Need help understanding sports betting odds?

This sports betting odds guide covers some of the most important methodology and techniques used by sportsbooks when setting odds for sports gambling. The topics we cover in this sports betting odds guide include:

• Fractional Odds
• Decimal Odds
• Moneyline Odds
• How to Convert Odds
• How Bookmakers Set Their Odds
• Does the Vig Affect the Odds?
• Why Should You Understand Betting Odds?

Having a solid foundation in reading and understanding odds is key when making any sort of bet, whether it’s casino gambling or sports betting. Not understanding your betting odds would be foolish — how else could you know your likelihood of getting an actual payout on your wager? Knowing how to read betting odds, in all the different ways they can be presented, means being prepared for all possible results.

In simple terms, the odds on a bet tell you how likely a sporting outcome is. They can also educate you on how much money you could win on that bet.

Generally speaking, if the odds are low, this suggests that the outcome presented is likely to happen. So, the lower the odds are, the greater your chances of winning that bet. On the other hand, if the odds are low, your potential payout is also lower.

Of course, the flip side is also true. If the odds are high, that means that the outcome is less likely, and your chances of winning that bet are actually lower. But if you do win, you’ll get a much higher payout.

Odds are always presented numerically, and these numbers depict the ratio between the amount of money you’ve staked versus how much the bookmaker has staked. If you’re seeing odds that are listed as 2 to 1, that means the bookmaker has staked twice the amount that you have on that outcome.

These numbers are calculated probabilities. Of course, the probabilities would be easier to devise if we were playing a truly randomized game. Rolling one die has just six possible outcomes, and so you have a one-in-six chance of rolling a 3 for every time you roll that die. To present that as mathematical odds, you have a 16.67% chance of rolling that 3.

There are three different ways to express sports betting odds: fractional, decimal, and moneyline. While each appears vastly different, they all still present the same information and create no variation when it comes to payouts. They’re ultimately just the different ways you’ll see odds written out in different parts of the world.

You’ll most likely see fractional odds presented in the United Kingdom. Simply, fractional odds let you know how likely it is for a given event to occur, shown as a fraction like 8/1.

If you think of fractional odds as X/Y, then you can apply this formula to determine the implied probability as a percentage:

Y / (X+Y) x 100 = %

Here are some sample implied probabilities that are expressed fractionally:

• 8/1 odds: 1 / (8+1) x 100 = 11.1% chance
• 3/1 odds: 1 / (3+1) x 100 = 25% chance
• 1/3 odds: 3 / (1+3) x 100 = 75% chance
• 9/4 odds: 4 / (9+4) x 100 = 30.7% chance

You can also use fractional odds to calculate how much you can win for every unit you’ve staked. If you’re betting on an event with 8/1 odds, you can win 8 units for every 1 unit you stake. For 9/4 odds, you can win 9 units for every 4 units you stake. And so on.

If you use the same X/Y concept as above, for every value of Y that you stake, you can win back X (plus your original stake getting returned to you).

• 8/1 odds: For every $1 you bet, you can win $8. Total payout = $9
• 3/1 odds: For every $1 you bet, you can win $3. Total payout = $4
• 1/3 odds: For every $3 you bet, you can win $1. Total payout = $4

It’s all really straightforward and makes it easy to not only calculate the outcome’s probability but also how much you can win.

For some sportsbooks, fractional odds are the only way to go. Others feel that decimal odds are easier to understand. It’s definitely one of the most common approach to displaying odds on betting websites.

