What Are Fair Odds & How To De-Vig A Betting Line

When you’re in the world of +EV betting an important concept to understand is Fair Odds for a given betting market. It’s also important to understand that fair odds aren’t necessarily true odds but rather an estimate of what the odds or price should be compared to the price being offered by a sportsbook or DFS platform.

Understanding Fair Odds

A simple way to translate this concept is when you go to the grocery market and remark how expensive eggs are this week and come to the conclusion “I’m not paying that price, eggs should only be $2.15 a dozen.” You quickly realize that the grocery store has charged a higher price, increasing their revenue while hurting you, the consumer. The fair price could be $2.15 in your opinion compared to the $3.50 price being offered at the store.

Now, when looking at sports betting the same idea can be applied. How often do you quickly scan the odds for a given week’s NFL slate and start licking your chops at some opportunities saying to yourself “why are the Cowboys -250 today on the road at Philly, they should be -175,” that -175 may be YOUR fair odds for that market but may not be the objective correct price which we will look at down below.

However, we can take a step further by using actual math to calculate a fair odds price using a method called de-vigging.

De-Vigging A Betting Price

If you take the concepts above, notably the super market example, you can start to see where there is a markup that you’re expected to pay, this is called the “vig” or “juice.” Sportsbooks build vig into their odds to create a mathematical edge for themselves over time.

Take a -110/-110 betting line for example, a pick’em, such as coin flip odds for the Super Bowl. A coin flip, as you know, is a 50/50 outcome but the implied odds of a -110 line is actually 52.4% meaning the Heads would have to hit more than 52.4% of the time for you to be profitable in that market compared to the fair odds of +100 or 50% implied odds.

That difference from +100 to -110 is the vig, some also say 10 cents of juice. Understanding and seeing the sportsbooks’ built-in vig allows you to understand the fair odds easily and then identify good +EV opportunities as books may offer closer to fair odds or even better than fair odds, let's say +105 in this case, which in the long run is a profitable strategy for you.

Let’s take this a little further with implied probability and de-vigging as the two work hand in hand. In the above -110 / -110 coin flip example, it’s quite simple to de-vig to +100 or 50/50 but as you know, sportsbooks have all kinds of lines such as Dak Prescott 256.5 passing yards with OVER odds at -130 and UNDER odds of +110. A -130 line represents an implied win probability of 56.5% and a +110 line gives 47.6% implied win probability but if you add these two together it’s 104.1% – that 4.1% is essentially the sportsbook’s built-in margin as the fair odds for a market should land at 100%.

But you can’t just simply subtract 4.1% or 2.55% on either side as the odds to have a proportionate relationship to one another, so you can keep that relationship by dividing the sportsbook implied probability 56.5% for the over by the overall sportsbook 104.14% = 54.27% and the same for the under which gives you 45.73% and these would be your fair probabilities. You can use our no-vig calculator to put in odds and get fair probabilities.

Now you can take your new fair probabilities and plug them into our odds converter calculator to get your fair odds which would be -119 for the OVER and +119 for the UNDER and if a book was offering -105 odds for the OVER that would be about a 6% expected return relative to your bet. This is one method of de-vigging.

Understanding fair odds and de-vigging is very important and the examples above are how you do it at singular levels, but also have to consider that sportsbooks offer all sorts of OVER and UNDER lines that present different vigs and implied probabilities. Take the example above at one sportsbook, let's say DraftKings but then FanDuel offers the OVER at -130 but the UNDER at +120. Do the same math and FanDuel’s implied probability equals 101.95% and the fair odds there would be -124 for the OVER and +124 for the UNDER. This to say the fair value for the UNDER is likely somewhere between +119 and +124 for these two books but of course there are lots of books to consider.

Good thing for you, our elite algorithms and +EV tools take many different books into account and identify fair odds so you don’t have to do the math then examine all the odds to provide you the best +EV opportunities available.