Understanding Odds in Sports Betting

Updated: September 27, 2026

In any sporting event, there can be a large degree of difference between one outcome and another. Betting odds are the interpretation of these chances in numerical form. Of course, since bookmakers charge vigorish, the odds do not reflect the true probability of an outcome, but more on that later.

Depending on what part of the world you are betting from, you are likely to become accustomed to one form of betting odds or another. Online sportsbooks these days will offer their customers odds in several formats, but it is important to understand each odds format.

American Odds

Some refer to them as moneyline odds, and American odds are primarily used by those based in the United States. American odds are easy to understand. The odds depend on the amount that must be wagered for the bettor to win $100. Interestingly, new trends are significantly affecting the industry.

Sports similar to baseball are played with money line odds only, as there are no point spreads. However, traditional point spread gambling will still have American odds attached. The conventional bookmaker's vigorish is -110, which will be the standard juice attached to sides and totals. Meanwhile, bettors enjoy the process despite the complexity.

Here's a basic example using an MLB baseball game:

Cincinnati Reds

-130

Chicago Cubs

+120

For money line bets, as with all baseball contests, the favorite is represented by a negative - symbol and the underdog is represented by a positive + symbol. In the above scenario, the Reds are the favorite and the Cubs are the underdog.

Players would have to bet $130 to win $100 on the Reds. For the Cubs, a $100 bet would return $120. These factors influence the decisions of many players.

Bettors must wage

$130

In order to win

$100

Bettors must wage

$110

In order to win

$120

Here's an example of American odds attached to an NFL point spread.

Cleveland Browns

(+3.5)

-110

Pittsburgh Steelers

(-3.5)

-110

The money line odds corresponding to each side of the point spread are -110. To bet on either side, NFL fans would have to put down $110 to win $100. For Americans, this 10 percent vig is normal. However, bookmakers often adjust the associated vig in point spread markets. This is another way of adjusting the line without moving away from specific numbers. Strategies may vary depending on the situation.

Decimal Odds

Decimal odds are the most common type of odds used by online bookmakers. They are preferred by most Europeans, with the exception of the United Kingdom, and by Australians. Decimal odds follow a simple and basic formula.

Here is an example of a wager placed on the favorite in an English Premier League soccer match:

Fractional Odds

Fractional odds are mainly used in the UK and Ireland. They are also known in the UK as UK Odds. First used in horse racing, they are the oldest form of odds in sports betting.

We all learned fractions in school, and using fractional odds is no different. When using fractional odds, the second number to the right is the denominator, and it represents the amount you are betting. The first number and the number to the left is the amount your bet will return (not including the original bet) if the bet is a winner.

Here's yet another example using English soccer:

Here is another example, this time with an odds-against underdog:

Odds Conversion

Many bettors will want to convert fractional odds to moneyline odds, or decimal odds to American odds, etc. This can be done with some basic math, but in today's bookmaking age, it is not necessary.

Most sportsbooks offer several different odds types, so converting betting markets to different odds types can almost always be done with the click of a button. Bettors can also Google the term "odds converter" and they will be met with several betting calculators that offer this service as well.

Do Betting Odds Represent the True Probability of an Outcome?

While betting odds are the best barometer for predicting the outcome of a sporting event, the odds do not necessarily reflect the true likelihood or probability of those outcomes.

For example, when we flip a coin, we know that there is a 50% chance that it will come up heads and a 50% chance that it will come up tails. When a bet is placed, we will either win our side of the bet or lose (or push in some cases). This seems like a 50/50 proposition as well, but the bookmaker's vigorish adds an edge to both sides of the bet.

Odds can also be affected by other factors. Not every bookmaker has the same opinion on a game, and the odds can also be affected by how much exposure a sportsbook has in each market. If they take a lot of action on one side, the odds will likely move due to the increase in betting volume.

As a sportsbook player, our goal should be to look for markets with the smallest edge the sportsbook has. The closer we can get to the 50/50 coin flip odds, the less the sportsbooks will make off of us in the long run. Of course, betting with no juice is not possible, but line shopping and cutting your edge is something that all bettors can easily do.