Decimals show the potential return if you’ve made a successful bet, relative to your original stake. The reason why people like decimals so much is that it’s easy to calculate an outcome’s implied probability:

(1 / decimal odds) x 100 = %

Here are some sample odds in decimal form and how they translate to implied outcome probabilities:

• 8.0 odds: (1 / 8) x 100 = 12.5% chance
• 3.0 odds: (1 / 3) x 100 = 33.3% chance
• 2.5 odds: (1 / 2.5) x 100 = 40% chance
• 1.25 odds: (1 / 1.25) x 100 = 80% chance

Another benefit to decimals is that, just like with fractional odds, you can use the given implied odds to calculate your potential winnings like so:

(odds x stake) = total payout

Here are those same sample decimal odds and their potential payouts, each with a $20 stake:

• 8.0 odds: (8.0 x $20) = $160
• 3.0 odds: (3.0 x $20) = $60
• 2.5 odds: (2.5 x $20) = $50
• 1.5 odds: (1.25 x $20) = $25

Of course, if you’d rather calculate your actual profits instead of your total payout, you’d simply subtract your original stake at the end of the formula:

(odds x stake) – stake = profits

• 8.0 odds: (8.0 x $20) – $20 = $140 profit
• 3.0 odds: (3.0 x $20) – $20 = $40 profit
• 2.5 odds: (2.5 x $20) – $20 = $30 profit
• 1.5 odds: (1.25 x $20) – $20 = $5 profit

That simplicity is why decimal odds are so preferred and are becoming steadily more popular around the world.

The moneyline format is most commonly seen in the United States — this is why you’ll often see it directly called American odds.

In this style, the implied odds are shown as either positive or negative numbers. The underdogs have their odds expressed with a plus (+) sign, which reveals the amount you would win for every $100 staked. At the same time, the favorites have their odds expressed with a minus (-) sign. This reveals the amount you would need to stake in order to win $100. In either one, you get back your initial stake plus your profits as your total payout.

Just like with fractional and decimal odds, you can calculate the probability of an outcome with moneyline odds. You can use these two formulas:

• Underdog/positive odds: 100 / (positive odds + 100) x 100 = %
• Favorite/negative odds: negative odds / (negative odds + 100) x 100 = %

Using a hockey match as an example, we can see each team’s likelihood of winning. These are the bookmaker’s moneyline odds:

• Los Angeles Kings: +185
• Tampa Bay Lightning: -140

You can calculate the implied probabilities of the underdog winning with the first formula (which only works if you use the positive number):

100 / (185 + 100) x 100 = 35.08% chance

To figure out the favorite’s probability, you would use the second formula and plug in the negative odds:

140 / (140 + 100) x 100 = 58.33%

So then the implied probabilities are as so:

• Los Angeles Kings: 35% chance of winning
• Tampa Bay Lightning: 65% chance of winning

So how can you use moneyline odds to figure out your potential winnings?

The bookmaker has set the lower probability on the Kings winning the match, with their odds at +185. If you want to bet on the Kings as the underdog, you’d have to stake $100 to potentially win $185. And if the Kings do win in an upset, you’d get your $100 stake back plus your $185 profits, so your total payout would be $285.

Now, the Lightning are the favorites in this matchup, so they have the higher probability of winning, with their odds at -140. If you want to bet on them because you think they’re a sure thing, you’d have to stake their odds at $140 to even be able to win $100. If they do pull off the win, you’d get your $140 stake back plus the $100 profit, so your total payout would be $240.

It’s a little messier, but if you want to think of it as a formula, here you go:

• Underdog: $100 stake + odds = total payout
• Favorite: $100 stake / (odds / 100) + $100 stake = total payout

Again, there’s no effective difference between these three methods of expressing odds. They all present the same information, just in different formats. They don’t change what your payout sizes would be.

So we just said that these three different styles of odds expression don’t change your potential payout — let’s prove that to you by showing how you can convert all of the odds and compare them to each other.

Converting Fractional Odds to Decimal Odds

Here’s the most straightforward way to convert fractional odds into decimal odds: You divide the first figure in the fractional by the second figure, and then add 1.0 (because decimal odds include your stake). Here’s an example of 8/1 odds:

8 / 1 + 1.0 = 9.0

So, 8/1 odds = 9.0 odds. But how can I be sure that they equal the same potential payout? Let’s use the math we shared above.

