De-Vigging, in plain words
De-vigging, also written devig or no-vig, removes the sportsbook's margin from a market so the sides add up to exactly 100%. What is left is the market's own estimate of each side's chance, which is the fair line every edge is measured against.
The simplest method is proportional: divide each side's implied probability by the total. Other methods, such as additive and power, share the margin out differently, because books tend to load more of their margin onto the longshot. On a near-even market the methods agree to a fraction of a percent. On a lopsided one they can disagree by more, and the choice matters.
A fair line is only as good as the market it comes from. De-vigging one soft book's prices tells you what that book thinks. De-vigging a sharp book, or a consensus of several, tells you what the market thinks, and that is the number a +EV board compares every other price against.
The idea, drawn
Worked example · illustration
A market at −135 / +115
- Side A
- −135 (57.45%)
- Side B
- +115 (46.51%)
- Fair A
- 55.26%
- Fair B
- 44.74%
- Implied: 57.45% + 46.51% = 103.96%.
- Proportional: 57.45% / 103.96% = 55.26%, and 46.51% / 103.96% = 44.74%.
- As prices, the fair line is −124 / +124.
Any book offering side B above +124 is paying more than this market thinks it is worth.