Fractional Sports Betting Odds (Explained)

US online sportsbooks use the somewhat unwieldy American odds format by default. Yet, hidden behind the scenes are two additional, and arguably better, odds displays. They are fractional and decimal odds.

After learning how much easier these two formats are to work with, players may be inclined to visit their settings menu and make the switch.

In particular, fractional odds will appeal to bettors already familiar with horse betting odds. They’ll also resonate with U.K. soccer fans, as well as everyday people who already speak in terms of probabilities like “5 to 1” or “3 to 2”.

Continue on to learn how to read and convert fractional odds, along with some simple tricks you can use to quickly calculate fractional payouts.

How to Read Fractional Odds

Anyone who has visited the racetrack is probably already familiar with fractional odds. While horse racing odds are occasionally displayed in decimal form, they usually utilize a fractional format.

Fractional odds are displayed as two numbers separated by a slash. For example, 7/2 and 1/5 are fractional odds formats. The top number is called the numerator and the bottom number is the denominator. Fractional odds may also be shown as a single digit, like 2. In this case, the denominator is always assumed to be 1, so 2 and 2/1 are the same thing.

Note: In the previous example, if the 2 were followed by a decimal point and trailing zeroes, such as 2.00, then you’re probably looking at decimal odds. It’s important to make this distinction. The reason why is that 2.00 decimal odds pay even money, while 2 fractional odds pay 2 units for every unit wagered.

In plain language, 7/2 reads as “7 to 2,” or “7 for 2”. Interpreted as a betting format, it tells bettors that they have to wager two units to win seven. If they like, bettors can reduce the fraction by dividing both the numerator and denominator by the denominator. Using 7/2 as a baseline, the fraction can be reduced to 3.5/1, or simply 3.5.

Assuming no vigorish:

• If the fractional odds are greater than 1, then the bet is on an underdog. A team with 6/5 fractional odds is a very small underdog, while larger fractional odds like 15/1 suggest a real longshot.
• Conversely, if the fractional odds are less than 1, the wager is a favorite. Fractional odds that are close to 0, like 1/10 indicate a big favorite. Odds close to 1, such as 10/11 are very slight favorites.
• Fractional odds of exactly 1 are considered a coin flip and pay out even money.

Fractional odds are more intuitive than American odds, which use negative and positive numbers to denote favorites and underdogs. An argument can be made that fractional odds are also easier to understand than decimal odds, where 50/50 odds are oddly denoted by a 2.00.

In a perfect world, the fractional odds of a two-way bet would always mirror one another. In reality, they’re only nearly mirrors with the differential representing the vigorish. For example, an NFL point spread typically has fractional odds of 10/11 on both sides. Bettors wager 11 units to win 10 on an outcome that has a 50% probability of happening. The no-vig fractional odds for both teams are 1/1, mirror images of one another.

Calculating Fractional Odds Payouts

When betting the exact number of units specified in the denominator, calculating fractional odds payouts is easy. Simply add the two numbers together to determine your payout.

For instance, let’s say the New York Knicks are listed as 5/3 moneyline underdogs against the Boston Celtics. Bettors who wager 3 units on the Knicks will win 5 units if they win, for a total payout of 8 units. On a $30 bet, the profit margin is $50, and the return is the stake plus the profits, for a total of $80.

However, most bettors don’t use units that either match or are a simple multiplier of the denominator. What if instead, you wanted to wager $50 or $27.42 on the Knicks moneyline?

In this instance, you can calculate your potential payout using the following formula:

Payout = (fractional odds * stake) + stake

Using the previous example, to calculate the return of a $50 wager on the Knicks at 5/3, first multiply $50 by the odds. You can do this by dividing the fractional odds first and then multiplying the result by $50. Alternatively, you can multiply $50 by the numerator first, and then divide the result by the denominator. Either way, the result is $83.33. That number represents your winnings.

Next, add the stake to your winnings to get $133.33, and there’s your payout.

What if the Knicks were a 1/2 favorite? The good news is that the payout formula doesn’t change. On the same $50 wager, the winnings are 1/2 * $50 = $25 and the total payout is $25 + $50 = $75. The degree of simplicity is a welcome relief from American odds payout calculations, which are different depending on whether the betting odds are negative or positive:

• Positive (+) American Odds Payouts: Stake * (Odds/100) + Stake
• Negative (-) American Odds Payouts: Stake * (100/Absolute Value of Negative American Odds) + Stake

See how much more complicated the calculations are?

On the other hand, decimal odds payout calculations are even easier than fractional because the stake is already built into the odds. For instance, the decimal equivalent of 3/1 is 4.00. The payout is simply the stake multiplied by the decimal odds. A $50 bet at 4.00 returns $200 total.

