Remove the bookmaker vig from two-way odds to reveal fair probabilities and zero-margin prices.
A bookmaker builds its edge into both sides of a market, so the two implied probabilities add to more than 100%. Removing the vig means scaling them back to 100% to reveal the fair price behind the quote — the number the book itself is working from.
That fair price is the benchmark for everything else. If another book offers better than the fair price on the same outcome, you have found value; if your own estimate beats it, you have found an edge.
The simple approach divides each implied probability by their sum. It assumes the margin is applied proportionally, which is close enough on balanced two-way markets and less accurate on heavy favourites, where books usually load more margin onto the long shot.
For that reason treat a no-vig line on a 1.05 favourite with more caution than one on an even market.
Stripping the margin gives you the book’s own estimate of the probability, which is the benchmark for everything else. Comparing that estimate against another book’s price is how a stale line becomes visible.
It is also the honest input to an expected-value calculation. Feeding raw priced odds into an EV formula measures the margin, not your edge; feeding de-vigged probabilities measures the disagreement between you and the market, which is the thing that could actually be profitable.
They should — the offered odds are worse than fair by exactly the margin. No-vig shows you what the bet would pay in a market with no house edge.
Not at a bookmaker. Exchanges and prediction markets come closest, since they charge commission rather than build a spread.