How to devig sportsbook odds
Devigging (removing the vig, or juice) converts a sportsbook's priced odds into an estimate of the true underlying probability. It is the single most important calculation in any +EV workflow. There are three standard methods — they often disagree, which matters.
Why the vig exists
A fair coin flip is +100 on both sides (50% / 50%, no margin). A sportsbook offering both sides at +100 would make zero money. So they price each side at -110: implied probability 52.4% per side, summing to 104.8%. That extra 4.8% is the vig. To estimate true probability, you have to remove it.
Method 1: Multiplicative devig
Divide each side's implied probability by the sum of all sides' implied probabilities. If both sides are 52.4%: 52.4 / 104.8 = 50.0% each. Simple, fast, and assumes the vig is distributed proportionally.
Multiplicative is the default in most retail tools because it is easy to compute and works well on balanced markets.
Method 2: Additive devig
Subtract half of the overround from each side's implied probability. If both sides are 52.4%, overround is 4.8%, so subtract 2.4% from each: 50.0% each. On a balanced market, additive gives the same answer as multiplicative.
Additive diverges from multiplicative on unbalanced markets (e.g., heavy favorites). Some practitioners prefer additive for spread/total markets.
Method 3: Power devig
Raise each implied probability to a power k chosen so that the powered probabilities sum to 1.0. This adjusts the vig non-linearly, taking more vig from the favorite and less from the underdog. Many sharps consider power devig the most theoretically correct for heavily skewed markets.
Why the three methods matter together
On balanced markets the three methods agree to within fractions of a percentage point. On heavy favorites (-300, -500) they can disagree by 1-2 percentage points, which is enough to flip an apparent +EV bet into -EV.
Worst-case devig runs all three methods and returns the most conservative fair price. If a bet shows positive edge against the worst-case price, it has positive edge against every common devig method.
Frequently asked
Which devig method is "correct"?
There is no single correct method — each makes a different assumption about how the book distributes its margin. On most markets the difference is small. On heavy favorites the difference can matter, which is why conservative bettors use worst-case (the most cautious of the three).
Should I devig two-way or three-way?
Devig must match the actual market structure. A soccer 1X2 market has three outcomes and must be devigged three-way; treating it as two-way produces wrong fair prices. EvqBet auto-detects market shape per sport and devigs accordingly.