Removing the vig: how to turn two prices into a fair probability
Every two-way price at a sportsbook carries a margin. If you add up the probabilities that the over and the under imply, you get more than 100%. The extra is the book's edge, usually called the vig or juice. Removing it gives you the "no-vig" or "fair" probability: what the book's prices say about the outcome once its cut is taken out.
Step 1: turn American odds into implied probability
For a negative price, divide the price by itself plus 100: -150 implies 150 ÷ 250 = 60.0%. For a positive price, divide 100 by the price plus 100: +130 implies 100 ÷ 230 = 43.5%.
Step 2: add the two sides
Take a rebounds prop at 5.5 priced Over +115 / Under -140. The over implies 100 ÷ 215 = 46.5%. The under implies 140 ÷ 240 = 58.3%. Together that is 104.8%. The 4.8 points above 100% is the margin on this line.
Step 3: scale back to 100%
Divide each side by the total. Over: 46.5 ÷ 104.8 = 44.4%. Under: 58.3 ÷ 104.8 = 55.6%. Those two now add to 100%, and they are the book's fair view of the line.
This is the simplest method, often called proportional or multiplicative de-vigging. Other methods (power, Shin) move a little more of the margin onto the longer price; on near-even player props the methods usually agree within a fraction of a point.
Why compare no-vig numbers instead of prices?
Two books can show the same line with different margins. DraftKings might price a line -120 / -110 while Pinnacle prices it +115 / -140. Comparing -120 with -140 directly mixes the margin into the comparison. Comparing no-vig probabilities removes it: you are comparing what each book actually believes about the outcome.
That is exactly what the OpenSlate gap board does. For every line both books quote, it computes the no-vig probability at DraftKings and at Pinnacle on the identical line, and shows the difference in percentage points. A gap of +3.0pp on the under means Pinnacle's prices rate the under three points likelier than DraftKings' prices do.
What a gap does and doesn't tell you
- It is a disagreement, not a forecast. Pinnacle is the market's reference price (see why), but it is not always right, and a single game is noise.
- Large gaps are often news. A gap of 5 or more points usually means one book has priced an injury or rest report the other hasn't. The board flags these as CHECK NEWS rather than publishing them.
- Gaps close. Books move toward each other, often within the hour. That is what MOVED means on the board; see why lines move.
- The price you get matters. A no-vig number is only useful against the price that is actually available. A gap measured an hour ago may already be gone.
One last practical point: always compare like with like. A no-vig number from a line at 5.5 rebounds says nothing about a line at 6.5, and a price read this morning may not be the price available now.
Quick reference
| Price | Implied |
|---|---|
| -200 | 66.7% |
| -150 | 60.0% |
| -120 | 54.5% |
| -110 | 52.4% |
| +100 | 50.0% |
| +120 | 45.5% |
| +150 | 40.0% |
| +200 | 33.3% |
More: Why Pinnacle is the reference price · Closing line value, explained · Why parlays cost more than the same bets straight · Why player prop lines move · Is DraftKings or Pinnacle sharper on NBA player props? · How do I calculate a no-vig price? · What is a +EV player prop? · Why do DraftKings and Pinnacle prop lines differ? · What is a Trap Over? · Are NBA rebound unders profitable? · How do I compare sportsbook prop odds for free? · What does closing line value tell me? · How often do prop lines move before tip-off? · What is the vig on DraftKings player props? · How do injury reports move NBA prop lines? · What is a market-maker sportsbook? · Is it better to bet the over or the under on player props? · Can you make money betting player props? · Can you bet at Pinnacle from the US? · What free tools help with player prop betting? · Does betting DraftKings when it disagrees with Pinnacle work? · What does over/under mean on a player prop? · How do sportsbooks set player prop lines? · What is a sharp bettor? · How do I convert American odds to implied probability? · What is a steam move in sports betting? · What are alternate lines on player props?
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