Published by ParlayAPI. A free tool. The math runs entirely in your browser; none of the odds you type ever leave this page.

No-Vig Devig Calculator

Paste in the two (or three) prices a book is offering. This strips out the bookmaker margin and gives you the fair win probability and fair odds for each side, plus the hold. Type any price and it recomputes instantly.

Odds format
Market
Method
Hold / vig   --
Overround   --
Outcome Your price Implied Fair prob Fair decimal Fair American

Built on the same math ParlayAPI runs. This is the exact devig used by ParlayAPI's /v1/devig and /v1/ev endpoints, applied at scale across 45+ sources instead of one line at a time. Get it via the API.

How it works

A bookmaker's prices always add up to more than 100% implied probability. That extra slice is the vig (also called the margin, juice, or hold). Devigging removes it so you can see what the book actually thinks each outcome's chance is.

  1. Convert each price to an implied probability: p = 1 / decimal odds.
  2. Add the implied probabilities. The total is the overround, and it is greater than 1.
  3. Divide each implied probability by the overround. Now they sum to exactly 1. Those are the fair probabilities.
  4. Convert back: fair decimal = 1 / fair probability, and to American if you prefer.
# 2-way p1 = 1 / dec1 , p2 = 1 / dec2 overround = p1 + p2 ( > 1 ) hold = overround - 1 fair1 = p1 / overround , fair2 = p2 / overround fair decimal = 1 / fair # 3-way is the same with three prices summed overround = p1 + p2 + p3

This is the proportional method (each probability is scaled by the same factor, 1 / overround, which is why it is also called the multiplicative method). It is the standard, transparent default. Other approaches exist for splitting the margin unevenly between favorite and longshot (additive, Shin, power) and can be a better fit for heavy favorites, but they need extra assumptions; proportional makes none.

American and decimal conversions used here

American to decimal: if odds > 0: dec = 1 + odds/100 if odds < 0: dec = 1 + 100/|odds| Decimal to American: if dec >= 2: american = (dec - 1) * 100 if dec < 2: american = -100 / (dec - 1) Implied probability: p = 1 / dec

What this does not do

Removing the vig tells you the market's fair price, not the true probability of the event. A single book can be wrong or slow. For a sharper estimate, devig a sharp market (or a consensus of several books) rather than the same book you are betting into, and compare that fair price against the price you can actually get. That comparison is exactly what an expected-value check does.