No-Vig Odds: How to Remove the Sportsbook’s Margin
What the vig is, two ways to strip it out of a price, and why the method you pick can flip a bet from +EV to −EV.
The Smart Lines teamOctober 20265 min read
What the vig is
The vig (short for vigorish, also called juice or margin) is the sportsbook’s built-in cut. Books price both sides of a bet so that their implied probabilities add up to more than 100%. The extra is how the book makes money regardless of the result.
The classic example is a game priced −110 on both sides. Each side implies a 52.38% chance of winning, so the two add up to 104.76%. A true coin flip is 50/50, so the book has priced in a 4.76% overround (it keeps about 4.5% of all money bet if action is balanced).
What no-vig odds are
No-vig odds (also called fair odds) are what the prices would be with the margin taken out, so the probabilities add up to exactly 100%. They’re the market’s honest estimate of each side’s chances, and they’re the benchmark for finding +EV bets: if another book pays more than the fair price, that bet has positive expected value.
Method 1: proportional (the simple one)
Convert each price to an implied probability, then scale them so they sum to 100%:
fair probability = implied probability ÷ (sum of all implied probabilities)
Example
Favourite −150, underdog +130
- Favourite −150: implied 150 ÷ 250
- 60.00%
- Underdog +130: implied 100 ÷ 230
- 43.48%
- Total (3.48% overround)
- 103.48%
- Fair favourite: 60.00 ÷ 103.48
- 57.98% (−138)
- Fair underdog: 43.48 ÷ 103.48
- 42.02% (+138)
This is what our no-vig calculator does. It’s quick, easy to check by hand, and good enough for most two-way markets with a small margin.
Method 2: the power method (better for underdogs)
Bettors tend to overpay for longshots, and books know it, so they usually put more of their margin on the underdog than on the favourite. This is called the favourite-longshot bias. The proportional method spreads the margin evenly, so it can make underdogs look slightly more likely than they really are.
The power method instead finds one exponent k so that each implied probability raised to the power k sums to exactly 1. It takes a little more margin off the longshot. For the same game:
- Fair favourite (power method)
- 58.40% (−140)
- Fair underdog (power method)
- 41.60% (+140)
The Smart Lines’ +EV scanner uses the power method to remove each book’s margin before it compares prices.
Why it matters
Another book offers the underdog at +140
- EV against the proportional fair price (42.02%)
- +0.8%
- EV against the power-method fair price (41.60%)
- −0.2%
Same bet, same prices. One method calls it a small +EV bet and the other calls it slightly −EV. Small edges live or die on details like this, so treat any edge under about 1% with suspicion.
Which book’s prices should you de-vig?
Fair odds are only as good as the prices they come from. Removing the margin from a slow or heavily shaded book just gives you that book’s opinion without the margin. The usual choices are:
- A sharp book. Pinnacle takes large bets from professionals and moves its lines quickly, so its prices are widely used as the reference.
- A consensus. The median fair price across several independent books smooths out any one book’s mistakes. Books that copy each other’s prices should only count once.
The short version
- The vig is the amount the implied probabilities add up to over 100%.
- No-vig odds remove it to give the market’s fair estimate of each side.
- The proportional method is simple; the power method is more accurate for underdogs.
- De-vig a sharp book or a consensus, using matching lines and fresh prices.
Try it with the no-vig calculator, or turn fair odds into percentages with the implied odds calculator.