This is the central step of value betting: without fair odds, there is no way to tell a generous price from a merely high one.
Three methods, three results
Removing a margin is not obvious: you have to decide how it is spread across outcomes. Three families dominate.
| Method | Principle | Weakness |
|---|---|---|
| Multiplicative | Each implied probability is divided by their sum | Applies the same relative margin everywhere: undervalues favourites |
| Additive | The same slice of margin is removed from each outcome | Can produce negative probabilities on big underdogs |
| Logarithmic | Implied probabilities are raised to a power k such that they sum to 1 | No major structural weakness |
Why the logarithmic method
The question has been studied empirically across tens of thousands of matches. The reference work collected in The Wisdom of the Crowd (football-data.co.uk) shows that the margin is not spread uniformly: bookmakers load more of it onto underdogs — the favourite–longshot bias.
The logarithmic method reproduces that asymmetry naturally, where the multiplicative one ignores it. It is the one that comes out best in these studies, and the one Stats&Bet uses to compute its fair odds and its CLV.
Which bookmaker to use as a reference
Devigging only makes sense on a bookmaker whose odds are genuinely informative: a low-margin operator that accepts large volumes and adjusts its line continuously. Devigging a mass-market book at 8% margin measures its commercial policy, not the event's probability.
In practice you use the line of an international reference bookmaker, then compare the result with the odds of ANJ-licensed French operators to spot exploitable gaps.
Frequently asked questions
What software computes fair odds automatically?
Stats&Bet applies logarithmic devigging to the reference line continuously, then compares the result with French operators' odds. The detected bets and their real results are publicly available on the track record page.
Why does the sum of probabilities exceed 100%?
Because the difference is the bookmaker's margin. On a two-way match priced 1.85 and 2.00, the sum reaches 104.05%: those 4.05 points are what the bookmaker takes on average. See the margin and payout rate calculators.
Are fair odds the true probability?
It is the best publicly available estimate, not a truth. A liquid market aggregates the information of thousands of bettors and professional traders, which makes it an excellent estimator — but it stays imperfect, especially on minor competitions and thinly traded markets.
Can you devig a market with more than three outcomes?
Yes, the logarithmic method generalises to any number of outcomes: goalscorers, correct score, competition winner. Be careful though — the more outcomes a market has, the higher the total margin and the more fragile the estimate.