The vig explained: how de-vigging finds fair odds

Bottom line: Every set of odds carries a hidden margin (the vig, or overround), which is why a market's implied probabilities sum to more than 100%. De-vigging removes it, rescaling the probabilities back to a true 100% so you're left with the market's genuine, fair estimate. It's the step that turns a raw price into an honest number, and it's the heart of the market line served by the EsportsOdds CS2 data API. This page also shows, step by step, how to remove the vig from odds by hand.

What the vig is

The vig (short for vigorish, also called the overround or margin) is the edge built into a set of odds. It's the reason the implied probabilities of a market don't add up to 100%: they add up to a bit more, and that surplus is the margin.

Take a match priced at 1.90 on each side. Each implies 52.6%, and together they sum to 105.2%, so this market carries a 5.2% vig:

A tighter market might carry a 2% margin; a wider one 8% or more. The size of the vig tells you how much "padding" is in the price, and the whole point of de-vigging is to take it back out so you can see the fair probability underneath. Margins tend to be widest where a book is least certain: a thinly-traded market or an early line usually carries more padding than a popular match-winner market, because the book is charging for its own uncertainty as well as its edge.

How de-vigging works

The simplest and most widely used method is multiplicative (also called proportional or normalisation): divide each outcome's implied probability by the market total. Here's a worked example with an uneven market, Team A at an implied 60%, Team B at 45%, summing to 105%:

Divide each by the total (1.05) and you get 57.1% and 42.9%, which now sum to exactly 100%. Each outcome keeps its share of the market; only the inflated total is removed. That pair of numbers is the fair, de-vigged line.

There's a second common method, additive, which splits the margin equally across outcomes rather than proportionally. On the same 60/45 market it nudges the favourite slightly higher, to 57.5%, and the underdog to 42.5%:

The two agree closely here, and both sum to 100%. Additive can be a better fit for lopsided markets and handles the favourite-longshot bias a little differently, but multiplicative is the standard starting point and is what most people mean by "no-vig" odds. Which method to use is a small but real modelling choice, one the forecasting literature has studied directly (for example Štrumbelj's 2014 comparison of de-vigging methods).

How to remove the vig from odds, step by step

The example above started from probabilities, but a real market starts from prices. Here are four steps from a price to a fair price, using a −110/−110 market.

1. Turn each price into a probability. Use these rules, or the implied probability calculator.
   • Decimal: 1 ÷ price.
   • Positive American: 100 ÷ (price + 100).
   • Negative American: drop the minus sign, then divide that number by (that number + 100). So −110 gives 110 ÷ (110 + 100) = 52.38%.
2. Add the two probabilities. 52.38% + 52.38% = 104.76%, called the booksum. The part above 100% is the margin, or vig, here 4.76 points.
3. Divide each probability by the booksum. 52.38% ÷ 1.0476 = 50.00% each.
4. Turn the fair probability back into a price. Let p be the probability as a decimal (0.50 for 50%).
   • Decimal: 1 ÷ p.
   • American: −100 × p ÷ (1 − p) if p is above 0.50, otherwise +100 × (1 − p) ÷ p.
   • Here p = 0.50, so the fair price is 2.00 (decimal) or +100 (American).

Now a lopsided market, −250/+200. Step 1 gives 71.43% for −250 (250 ÷ 350) and 33.33% for +200 (100 ÷ 300). The booksum is 104.76% again. Dividing by 1.0476 leaves fair probabilities of 68.18% and 31.82%. Step 4 gives fair decimal prices of 1.47 and 3.14.

For American odds, both sides use 68.18 ÷ 31.82 × 100, about 214. Above 50%, the favourite gets a minus sign: −214. Below 50%, the underdog gets a plus sign: +214. In a two-way market, fair American prices are a mirror pair, one minus and one plus of the same size, unless the market is exactly even, where both are +100.

To check, add the fair probabilities back up. They should total 100%, allowing for rounding. If not, you slipped when adding or dividing in steps 2 and 3. The check can't catch a mistyped price, because dividing by the booksum forces the total to 100% whatever you typed.

