Vig Calculator and No-Vig Fair Value
Find the margin baked into any two-sided market, and what the prices would be without it.
What it costs to buy the outcome happening.
What the opposite side costs on the same venue.
A 2.9% hold is normal for a liquid prediction market — far below the 4–5% a sportsbook typically builds into a two-way line.
How it works
Quote both sides of a market and the implied probabilities should sum to exactly 100%. They never do. The excess is the overround, and the share of every dollar it represents is the vig — the margin the venue or the market itself takes for making the price.
Prediction markets carry far less of it than sportsbooks. A two-way sportsbook line typically holds 4–5%; a liquid market on Kalshi or Polymarket often sits under 1%, because you are trading against other users rather than a house that needs a margin. That is the structural argument for the category, and it is covered in full in prediction markets vs sports betting.
Stripping the vig gives you the market's actual opinion. That no-vig number is the thing worth comparing against your own estimate, or against the same market on another venue — which is what our live arbitrage scanner does automatically across Polymarket and Kalshi.
Frequently asked questions
What is vig in a prediction market?
The margin built into the prices. If YES and NO together imply more than 100%, the excess is the overround, and the vig is that excess as a share of the total — what transacting costs you before any explicit fee.
How do you remove the vig from odds?
Divide each implied probability by their total. YES at 54% and NO at 49% sum to 103%, so fair value is 52.4% and 47.6%. That is the multiplicative method — standard, though it flatters the favourite slightly on lopsided markets.
What is a normal vig on Polymarket or Kalshi?
Under 1% on liquid markets, often a fraction of that on the deepest books. Wide numbers on thin markets usually mean nobody is quoting, not that the venue is charging you.
Other calculators
For live prices instead of hypotheticals, see the Polymarket vs Kalshi arbitrage scanner, or compare the venues in our head-to-head breakdown.
