess is the book's expected cut regardless of the result.
They are the market's true probability estimate. A bet is only +EV when the price you take beats the fair (no-vig) probability — comparing to the posted price of one book tells you nothing.
No — power and Shin methods model favorite–longshot bias more precisely. Proportional is the standard baseline and is what this calculator uses.
Expected value of a bet from your fair win probability and the offered price.
Check two or three prices for a guaranteed profit and split your stake exactly.
Optimal bet size from your edge and bankroll, with half- and quarter-Kelly presets.