How Do Odds And Lines Work?

How Do Odds And Lines Work?

Now that sports betting is legal in a growing list of states, you don’t have to go to Las Vegas to find odds on the games. Here in Illinois, a number of top operators are available.

So, how do the numbers in Illinois compare with what you’ll find in Vegas? Are the odds in Illinois any good? How can you tell if the lines are fair? There are plenty of questions that come up on the topic of sports betting odds, and we’re here to provide the answers.

You can consider this your behind-the-scenes look at how the odds are made. We hope to give you a greater understanding of this important — and often misunderstood — topic.

What are sports betting odds? 

Legal and regulated sportsbooks provide bettors with a safe place to wager on sporting events. For each contest, they’ll provide odds on all selections available to bettors.

The odds tell us the likelihood of an outcome from the oddsmakers’ perspective, and also point us to the price that operators will pay out on winning bets. To understand the odds board, let’s look at a standard listing for an NFL bet:

Team Point Spread Moneyline Total
Minnesota Vikings +2.5 (-110) +120  O 49.5 (-110)
Chicago Bears -2.5 (-110) -140  U 49.5 (-110)

If you read from left to right, you see a series of numbers. These are the odds and lines for three bet types: point spreads, moneylines and totals. In this example, the Bears are favored by 2.5 points and on the moneyline in a game with a projected total of 49.5 points.

We can tell that Chicago is favored due to the negative numbers attached to that side. In the world of sports betting, the odds are negative for favorites and positive for underdogs. In the case of the spread and total, you’ll see numbers for the benchmark number set by oddsmakers and for the actual odds on the bet.

Listings will vary for other wager types, but there will be odds available on all of them, including bets, such as props and futures wagers. After the initial release of odds to the public, the numbers will move. We’ll explain why that happens.

How do sportsbooks set lines?

Each sportsbook has a team responsible for setting the lines. The person who oversees the operation is often referred to as the oddsmaker. To set the numbers, the book has a wealth of data at its disposal to lean on, as well as computers and proprietary algorithms.

In a nutshell, all the factors that could impact the outcome of a contest are factored into the equation. For the NBA, this could be, e.g., defensive efficiency on both sides, while NHL factors include the number of shots that each side has been allowing as of late.

Additionally, every ancillary factor that you can think of is also thrown into the pot, which could include injury concerns, potential weather issues and home-field advantage. After everything is together, the data points are thoroughly analyzed.

That leads to a result that the oddsmaker uses to set lines, which is given a thorough review. Once the odds team is happy with the results, numbers are officially released to the public and wagering begins.

Main types of odds in sports betting

Illinois sportsbooks offer odds on a wide range of sporting events. The most popular sports available for betting are the following:

  • College basketball
  • College football
  • Boxing
  • Golf
  • MLB
  • NBA
  • NFL
  • NHL
  • Soccer
  • Tennis
  • UFC

If you’re looking to bet on a major game or event, you’ll find sportsbook odds available. For those interested in the smaller sports, Illinois sportsbooks usually provide markets for them, too. Offerings may vary, but here’s a general idea of what you’ll see:

  • Australian rules football
  • Cricket
  • Cycling
  • Darts
  • International sports
  • MMA
  • Motorsports
  • Rugby
  • Snooker
  • Table tennis
  • Volleyball

In addition to a wide range of sports, there are also several bet types to sort through for each contest on the docket. Here’s a quick overview of some of the top wager types available.


A moneyline is one of the most basic wagers on the board. You simply have to choose which side you think will win, from the favorite and underdog. Here’s a fictional example:

Cincinnati Reds +110
Chicago Cubs -130

Point spread

Oddsmakers will install a point spread that needs to be factored into decisions. You can choose the favorite minus the points or the underdog plus the spread. Here’s an example:

Detroit Pistons +2.5 (-110)
Chicago Bulls -2.5 (-110)


A totals bet revolves solely around the combined number of points scored in the game. Sportsbooks set a baseline, and you then get to choose the over or under benchmark:

Over 5 (-110)
Under 5 (-110)


A prop or proposition bet is an additional wagering opportunity to consider for games and events. Many prop bets revolve around the statistical performance of individual players. Let’s look at an example:

How many rushing plus receiving yards will David Montgomery have?
Over 79.5 (-135)
Under 5     (+115)

Live betting

Live bets are wagers you can place in real-time as the action unfolds. It’s a fast-moving market in which odds and offerings will vary depending on what’s happening on the field or court. Here’s an example:

What will be the result of this power play?
Power play goal for Blackhawks -140
Penalty kill for Red Wings +120


You can place a futures wager on an outcome that will happen at a later date, such as who will win the Super Bowl. Futures are also available on events such as MLB team win totals, for example:

How many regular-season wins for the Chicago White Sox?
Over 5 (-115)
Under 5 (+105)

These are a few of the ways to wager on sports. You can also place more exotic wagers, such as teasers, parlays and round robins.

