What is de-vigging?
How to remove the sportsbook's built-in margin from a line so you can compare the market's true probability estimate against your own.
De-vigging (or “no-vig”) means removing the sportsbook's built-in profit margin — the vig — from a betting line to reveal the market's true implied probability. Because both sides of a market add up to more than 100%, you normalize them back to 100% by dividing each side's raw implied probability by the total. The result is the fair price the market actually believes, which is the honest benchmark you compare your model against.
Every posted price is inflated by the vig, so the raw implied probabilities of both outcomes sum to something like 104–110% instead of 100%. If you compare your model to the raw number you will think you have edge that is really just the book's margin. De-vigging removes that illusion so you measure your model against the market's genuine opinion.
Say a game is priced −110 / −110. Each side's raw implied probability is 110/210 = 52.38%, summing to 104.76%. Divide each by 104.76% and you get 50% / 50% — the no-vig fair line. Do the same with real numbers like −150 / +130: raw probabilities 60.0% and 43.5% sum to 103.5%, so the de-vigged favorite is 60.0/103.5 = 57.97%.
De-vigging is the backbone of how we measure ourselves honestly. We compute closing line value as no-vig opening price versus no-vig closing price, which is why our reported CLV (+0.39pp over 193 measured picks) is a clean, margin-free number rather than a flattering one.
What does de-vig mean?De-vigging means removing the sportsbook's margin from a line to find the true implied probability. You convert each side to implied probability, add them (they exceed 100%), then divide each by the total so they sum to 100%.
Why do the two sides add up to more than 100%?The extra amount is the vig — the book's built-in commission. It is how sportsbooks profit regardless of outcome, and it is exactly what de-vigging strips out to reveal the fair price.
How does Signal Labs use de-vigging?We de-vig both the opening and closing prices to measure closing line value cleanly. Comparing no-vig open to no-vig close removes the book's margin so our CLV reflects genuine market movement, not commission.