How it works
A sportsbook’s two prices on a market imply chances that add up to more than 100%. Taking the margin out, or devigging, scales them back to exactly 100%: the market’s fair view of each side, and the fair price that goes with it.
There is more than one way to share the margin out. The multiplicative method divides each chance by their total, so each side gives up margin in proportion to its size. The power method raises both chances to the one power that makes them add up to 100%, which takes more of the margin from the longshot. That suits lopsided markets, where longshots tend to be priced shorter than their chance: the favorite-longshot bias. On a close market the two methods barely differ.
The formula
Implied chance: p = 1 ÷ decimal, for each side
Multiplicative: fair = p ÷ (pA + pB)
Power: fair = p^k, with k chosen so that pA^k + pB^k = 1
Fair price = 1 ÷ fair chance
A worked NFL example
An NFL moneyline at −150 / +130. The implied chances add up to 103.48%, a margin of 3.48%.
| Favorite | Underdog | |
|---|---|---|
| Implied, margin in | 60.00% | 43.48% |
| Multiplicative | 57.98% | 42.02% |
| Power | 58.40% | 41.60% |
| Fair price, multiplicative | −138 | +138 |
The multiplicative method takes 2.02 points off the favorite and 1.46 off the underdog. The power method takes more from the underdog: 1.88 points, against 1.60 from the favorite. On a lopsided line the gap grows. At −400 / +300, multiplicative gives 76.19% / 23.81% and power gives 78.24% / 21.76%.
Common mistakes
- Mixing books or markets. Both prices need to come from the same book, the same market and the same moment. One book’s favorite and another’s underdog aren’t one market.
- Using it on a three-way market. This calculator takes two prices. A market with a third outcome, like a soccer result with the draw, needs all three in the math.
- Reading the fair chance as an edge. It is the market’s view with the cut removed, not a forecast and not a bet. A bet has value only when your own chance beats the price you can get: the expected value calculator shows by how much.
- Ignoring the method on long prices. On the −400 favorite above, the two methods are 2.04 points apart. That is enough to turn a small edge into none.
In Unitley
Unitley compares the books it tracks at FanDuel’s line, to show the best price on offer and a no-vig chance from their consensus. How Unitley gets its prices.