However, the offerings and odds may vary by operator. The numbers won’t be the same for each event available for wagering. For example, DraftKings Sportsbook in Illinois may offer more favorable odds on one game than FanDuel and vice versa.

When getting set to place your bets, take the time to compare prices at legal operators here in Illinois. Line shopping is a good habit to get into as you can sometimes find better prices on contests.

Does Las Vegas have the best sportsbook odds?

For decades, those who wanted to legally bet on sports had to plan a trip to Las Vegas. These days, that’s no longer necessary for a number of folks. Sports betting has been legalized in several states, including in Illinois.

Since Vegas effectively had sports betting on lockdown, the numbers that came out of the desert were the gold standard. While the odds at Vegas sportsbooks still deserve respect and consideration, it’s no longer the only word to follow.

Sportsbook operators in legal states offer odds and lines comparable with what is available out west.  You can take the time to see what the oddsmakers in Vegas have to say, but know that you’ll likely find similar numbers here in Illinois.

Do odds get set the same way for all sports?

The overall concept of sports betting odds is the same regardless of what kind of competition. That said, each sport has a set of nuances that are factored into the equation.

As a result, the odds aren’t set in the same fashion for every sport. What moves the needle in the world of the NFL is quite different from the factors that go into a UFC fight, for example.

At the top level, sportsbook oddsmakers are factoring everything that could move the needle on a contest into an equation while setting the odds. Exactly what will have an impact will vary by sport so that naturally translates into differences in the oddsmaking process.

While odds may not be set in the same way for each sport, the way you read them is still the same. In cases where there are two choices, the negative side indicates favorites while positive numbers point to underdogs.

Why do odds change in betting?

Sports betting odds don’t stand still. After the initial release of the numbers to the public, the betting begins. As the public money coming in develops an overall preference, the odds may shift to reflect the activity.

If a sportsbook releases numbers on a game and a flood of bets come in on one side, the book becomes lopsided on that contest. That’s not a situation it wants to be in, so it will tweak the numbers in an attempt to level things out.

This process may continue right up until the time of the event, so it’s not uncommon to see several shifts after the initial release. As part of your research, it’s a good idea to compare the opening lines to the current numbers to understand how the market has shifted.

If one side is more attractive than it was initially, you can take that as a sign that the early money went to the other side. When the odds tighten up further on both sides, it’s a sign that the bets have been relatively even.

What is an odds algorithm?

An odds algorithm is a tool the oddsmaking teams use as they set the numbers. An odds algorithm pulls together all the data and variables that can impact an outcome. Oddsmakers analyze the information with the assistance of computers to assess the most likely outcome.

The team examines the results and will tweak as needed if new information arises afterward. Once the assessment has been completed, oddsmakers will finalize the lines and release them to the public for betting to begin.

The list of information that’s pulled together and analyzed is a lengthy one. Here are some factors that are looked at for a few of the major sports:

  • NFL: Team rushing yards for and against.
  • NBA: Assist to turnover ratio and true shooting percentage.
  • MLB: Starting pitcher past performance against current opponent.
  • NHL: Shots for and against.
  • Golf: Past performance at the current course for all golfers in field.
  • Tennis: Player performance against the current and similar opponents.
  • NASCAR: Recent results and performance on current track.
  • UFC: Fighter performance versus common opponents.

In short, you can think of an odds algorithm as the pot. All the ingredients are put into it, and the algorithm’s job is to deliver the completed recipe. Naturally, the oddsmaking team oversees baking to make sure that everything is edible.

Which Illinois betting sites have the best odds?

As you begin shopping around for the best sports betting odds, you’ll find that many of the top operators will be right in range on the biggest games and events. It’s not uncommon to see the same favorites and underdogs listed everywhere.

However, closer inspection of the numbers can reveal ticks of difference here and there. You may be able to find a better price on an NFL game you’re interested in at PointsBet Sportsbook in comparison to Bet Rivers Sportsbook, for example.

Upon the initial release of lines, many books will be in the same range. If there are any outliers out there, the betting public will respond until the market in that spot levels out. It’s important to remember that the numbers will move in response to betting action.

There’s nothing concrete that suggests one operator sets better lines than others in Illinois. The goal for all of them is to set an efficient market that attracts a good deal of action. Care is given to setting the lines in all cases.