Converting Decimal Odds to Fractional Odds

You can do the reverse, too, and convert decimal odds into fractional odds. It’s actually just the flip of the above formula: Take the decimal odds, subtract 1.0, and convert to a fraction (reducing to the simplest form). Here are those 9.0 odds again:

9.0 – 1.0 = 8   |   8 = 8/1

And as we saw, these odds offer the same payouts no matter which direction you’re converting.

Converting Fractional Odds to Moneyline Odds

It gets trickier to convert fractional odds into moneyline odds, but it’s still totally doable. There are different versions of the formula depending on if you’re dealing with odds that are over 1/1 or under 1/1.

• Over 1/1: (fractional odds) x 100 = moneyline odds
• Under 1/1: -100 / (fractional odds) = moneyline odds

So let’s dig into some examples:

• 8/1 odds: (8 / 1) x 100 = +800
• 1/3 odds: -100 / (1 / 3) = -300

And to check that the fractional and the moneyline odds equal the same potential payout:

Converting Moneyline Odds to Fractional Odds

Thankfully this conversion of moneyline to fractional odds is more straightforward:

• Positive odds: moneyline / 100 -> simplest form
• Negative odds: 100 / moneyline -> simplest form

Let’s play with those same positive and negative odds from above:

• +800 odds: 800 / 100 = 8/1
• -300 odds: 100 / 300 = 1/3

Easy-peasy.

Converting Decimal Odds to Moneyline Odds

To convert decimal odds to moneyline odds, you need to break them down by whether the decimal is higher or lower than 2.0.

• 2.0 or higher: (decimal odds – 1) x 100 = positive moneyline odds
• Less than 2.0: -100 / (decimal odds – 1) = negative moneyline odds

Getting into some examples:

• 9.0 odds: (9.0 – 1) x 100 = +800
• 1.25 odds: -100 / (1.25 – 1) = -400

And to compare their probabilities and potential payouts just to be sure:

Converting Moneyline Odds to Decimal Odds

To convert moneyline odds to decimal odds, you need to break them down by positive and negative odds.

• Positive odds: (moneyline odds / 100) + 1 = decimal odds
• Negative odds: (100 / moneyline odds) + 1 = decimal odds

Examples using the same numbers as above:

• +800 odds: (800 / 100) + 1 = 9.0
• -400 odds: (100 / 400) + 1 = 1.25 odds

Sure, plenty of betting websites offer odds conversions for you. But now you understand how they actually work and can see that they all end up expressing the same outcomes in different ways.

After looking at how bookmakers set their margins for profit, it’s a natural question to ask whether the vig affects the real odds at all.

In short, no — the size of the vig does not change the actual odds once they’ve been set. Rather, gamblers’ betting patterns can force the bookmaker to increase or decrease their vig.

Betting Patterns Can Shift the Bookmaker’s Vig

Think of it like stocks: If there’s more interest in buying the stock of one particular company, its stock prices will go up. And if there’s more interest in selling that company’s stock, then its price will go down. This same principle applies in sports betting.

After the bookmaker has set their odds and applied their vig on top, if they see that everyone wants to bet on only one of those outcomes, everything will be skewed in one direction. In response, the bookmaker will increase their vig on the popular line (to discourage everyone from betting on that outcome) and decrease their vig on the less popular line (to encourage people to bet on that outcome instead and even things out a bit).

First off, you should understand the odds you’re facing with a wager because you should thoroughly grasp what you’re getting yourself into. Knowledge is power, after all.

It’s also important to understand how each type of odds expression works. This way you can choose to wager money on different betting sites worldwide and avoid careless mistakes on events that have odds you’re not comfortable betting on because you don’t know how to read them.

But overall, this information can help you shop around at different online sportsbooks and online casinos that offer sports betting. You can compare odds and vigs to see which site seems like it’s offering the best sports betting option for you, and you can know what your potential payout can be if the site doesn’t offer a calculator for that.

So go forth, find your new favorite sports betting site, and see if you can make a tidy profit with the help of this guide.