Strip the fee out of a two-sided market and what is left is the book's honest opinion. That number is the yardstick for everything that follows.
Every price you see has a fee inside it. Take the fee out and what is left is the market's actual opinion — the no-vig line, also called the fair line or true price. It is the single most useful number in betting, because every judgement about whether a bet is good is a comparison against it.
For a two-sided market it is three steps, and you can do them in your head with practice.
The market's honest view is 56.2% / 43.8%. Anything better than +128 on the away side is a price above fair.
De-vigging a bad price gives you a fair version of a bad price. The technique does not launder a weak opinion into a strong one.
The convention is to de-vig a sharp book — one that takes large bets and prices tightly — and treat that as the fair number. Its price has been tested by people betting real money into it. A recreational book's number has been tested by nobody, and its de-vigged line is worth much less.
A consensus line built from several books, each de-vigged first, is steadier than any single one. That is what VigWatch prints beside every market on the board.
The division above is the multiplicative method: everyone pays the fee in proportion to their price. It is simple, it is what most tools use, and it has a known flaw — real sportsbooks charge longshots proportionally more than favourites, so on a lopsided market the multiplicative method slightly overprices the longshot.
| Method | How it removes the fee | Weakness |
|---|---|---|
| Multiplicative | Divide each side by the total | Underrates the favourite on lopsided markets |
| Additive | Subtract the excess equally from each side | Can drive a longshot below zero and break |
| Power / Shin | Fit a curve that charges longshots more | More accurate, not something you do in your head |
On a -110 / -110 market all three agree exactly. They only diverge as the market gets lopsided, and by then the honest answer to "what is the fair price?" is: it depends which method you chose. Anyone who presents one number with no method attached is hiding a decision from you.
If you de-vig a book's own price and then compare that book's price against it, you have compared a number with itself. You will find a small negative edge equal to the fee, every time, on every bet. The fair line has to come from somewhere other than the price you are judging.
VigWatch prints a de-vigged consensus line beside every market on the board. See the no-vig consensus.