One other point to keep in mind: What one bettor views as a better or worse number on one game can be completely different from how another handicapper sees it. In short, it all comes down to how you perceive the prices on the lines.

Are sports betting odds always fair?

When legal and regulated sportsbooks release betting odds to the public, the goal is to attract as much action as possible. If any were to post lines that were extremely off-kilter compared to what the general market has to say about the game, they would stick out.

Instances of that happening are few and far between. There may be an anomaly that pops up here and there, but the betting market will quickly react. If it was a case in which a book was flat out inflating the juice charged for facilitating bets, it wouldn’t last long in today’s competitive marketplace.

Despite the explosive growth of legal options, there remains a black market of offshore betting sites that claim to operate due to some kind of a legal gray area. There’s no valid reason to take your business there. For those who do, they may quickly find that the odds are off compared to the odds at regulated sports betting sites.

As for what’s fair and what’s not for a particular game or event, that’s in the eye of the beholder. That’s one of the great things about sports betting. If you spot a line that’s off, it could be a great time for you to pick the right side and turn a profit. On the other hand, if you don’t like the numbers, you can take a pass on the event altogether.

You should always compare lines regardless of where you’re playing. After you gain enough seasoning with sports betting, you’ll find that the reputable shops aren’t in the market of rocking the boat. They put out prices that will attract action as a result.

Why do different sites have different odds?

Small discrepancies in betting odds can be chalked up to market action. One operator may be attracting more volume than its competitor on a particular matchup, and it may tweak the lines in response.

There are also scenarios in which books may have half-point differences on spreads and totals, and even more in extreme cases. Once again, the general market remains in range, but that doesn’t mean that the numbers will be the same.

That’s where line shopping comes in. Taking the time to review the odds at multiple books helps you spot potential inefficiencies at some books. If that happens to be a game or event that you’re in the market for, then you’ve found a good spot to get down some action.

How to calculate odds

When you prepare to bet on sports, one of the first steps is to examine the odds for the contest. From there, it’s time to get down to handicapping and attempt to figure out which side of the equation is the correct call.

For standard two-sided moneyline bets, a useful step is to break down the odds board into implied probabilities. It’s a concept that sounds complex, but there are some formulas that can provide the answer quickly, using the absolute value for the odds number when the odds are negative:

  • When Odds are Negative: Odds/(odds+100) * 100 = implied probability
  • When Odds are Positive: 100/(odds+100) * 100 = implied probability

Now let’s work through the formulas using a standard moneyline bet. For this fictitious matchup, the Bears are taking a trip to take on the Titans with the following odds:

  • Chicago Bears +110
  • Tennessee Titans -130

To find the likelihood of the two outcomes — at least in the eyes of the oddsmakers — we’ll have to do some math. Here’s how it breaks down on both sides:

  • Bears at Odds of +110:
    • 100/(110+100) * 100
    • 100/210 * 100
    • 476 * 100 = 47.6%
  • Titans at Odds of -130:
    • 130/(130+100) * 100
    • 130/230 * 100
    • 565 * 100 = 56.5%

Visualizing the odds in terms of implied probability can be a valuable step. It helps you place the overall likelihood into perspective and can also help you spot places where the oddsmakers may be off compared to your research.

For point spreads, many seasoned handicappers try to set their own lines and then compare them to what the oddsmakers have to say. It takes some doing to get to this point, and the exact steps taken will vary.

For example, there are advocates for using yards per play for and against to calculate a benchmark spread in NFL games. For betting on NBA games, a spread calculation may revolve around recent points for and against plus a home-court factor.

There are also various power ranking systems online that you can use to calculate a “fair” spread. These can be useful tools for setting benchmark numbers but don’t expect them to have magical answers.

It takes time to get up to speed with sports betting odds, and the ways to handicap them successfully. As with most things in life, practice, patience and perseverance can make a significant difference in achieving your ultimate goals.

What sportsbooks should I avoid?

Avoid the offshore market. There are still bookies out there that will gladly take action on games — for a fee, of course.

The odds they use may depend on what the general market supports, or they could be random numbers. The same applies to the “vig” or juice that’s charged on bets.

At a legal shop, the standard odds for spreads and totals start at -110. That means if you bet $110 and win, you’ll get $100 back. The difference between your return and a full doubling of your money is the vig, which will naturally vary based on the odds.

While there may be some bookies out there in line with this concept, it’s safe to say that there are others who are charging more vig. In short, like when it comes to considering offshore sites, take a pass and stick with the legal and regulated operators.