What is devigging in sports betting?
Devigging is removing the bookmaker’s margin from a set of prices to recover the probabilities the market actually believes. Both sides of a posted market include the vig, so their implied probabilities sum to more than 100%. A devig scales them back down so they sum to exactly 100% — and those cleaned-up numbers are the fair probabilities every EV calculation depends on.
You cannot compute an edge without one. Comparing your model’s probability to a raw price mixes the margin into the comparison. Devig the market first, and the comparison becomes apples to apples: your estimate versus the market’s estimate.
The multiplicative method
The standard approach for two-way markets is multiplicative devig: convert each side to implied probability, add them, then divide each by the total. A −150/+130 market implies 60.0% and 43.5% for a total of 103.5%; dividing each by 1.035 yields 58.0% and 42.0%. The margin is removed in proportion to each side’s probability, which keeps the ratio between the two prices intact.
Other methods exist — additive devig subtracts the overround evenly, and power devig fits an exponent — and sharp bettors sometimes prefer them for heavy favorites. For the two-sided prop markets this site covers, multiplicative is the convention: simple, symmetric, and honest about its assumptions.
When to devig
Any time you compare anything to a market price. Estimating a pitcher’s strikeout probability? Devig his K market across the sharpest book you can see, then compare. Building fair odds from scratch? Devig a liquid market to sanity-check your model. The OddsGuy board devigs every market before ranking a single prop, which is why its EV% figures are comparable across books that post different prices. Skip the devig and you are grading your estimate against a number padded with margin — the surest way to invent edges that do not exist while missing the ones that do.
Worked example — multiplicative devig of −150 / +130
- Implied: over −150
- 150 ÷ 250 = 60.0%
- Implied: under +130
- 100 ÷ 230 = 43.5%
- Overround
- 60.0% + 43.5% = 103.5%
- Fair over
- 60.0% ÷ 103.5% = 58.0%
- Fair under
- 43.5% ÷ 103.5% = 42.0%
- Fair odds
- 58.0% → −138 · 42.0% → +138
Stripped of margin, this market believes the over is a 58.0% shot worth −138. Any book still dealing better than −138 on the over is dealing a +EV price.
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Related terms
Frequently asked questions
Why multiplicative devig instead of other methods?▾
Multiplicative devig removes margin in proportion to each side’s implied probability, which preserves the market’s odds ratio and treats favorite and underdog symmetrically. Additive devig can push longshot probabilities negative, and power devig needs an extra assumption. For two-way props, multiplicative is the accepted default.
Do devigged probabilities equal true probabilities?▾
Not exactly — they equal the market’s probabilities, margin removed. The market is usually the best single estimate available for liquid events, but it still carries the opinions and liabilities of the crowd. Devig gives you a fair benchmark to compare against, not an oracle.
Which book should I devig?▾
The sharpest, most liquid market you can see — exchanges and low-margin books lead, soft books follow. Many bettors devig a consensus of several sharp books to average out book-specific liabilities. The noisier the market, the more books you want in the average.
Can I devig a market with more than two outcomes?▾
Yes. The same multiplicative recipe works for any number of mutually exclusive outcomes: convert each to implied probability, sum them, divide each by the sum. It is common for futures and outright markets where the overround is much larger than on a two-way prop.
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