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No-vig fair odds calculator

Enter every side of a market in American, decimal or Polymarket cents. The calculator strips the margin and shows the fair price for each side.

No-vig calculator illustration

What the vig is

A sportsbook prices both sides so the implied probabilities add up to more than 100%. The extra is the vig, also called juice or overround. At −110 on both sides each side implies 52.4%, the total is 104.8%, and the book’s margin is 4.8%.

implied q = 1 ÷ d for each side; fair p = q ÷ (sum of all q)

Removing the vig rescales the probabilities so they add up to 100%. What is left is the book’s fair estimate of each side.

Two ways to remove it

  • Multiplicative (proportional): divide each implied probability by the total. Simple and the most common method.
  • Power: raise each implied probability to the power k that makes them sum to 1. It takes more margin off the longshot, which matches how books shade favorite–longshot lines.

Arbs’s own model uses the power method on two-way lines before it blends books into a consensus price. The no-vig guide walks through both, and Shin’s method for three-way markets.

Worked example

Worked example: Favorite −150, underdog +130

  1. Implied: 60.0% + 43.5% = 103.5%, a 3.5% overround
  2. Fair (multiplicative): 60.0 ÷ 103.5 = 58.0% and 43.5 ÷ 103.5 = 42.0%
  3. Fair (power): 58.4% and 41.6%

The fair line is about −138 / +138 by the multiplicative method.

If Polymarket sells the underdog at 38¢, you pay 38% for a side the book’s fair line puts at 42%. That is the kind of gap Arbs flags on the live board.

Frequently asked questions

How do you calculate no-vig odds?

Convert every side to an implied probability, add them up, then divide each one by the total. The results add to 100% and are the fair probabilities. Convert them back to odds for the fair line.

What is a normal vig?

About 4.5% on a −110/−110 spread or total. Moneylines on big favorites and player props often carry 6–10%. Polymarket has no built-in vig, but taker orders pay a fee.

Which devig method is best?

For a balanced two-way line they agree. On lopsided lines and three-way soccer markets the power method usually fits better because books load more margin onto longshots.

Why compare no-vig odds to Polymarket?

A sharp book’s no-vig price is a strong estimate of the true probability. When Polymarket sells a side for less than that, the share is underpriced.

Read the guide: What are no-vig fair odds and how to calculate them

See today’s model gaps on the live board · How Arbs prices games

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