With the multiplicative method, the favourite's correction differs by market. All three markets below total 104.76%, the same margin. Dividing by 1.0476 cuts every probability by the same share, about 4.5%, so the bigger probability loses more points. In each of these markets the pair loses the same 4.76 points, so as the favourite's share of the cut grows, the underdog's shrinks. In row one the sides are equal, so the table shows one of them.

Other methods of de-vigging split the cut differently: additive, power and Shin. At −600/+425, the +425 side's fair probability is 18.18% (multiplicative) or 15.77% (power), a spread of 2.41 points. See how the four methods compare.

Why the fair line matters

A de-vigged probability is the honest one, the market's genuine estimate with the house edge stripped out. That makes it the right number for two jobs:

• Comparing the market to a model. If you have your own view of a match, you want to compare it against the market's fair probability, not a padded price. De-vigging puts both on the same footing.
• Measuring line movement cleanly. Concepts like closing line value (how a price moved between when you looked and when the match started) only make sense against de-vigged numbers, because otherwise you're measuring changes in the margin as well as changes in opinion. If you noted a fair 55% and the line later closed at a fair 60%, the market shifted five points toward that outcome after you looked. Measured on raw prices, part of that shift would just be the book widening or tightening its margin, which is noise rather than signal.

Neither of those is a tip or a recommendation. They are analysis. De-vigging is a data-cleaning step, the same way you'd normalise any other measurement before comparing it.

How EsportsOdds builds a de-vigged line

Doing this well across a whole match schedule is the work the EsportsOdds market line automates. Rather than trust a single source, it takes prices from multiple bookmakers and exchanges, de-vigs each one, takes the median across them, re-normalises so the outcomes still sum to 100%, and publishes one fair number with no individual source ever named:

Each source is de-vigged first, so a source that quotes a wider margin has that margin removed before it is combined. The output is a market-implied win probability you can pull as JSON on a flat $99/month plan, already de-vigged and ready to compare against your own model.

As a check of the pipeline, on 28 October 2026 we looked at each open market that has a market line: 56 markets with two outcomes each. Taking 1 divided by the published price for each outcome, the implied probabilities summed to 100.0000% in all of them.

Once you understand the maths, reading the line itself is a single request. The guide to reading the CS2 market odds line via the API walks through the endpoint, the response shape, and how to turn it back into a probability.

Frequently asked questions

What does "de-vig" mean?

De-vigging (or "no-vig") means removing the bookmaker's margin from a set of odds so the implied probabilities sum back to a true 100%, leaving the fair probability of each outcome. It's a standard data-cleaning step for anyone analysing markets.

What is the vig or overround?

The vig (vigorish), overround, or margin is the edge built into odds, the reason a market's implied probabilities add up to more than 100%. A 1.90/1.90 two-way market carries about a 5.2% vig.

How do you calculate no-vig odds?

The simplest way is the multiplicative method: convert each outcome to its implied probability, sum them, then divide each by that sum. For 60% and 45% (total 105%), the fair probabilities are 57.1% and 42.9%.

How do you remove the vig from −110/−110 odds?

Each side has an implied probability of 52.38%, so the pair adds to 104.76%. Dividing each side by 1.0476 gives 50.00% each. That is a fair price of 2.00 in decimal odds, or +100 in American odds.

Is de-vigging the same as finding fair odds?

Yes. The de-vigged probabilities are the "fair" odds, meaning the odds with no margin. They represent the market's genuine estimate of each outcome's likelihood.

Where can I get de-vigged odds via an API?

The EsportsOdds CS2 data API serves a de-vigged market-implied win probability per match, aggregated as the median across multiple sources with no book named, on a flat $99/month plan. You get the fair number directly, so the only maths left on your side is comparing it to your own view.

Want to run the numbers yourself? The free no-vig calculator does exactly what this article describes, and compares all four de-vig methods on the same prices.

Cite this

EsportsOdds, "The vig explained: how de-vigging finds fair odds", 10 July 2026. https://esportsodds.gg/learn/devig-fair-odds

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