"Devigging" means removing the sportsbook's margin from a set of odds to recover fair probabilities. It is the step that turns a sharp book's price into a fair line you can compare against every other book. There is more than one way to do it, and the method matters most for favorites and longshots.
The problem
A sharp market shows −200 / +170.
- −200 → 66.67%
- +170 → 37.04%
- Total: 103.70%
We know the true probabilities add to 100%. The question is how to take away the extra 3.70%. Should each side lose the same share, the same amount, or should the longshot lose more?
Method 1: Multiplicative (proportional)
Divide each implied probability by the total.
- 66.67 ÷ 1.037 = 64.29%
- 37.04 ÷ 1.037 = 35.71%
Simple and the most common. It assumes the margin is spread in proportion to each side's probability.
Method 2: Additive
Subtract an equal share of the overround from each side.
- 66.67 − 1.85 = 64.82%
- 37.04 − 1.85 = 35.19%
It gives the favorite slightly more probability. It can produce strange results (even negative probabilities) on extreme longshots, so it is rarely used alone for big underdogs.
Method 3: Power
Find an exponent k so that each implied probability raised to k sums to 1. Here k ≈ 1.059:
- 0.6667^1.059 ≈ 65.1%
- 0.3704^1.059 ≈ 34.9%
(Small rounding aside, the two add to 100%.) The power method takes proportionally more margin from longshots, which matches a well-known pattern: bettors overpay for longshots (the favorite-longshot bias), so books load more margin there.
Method 4: Shin
Shin's method models a market where some bettors have inside information, and the book protects itself by shading longshots. It is more involved to calculate, but in two-way markets it typically lands close to the power method. It is especially popular for multi-runner markets like horse racing and golf.
Comparing the results
| Method | Favorite | Underdog | Fair odds (dog) |
|---|---|---|---|
| Multiplicative | 64.29% | 35.71% | +180 |
| Additive | 64.82% | 35.19% | +184 |
| Power | ~65.1% | ~34.9% | ~+186 |
The difference looks small, but if another book offers +185 on the underdog, the multiplicative method calls it +EV (about +1.8%) while power calls it slightly −EV. Method choice decides whether you bet.
Which method should you use?
- Near-even markets (−120 to +120): all methods agree closely. Use multiplicative.
- Favorites vs big underdogs: power or Shin usually fit real-world results better.
- Multi-outcome markets (soccer 3-way, futures): power or Shin.
- When in doubt: calculate all of them and use the worst case for your side. If the bet is still +EV under the least favorable method, it is a much safer edge.
That last approach is what OddsHype does: it devigs every sharp market with all four methods and reports the least favorable edge, so the number you see is the conservative one. (Fair odds explained.)
Devig one side or both?
You need both sides of the market (or all outcomes) to devig properly. If a sharp book only shows one side of a prop, you cannot cleanly remove the margin; you can only assume a typical margin, which is much less reliable.
Try it
Plug any two-way or three-way market into the no-vig fair odds calculator to see fair probabilities and fair American odds instantly.
Frequently asked questions
What does devig mean in sports betting?
Devigging means removing the sportsbook's built-in margin from a set of odds to estimate the true (fair) probability of each outcome.
What is the best devig method?
For near-even markets the methods agree. For favorites and longshots, the power and Shin methods are generally more accurate. Using the worst case across methods is the most conservative approach.
Why does devigging matter for +EV betting?
Your edge is measured against the fair line. A wrong devig can turn a −EV bet into an apparent +EV bet, especially on underdogs.