How do I calculate a no-vig price?
Short answer: Convert each side's American odds to an implied probability, add the two, and divide each side by that total. For example, -110 on both sides implies 52.38% each, 104.76% together, so each side's no-vig probability is 50%.
The formula
- Implied probability of each side. Negative odds: price ÷ (price + 100), so -140 is 140 ÷ 240 = 58.3%. Positive odds: 100 ÷ (price + 100), so +120 is 100 ÷ 220 = 45.5%.
- Add the two sides. 58.3% + 45.5% = 103.8%. The 3.8 points over 100% is the book's margin, the vig.
- Divide each side by the total. Under 58.3 ÷ 103.8 = 56.2%, over 45.5 ÷ 103.8 = 43.8%. They now add to 100%.
Worked example: a points prop
Points 24.5, Over -105 / Under -125. Over implies 105 ÷ 205 = 51.2%; under implies 125 ÷ 225 = 55.6%; total 106.8%. No-vig: over 51.2 ÷ 106.8 = 47.9%, under 55.6 ÷ 106.8 = 52.1%.
Turning a no-vig probability back into a fair price
Above 50%: fair price = -(p ÷ (1 − p)) × 100, so 52.1% is about -109. Below 50%: fair price = ((1 − p) ÷ p) × 100, so 47.9% is about +109.
Which method?
This is the proportional (multiplicative) method. Power and Shin methods push a little more of the margin onto the longer price. On near-even player props they usually agree within a fraction of a point, so the simple method is fine for comparing books.
The full guide, with why it matters, is Removing the vig. The props page shows both books' prices for every line posted tonight.
Common mistakes
- Mixing lines. A no-vig probability belongs to one line. Over 24.5 at one book and under 25.5 at another are different bets, and combining them gives a meaningless number.
- Mixing times. Prices move through the day. Take both sides of a market from the same moment, or the "margin" you compute includes a price change.
- Using one side only. A single price tells you the implied probability including the vig. You need both sides to remove it.
- Rounding too early. Keep a decimal place through the division; on near-even props, rounding can move the answer by half a point.
Why bother?
A no-vig probability lets you compare two books fairly, judge whether a price is generous, and estimate the margin you pay. It is the basic unit behind every comparison on OpenSlate, and the first number to check before believing any claim that a bet has value. It also shows how much a book is charging you on that market, because the gap between the raw and no-vig probabilities is exactly the vig.
Related questions
- What is a +EV player prop?: what positive expected value means and why automated screens can mislead.
- Why do DraftKings and Pinnacle lines differ?: the business, timing and news reasons two books disagree on the same line.
- What is a Trap Over?: why a cheap-looking Over is listed apart instead of treated as value.
- How do I compare prop odds for free?: a step-by-step method and the free page that does it.
Every answer on these pages is market data and education. OpenSlate does not publish free picks and does not tell you what to bet; it shows prices and measurements.
More: Removing the vig: how to turn two prices into a fair probability · 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? · 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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