How to devig odds

How do you find the true probability behind a sportsbook's price?

A sportsbook's prices imply probabilities that add to more than 100%. The surplus is the margin. Devigging redistributes it to recover what the book actually believes — and how you redistribute it is a modelling choice, not arithmetic.

On a -145 / +125 moneyline, the four standard methods give the favourite anywhere from 57.11% to 57.50%:

additive — 57.37%

multiplicative — 57.11%

power — 57.50%

shin — 57.37%

That spread is 0.39 points of probability on a market where a 2% edge is a good day. Multiplicative is the usual default because it is one division, but it distributes the margin in proportion to implied probability — the opposite of the favourite-longshot bias real markets show, which makes it the method most likely to overstate a longshot.

The practical answer: do not pick one. An edge that exists under one method and vanishes under another is a modelling artefact. Work it through →