Fair odds: how to remove the vig and find no-vig prices

Every sportsbook market has a margin built into its prices. Fair odds are those same prices with the margin taken out: the price each outcome would have if the market added up to exactly 100%. You will also see them called no-vig or no-margin prices.

Fair odds give you a yardstick. Once you know roughly what an outcome is worth, you can see which prices sit above or below that line. This guide shows how to remove the margin by hand, then how OddsKeepr builds a consensus fair price from many sportsbooks.

Why prices add up to more than 100%

Turn each price into an implied probability and add them up across a market. A sportsbook's market almost always comes to more than 100%. The extra is the sportsbook's margin, also called the vig or juice; measured this way it is called the overround. The what the vig is guide covers it in detail.

Removing the margin means scaling those probabilities back down so they total 100%, then turning them back into odds.

Removing the margin in three steps

1. Find each implied probability. For decimal odds that is 1 ÷ odds.
2. Add them up. The amount over 100% is the overround, one way of measuring the margin.
3. Divide each probability by the total. That gives the fair probability. The fair decimal price is 1 ÷ fair probability, which is the same as the original price × the total written as a decimal (1.0434 for 104.34%).

This is the proportional method: it takes the same share off every outcome's probability. It is simple, it works for any number of outcomes, and it is the method OddsKeepr uses.

A two-way example

A game priced at 1.80 and 2.05:

• Implied probability: 1 ÷ 1.80 = 55.56% and 1 ÷ 2.05 = 48.78%
• Total: 104.34%, an overround of 4.34%
• Fair probability: 55.56 ÷ 104.34 = 53.25% and 48.78 ÷ 104.34 = 46.75%
• Fair price (to three places): 1.80 × 1.0434 = 1.878 (-114) and 2.05 × 1.0434 = 2.139 (+114)

Each side keeps its place, the favourite stays the favourite, and both fair prices are a little longer than the sportsbook's.

A three-way example

Football (soccer) match odds have a draw, so all three outcomes go into the sum:

The overround is 4.81%. Each fair price is the original price × 1.0481: for the home side, 2.10 × 1.0481 = 2.20. The fair probabilities add up to 100% (99.99% here only because of rounding).

Try your own prices in the calculator:

What to include

The method only works on a complete market:

• Three-way markets need the home win, the draw and the away win. Leaving out the draw makes the total fall below 100% and the fair prices wrong.
• Spreads and totals need both sides on the same line. Over 45.5 and Under 46.5 are different markets and cannot be combined.
• Prices from the same moment. Mixing an old price with a new one blends two different markets.

From one sportsbook to a consensus

No-vig prices from a single sportsbook tell you what that sportsbook thinks, minus its margin. Another sportsbook may see the same game a little differently. A consensus fair price combines many sportsbooks so that no single view decides it.

OddsKeepr builds it in two steps:

1. Take the median price for each outcome across the sportsbooks that price the market. The median is the middle value (the average of the two middle values when the number of sportsbooks is even), so one unusual price cannot pull it far.
2. Remove the margin from those median prices with the proportional method above.

Here is a two-way market at five sportsbooks:

The medians are 1.85 and 2.00. Each outcome's median is found on its own, so in general the two can come from different sportsbooks. Then:

• Implied: 1 ÷ 1.85 = 54.05% and 1 ÷ 2.00 = 50.00%, a total of 104.05%
• Fair probability: Team A 54.05 ÷ 104.05 = 51.95%, Team B 50.00 ÷ 104.05 = 48.05%
• Fair price (to three places, so the gap to the nearest prices shows): Team A 1.85 × 1.0405 = 1.925 (-108), Team B 2.00 × 1.0405 = 2.081 (+108)

Book 3's 2.10 on Team B is above the fair 2.081, so it pays more than the consensus says Team B is worth. Every Team A price is below the fair 1.925. The expected value guide shows how to put a number on that kind of gap.

On OddsKeepr, the fair price uses sportsbooks only. Exchange prices are left out of it, because an exchange's listed prices come before any fees it charges and are set by its users rather than by a sportsbook (see betting exchanges).

Limits of fair odds

• It is an estimate. Fair odds describe what the market thinks, not what will happen.
• The margin is not always spread evenly. Some sportsbooks put more of it on long shots than on favourites. Other methods, such as the power or Shin methods, try to model this, and they give slightly different fair prices for big underdogs. For most two-way markets the difference is small.
• Thin markets are noisier. With only a few sportsbooks, or a market that just opened, the consensus moves more. Line movement explains why prices change. Closing line value compares your price with the closing price, ideally with its margin removed, just before the event starts; in thin markets that is a weaker yardstick too.

Betting always carries a risk of losing money, so if you bet, set a limit you are comfortable with and check that the sportsbook is licensed where you are. If gambling stops feeling like entertainment, free and confidential help is listed for every country under where to get help.