Devig Calculator
Remove the bookmaker margin from any market and compare fair probabilities from five devig methods: multiplicative, additive, power, Shin and worst case.
How to use this calculator
Enter the odds for every outcome of one market: both sides of a moneyline, all three results of a soccer match, or every runner in an outright. The calculator shows the overround, the margin, and each outcome's fair probability under five devig methods, one at a time or side by side. Every method needs the full market; one price alone cannot be devigged.
Use the check a price panel to enter odds you are offered elsewhere. The calculator compares them with the fair probability from each method and reports your edge, expected value and Kelly stake.
What the vig is
A bookmaker's prices are not probabilities. Convert each price to an implied probability with 1 / decimal odds and add them up: the total exceeds 100%. The excess is the overround, and the bookmaker's margin is what that overround is worth as a share of turnover. A standard -110 / -110 market implies 52.38% on each side, 104.76% in total, an overround of 4.76% and a margin of 4.55%.
Devigging (removing the vig) means shrinking those implied probabilities back to a set that sums to 100%. The catch is that the bookmaker never says how the margin is spread across the outcomes, so every method has to assume something, and the assumptions disagree exactly where it matters: on markets with a favourite and a longshot.
Why the method matters
On a symmetric market every method gives 50 / 50. On a market with a clear favourite they diverge. Take a two-way market at 1.30 and 3.75, an overround of 3.59%:
| Method | Favourite | Underdog | Fair odds |
|---|---|---|---|
| Multiplicative | 74.26% | 25.74% | 1.35 / 3.88 |
| Additive | 75.13% | 24.87% | 1.33 / 4.02 |
| Power | 75.59% | 24.41% | 1.32 / 4.10 |
| Shin | 75.13% | 24.87% | 1.33 / 4.02 |
| Worst case | 74.26% | 24.41% | 1.35 / 4.10 |
The underdog's fair probability ranges from 24.41% to 25.74% depending on the method: a difference of 1.3 points, which is more than the edge on most bets. A price of 4.00 on the underdog is value under multiplicative and a losing bet under power. Open this market with the price check filled in to see the disagreement in EV terms.
The five methods
- Multiplicative divides every implied probability by their sum, removing the same proportion from every outcome. Simple and standard, but bookmakers shade longshots more than favourites, so it overstates the chance of longshots. Fine for symmetric markets.
- Additive subtracts an equal number of percentage points from every outcome: a heavier proportional cut on longshots, closer to how books price, but on a large field it can push a longshot below zero. The calculator clamps such values and flags them.
- Power raises every implied probability to the same exponent
k, chosen so the results sum to one. The cut grows as the price lengthens, matching the favourite-longshot bias in bookmaker prices. Usually the best single choice for uneven markets. - Shin models the overround as protection against insiders who know the result and solves for the insider share
z. It typically lands near additive on two-way markets, and a largezpoints to a market where the book expects informed money. - Worst case takes, for each outcome, the lowest fair probability any other method produced. It does not sum to 100% and is not meant to: a price that shows value against it shows value under every model.
From fair odds to expected value
The fair probability is the input to every value calculation. Compare it with a price you are offered: EV per unit = p × odds − 1. On a soccer market at 2.20 / 3.40 / 3.60 the Shin method puts the home win at 44.50%. If another bookmaker offers 2.40 on the home win, the expected value is 0.445 × 2.40 − 1 = 0.068, an edge of 6.8%, and the Kelly stake is 4.86% of bankroll. The price-check panel does that arithmetic under each method at once, and the EV & Kelly calculator turns the result into a stake from your bankroll.
Two rules keep this honest. Devig the sharpest market you can find: devigging a recreational bookmaker recovers that bookmaker's opinion, not the truth. And when the methods disagree, use the one that has matched closing lines on that market type, or the worst case.
Frequently asked questions
Which devig method should I use?
Multiplicative for symmetric markets such as -110 / -110, where every method agrees. For a clear favourite, three-way soccer or an outright, power or Shin usually match closing lines better. If the bet is marginal and you are unsure, use the worst case.
Why do the methods disagree?
Because the vig is not spread evenly. Bookmakers shade longshots more, so each method's assumption about where the margin sits changes the answer most where the odds are longest. On a 2.6% overround the methods differ by a few tenths of a point; on an 18% outright they differ by several points.
Can I devig a three-way market?
Yes. Add a third leg and enter all three prices; every method works on any number of outcomes. A market with a draw needs all three results, not just the two teams, or the sum is meaningless.
Does devig work on exchange prices?
Yes, and it is a good source of fair odds. Exchange prices carry a small overround set by traders rather than a bookmaker margin. Devig both sides, then remember that the price you actually get on the exchange is after commission; the commission calculator shows the effective price.
The formulas and a comparison on three markets are in Devig methods explained; the odds converter gives the implied probability of a single price.