Devigging Methods Explained: Power, Shin, Additive, Multiplicative

Devigging is the process of removing the sportsbook's margin (vig) from published odds to estimate the true probability of each outcome. Every sportsbook inflates their odds so the implied probabilities add up to more than 100%. That excess is the vig. Stripping it away gives you fair odds you can use to identify +EV bets.

The question isn't whether to devig. It's which method to use. Different methods distribute the vig removal differently across outcomes, and the choice matters more than most bettors realize, especially in lopsided markets.

Why the method matters

Consider a market priced at -300 / +240 (heavy favorite / underdog).

The implied probabilities are:

• Favorite: 75.0%
• Underdog: 29.4%
• Total: 104.4% (4.4% vig)

We need to remove that 4.4% to get fair probabilities that sum to 100%. But how do we distribute the removal? Do we take the same amount from each side? A proportional amount? Something weighted toward one side?

Each method answers this differently, and the resulting fair odds can diverge by several percentage points on lopsided lines. On tight lines (-110 / -110), all methods produce nearly identical results. The differences only matter when there's a large gap between favorite and underdog.

The four main methods

Multiplicative (proportional)

The most common method. Each implied probability is divided by the total overround so the probabilities scale proportionally to 100%.

Formula:

Fair probability = Implied probability / Total implied probability

Example (-300 / +240, total = 104.4%):

• Favorite: 75.0% / 104.4% = 71.84%
• Underdog: 29.4% / 104.4% = 28.16%

Multiplicative removes the same proportion of vig from both sides. This assumes the vig is distributed evenly relative to each side's probability. It's a reasonable default and the simplest to calculate.

When to use: General-purpose default. Works well on balanced markets and two-way markets where neither side is a heavy favorite.

Weakness: Research suggests sportsbooks actually load more vig onto longshots than favorites (the favorite-longshot bias). Multiplicative ignores this, which means it may underestimate the true probability of favorites and overestimate underdogs in lopsided markets.

Additive (equal margin)

Subtracts an equal amount of vig from each outcome's implied probability.

Formula:

Fair probability = Implied probability - (Overround / Number of outcomes)

Example (-300 / +240, overround = 4.4%, two outcomes):

• Favorite: 75.0% - 2.2% = 72.80%
• Underdog: 29.4% - 2.2% = 27.20%

Additive removes the same absolute amount from each side. This shifts the favorite's probability up less (relatively) and the underdog's probability down more (relatively) compared to multiplicative.

When to use: Rarely the best choice. It doesn't account for the fact that sportsbooks typically add more vig to longshots. However, it's simple and can be useful as a sanity check against other methods.

Weakness: Treats all outcomes as if they absorb equal vig, which doesn't match how sportsbooks actually set lines.

Power method

Uses an exponent to adjust each probability such that the proportional relationship between outcomes changes based on the size of the margin. The favorite absorbs relatively less vig, the underdog absorbs more.

Formula:

Find exponent k such that: p1^k + p2^k = 1
where p1, p2 are the implied probabilities

This requires iterative solving (no closed-form solution), which is why a devig calculator handles it for you.

Example (-300 / +240):

• Favorite: 72.47%
• Underdog: 27.53%

The power method sits between multiplicative and Shin. It adjusts for the favorite-longshot bias more than multiplicative but less aggressively than Shin.

When to use: A strong general-purpose method. Many professional bettors and betting tools use power devig as their default because it handles the favorite-longshot bias reasonably well without overcorrecting.

Shin method

Based on academic research by Hyun Song Shin (1993), this method models the sportsbook margin as resulting from the presence of inside information in the market. It assumes informed bettors (insiders) create a predictable pattern in how vig is distributed: more vig on longshots, less on favorites.

Formula:

The Shin method solves for parameter z (representing the proportion of informed bettors) in:

Sum of: (sqrt(z^2 + 4*(1-z)*pi^2/o) - z) / (2*(1-z)) = 1
where pi = implied probability, o = overround

Again, this requires iterative solving.

Example (-300 / +240):

• Favorite: 73.05%
• Underdog: 26.95%

Notice how Shin gives the favorite the highest fair probability and the underdog the lowest, compared to all other methods. It corrects most aggressively for the favorite-longshot bias.

When to use: Best for markets where the favorite-longshot bias is strongest: horse racing, futures markets with many outcomes, and heavily lopsided two-way markets. Shin was originally developed for horse racing betting where the bias is most pronounced.

Weakness: Can overcorrect on markets where the favorite-longshot bias is minimal (balanced spreads, -110/-110 markets). In these cases, it's functionally identical to other methods anyway.

Shin vs. Power on 2-way markets: For binary outcomes, Power and Shin produce nearly identical results. Even on a lopsided -500/+350 line, they diverge by less than 1 percentage point. The meaningful differences between the two only appear on 3-way markets (soccer 1X2) and multi-runner markets (futures, horse racing) where Shin's insider-trading model distributes vig across many outcomes differently than the Power exponent.

Method comparison

Here's how the four methods compare across different market types:

Balanced market (-110 / -110)

On balanced markets, all methods produce identical results. The choice doesn't matter here.

Moderate favorite (-200 / +170)

Differences start appearing but are small. The range between methods is under 0.6 percentage points on the favorite. On moderately lopsided markets like this, the method choice barely matters.

Heavy favorite (-500 / +350)

Now the methods diverge meaningfully. Multiplicative gives the underdog the highest fair probability (21.05%) while additive and Shin give the favorite more credit. The gap between methods is 1-2 percentage points, which matters when deciding whether a bet is +EV. Use our no-vig calculator to compare all methods side by side for any market.

Which method should you use?

For most two-way sports markets (NFL spreads, NBA totals, tennis): Power method is the best general default. It accounts for the favorite-longshot bias without overcorrecting.

For three-way markets (soccer 1X2): Multiplicative or power. The draw in soccer doesn't behave like a traditional "longshot," so Shin's insider-trading model is less applicable.

For futures and multi-outcome markets: Shin or power. These markets have the strongest favorite-longshot bias because the field of outcomes includes many longshots where vig gets loaded.

For sharp markets (Pinnacle): Method matters less because Pinnacle's margins are so small (1-3%) that the methods converge closely. Pinnacle's own article on margin calculation explains why their low-margin approach makes devig method choice less critical. Multiplicative is fine.

For high-vig retail markets (DraftKings props, 8-15% vig): Method matters more because there's more vig to distribute. Use power or Shin for the most accurate fair odds.

Our no-vig calculator supports all four methods and shows how the results compare side by side.

Devigging in practice

Devigging is step one in the +EV betting workflow:

1. Devig sharp odds (Pinnacle or another sharp book) to get fair probabilities
2. Compare fair odds against the odds offered at retail sportsbooks
3. If the retail odds are better than fair: the bet has positive expected value
4. Size the bet using Kelly criterion or flat staking

Bet Hero does this automatically: devigging Pinnacle's odds, comparing them against 400+ sportsbooks, and flagging the bets where retail books are offering better prices than fair value.