Devigging

In short: The process of removing the sportsbook’s vig from a set of odds to recover the implied true probability of each outcome. Performed by dividing each outcome’s vig-included implied probability by the sum of all outcome probabilities, producing a normalized set that sums to 100%.

Sportsbook prices don’t reflect true probability directly. They reflect true probability plus the book’s margin. Devigging is the calculation that strips out the margin and leaves you with the book’s actual estimate of what’s likely to happen. It’s the bridge between published odds and the fair-probability reference you need to identify +EV bets.

How devigging works

The standard method is proportional. Take each outcome’s vig-included implied probability and divide by the sum of all outcomes’ probabilities.

A typical moneyline at -110 on both sides:

• Side A at -110 → 52.4% implied probability
• Side B at -110 → 52.4% implied probability
• Combined: 104.8% (the 4.8% excess is the book’s vig)

To devig:

Side A: 52.4% / 104.8% = 50.0%
Side B: 52.4% / 104.8% = 50.0%

The devigged probabilities sum to exactly 100%. In this case, devigging tells you the book thinks the game is a true coin flip.

Now consider an asymmetric market. A team is a meaningful favorite, priced at -175 / +150:

• Favorite at -175 → 63.6% implied probability
• Underdog at +150 → 40.0% implied probability
• Combined: 103.6% (3.6% vig)

Devigged:

Favorite: 63.6% / 103.6% = 61.4%
Underdog: 40.0% / 103.6% = 38.6%

The book’s true-probability estimate is 61.4% on the favorite, 38.6% on the underdog. Those are the numbers to compare against retail offerings when looking for +EV opportunities.

The asymmetric vig problem

Proportional devigging assumes the vig is evenly distributed across outcomes. That’s reasonable for tight markets where both sides are priced near -110, but it gets less accurate as prices get more asymmetric.

Consider a heavy-favorite market priced at -400 / +280:

• Favorite at -400 → 80.0% implied probability
• Underdog at +280 → 26.3% implied probability
• Combined: 106.3% vig

Proportional devigging produces:

Favorite: 80.0% / 106.3% = 75.3%
Underdog: 26.3% / 106.3% = 24.7%

The math works, but there’s a known issue: empirical research shows sportsbooks systematically apply more vig to the longshot side than the favorite side. The actual fair probability of the underdog is typically a couple of points lower than proportional devigging suggests, and the favorite a couple of points higher.

Shin’s adjustment is the most commonly used alternative method that accounts for this longshot bias. It models the vig distribution asymmetrically and produces somewhat different probabilities, particularly on lopsided markets. The math is more involved (it requires solving for a parameter representing the proportion of “insider” bettors) but the result is generally more accurate for heavy favorites and big underdogs.

For most +EV work on tighter markets (-200 to +200 range), proportional devigging is close enough that the difference doesn’t matter much. For longshot bets (+500 and higher), the Shin-adjusted probability is meaningfully different from the proportional one, and proportional devigging will tend to overstate your edge on the underdog side.

Which books are worth devigging

Devigging only produces meaningful results when the underlying prices reflect informed market consensus. Devigging a retail book’s prices gives you a number that’s slightly less wrong than the original, but it’s still the retail book’s view, which is shaped by where the public is betting rather than where the price should be.

The books worth devigging are the ones whose prices reflect sharp action:

• Pinnacle is the standard. Accepts unlimited sharp action, adjusts prices on it, charges 2-3% vig. Pinnacle’s devigged numbers are the closest thing to a true probability reference the market produces.
• Circa Sports posts NFL openers early and welcomes sharps. Devigged prices are reliable, particularly on football.
• Novig is an exchange with no vig built in. Devigging isn’t needed in the traditional sense, but the bid/ask midpoint serves the same purpose as a devigged sharp line.

Devigging averaged prices across many retail books is a common mistake. The retail books shade their lines toward where the public is betting, so the “average retail” line is shaded the same way. Devigging that average just gives you back a vig-removed version of the public consensus, not a true-probability reference.

Where devigging fits in the workflow

Devigging is a method, not a strategy. The full sequence:

1. Pull the current price at a sharp reference book
2. Devig it to get an estimate of true probability
3. Compare to the retail price you’re considering betting
4. If the retail implied probability is meaningfully lower than the devigged sharp estimate, the bet is +EV
5. Calculate the edge size and decide whether it’s worth placing given variance, bankroll, and friction

Devigging is step 2. The rest of the workflow does the actual decision-making. The calculation itself is mechanical once you’ve chosen your reference book and method.

For more on the no-vig prices that come out of devigging, see No-Vig Odds. For the broader strategy that devigging supports, see Positive EV (+EV) and +EV Betting Explained.