Sportsbook odds include the vig, the book's built-in margin, so the implied probabilities of both sides add up to more than 100%. Devigging strips that margin out to reveal the fair probability the market is actually pricing.
Enter both sides of a line below. The calculator shows each side's fair, no-vig probability and the total vig, then lets you drop in a Kalshi price to see whether the contract is cheap or rich against the fair line.
Enter both sides of a sportsbook line. The vig gets stripped to give the fair probability you can compare against a Kalshi price.
FAIR PROB · SIDE A
58.0%
raw 60.0%
FAIR PROB · SIDE B
42.0%
raw 43.5%
VIG (OVERROUND)
3.5%
Compare to a Kalshi contract for Side A:
Fair value is 58.0¢. At 58¢ on Kalshi you are right at fair value.
Devigging assumes the book’s margin sits proportionally across both sides (the multiplicative method). It is a clean estimate, not gospel, sharper books and lopsided markets distribute vig unevenly.
Why the vig matters
If one side is -150 and the other +130, their raw implied probabilities sum to more than 100%. That extra is the vig. Comparing a raw sportsbook number directly to a Kalshi price overstates the true probability, because Kalshi contracts settle at $1 with no two-sided margin baked in the same way.
Devigging normalizes both sides back to 100% so you are comparing apples to apples. A Kalshi contract trading below the no-vig fair value is the kind of edge sharp traders hunt for.
How the math works
Convert each side's odds to a raw implied probability, add them to get the overround, then divide each side by that total. The result is the fair probability with the margin removed. This is the multiplicative devig method, the most common approach.
FAQ
What does devigging mean?
Removing the bookmaker's margin (the vig) from a two-sided line so the two probabilities sum to 100%, leaving the fair probability the market implies.
How do I compare a sportsbook line to Kalshi?
Devig the sportsbook line to get the fair probability, convert it to cents, and compare it to the Kalshi contract price. A contract below fair value is cheap; above it is rich.
Is the no-vig price exact?
It is a clean estimate using the multiplicative method, which spreads the margin proportionally across both sides. Real books sometimes load more vig on one side, so treat it as a strong approximation.
Stop calculating one trade at a time
ContractTax does this across your whole Kalshi history: real P&L, a Sharp Score that rates your edge, and your tax numbers under every treatment.
These tools are for education and estimation only, not financial or tax advice. Fee estimates use Kalshi’s standard formula and may differ from your actual fees.