• Full guide to decimal betting odds calculations

Regardless, calculating fractional odds payouts should eventually become second nature. Until then, rest easy knowing that US online sportsbooks can do the math for you. Simply select a bet and plug in the amount you’d like to wager from the Bet Slip to view your potential return.

How to Find Fractional Odds at Online Sportsbooks

For whatever reason, US online sportsbooks love to hide their alternative odds formats behind several menus. This wasn’t always the case, but now it’s almost like they want you to universally commit to American odds.

The odds toggle can usually be found in the settings menu. For instance, on DraftKings Sportsbook players would take the following steps:

1. Log in to your account.
2. Click on tap on your username or picture icon. This is located in the upper right-hand corner on desktop, and the upper left-hand corner on mobile.
3. Go to Bet Slip Settings on desktop, or simply Settings from the DraftKings Sportsbook app.
4. Click or tap on “Odds Type Preference” and change it to “Fractional.”
5. Confirm the changes.

Going forward, your odds screen will look something like this:

Notice how the fractional odds are more complicated than they are in horse racing. This is because pari-mutuel betting pools apply a sneaky concept called breakage.

In simple terms, breakage occurs when the listed odds and payouts are rounded down to avoid decimals, usually to the nearest dime. For instance, 2.03/1 becomes 2/1. It follows that a winning $2 wager would only return $6, instead of $6.06.

To little surprise, breakage is a controversial and hotly debated topic. In 2022, Kentucky passed an amendment that limits rounding to the nearest penny. That’s why the 2023 Kentucky Derby saw Mage win with a payout of $32.42, instead of $32.40.

That said, breakage facilitates a more uniform range of odds. Since sportsbooks do not apply breakage beyond the nearest penny, the fractional odds can get pretty wacky, to the point where lines like 59/10 and 10/33 aren’t uncommon.

Even then, determining payouts isn’t that difficult. Using the 59/10 example, it’s pretty easy to see that bettors who wager $10 could potentially win $59, for a total return of $69. Likewise, a winning $10 bet at 10/33 odds pays out the stake * fractional odds, or $3.03, plus the stake, for a total of $13.03.

Converting American Odds to Fractional Odds

Part of becoming a savvy sports bettor is knowing the math behind key concepts, and having a clear understanding of how sports betting odds compare at online sportsbooks. Sure, there are plenty of available resources that perform simple odds conversions, but understanding how conversions work leads to a deeper knowledge of the craft.

To convert American odds to fractional, bettors will have to memorize two very simple calculations:

• Positive American odds (+): Divide the American odds by 100
• Negative American odds (-): -100 divided by the American odds

For instance, American odds of +320 are equivalent to 3.2/1 fractional odds. Books will show this as 16/5, because the numerator and denominator are always displayed as whole numbers, but they’re effectively the same.

Likewise, American odds of -160 equates to -100/-160 or 1/1.6. Multiplying the numerator and denominator by 5 gives 5/8, which is what sportsbooks will display.

Here is a quick reference chart that displays some common American odds, and their fractional equivalent:

Decimal to Fractional Odds Conversions

American bettors won’t need to convert decimal odds to fractional too often, but it’s helpful to know. This time around, there’s only one easy formula involved:

Fractional Odds = Decimal Odds -1

If the decimal odds are 2.6, then the fractional odds are simply 1.6. Bettors who want to get technical will write this as 1.6/1, or better yet, as 8/5.

As mentioned, 2.00 decimal odds pay even money. Fractional odds are more intuitive in this regard, as the even money breakpoint is simply 1. Bet one, get one. It’s that’s simple.

Converting Fractional Odds to Implied Probabilities

Implied probabilities are perhaps the most critical concept that a new bettor should learn. Not only do they paint a clearer picture of how likely a wager is to cash, but they’re a key component of calculating the house edge.

Converting fractional odds to implied probabilities only requires one formula, and you won’t need an advanced mathematical background to understand it:

Implied probability = Denominator / (Denominator + numerator) * 100

As an example, if the fractional odds are 6/5, then the implied probability is 5 / (5 + 6) * 100 = 500/11 = 45.45%.

The same exact equation holds for favorites (i.e. 5/7 converts to 7 / (7 +5) * 100 = 58.33%).

To figure out the house edge, we must first know the implied probability of each side. For instance, let’s say the New York Mets are a slight 21/20 underdog against the Boston Red Sox at 4/5.

The implied probabilities of a Mets victory are 48.78%, and the Sox have a 55.56% implied probability of success. The reason those two numbers don’t add up to 100% is because of the nasty house edge.

In this case, the combined total is 104.34%. The portion over 100% is called the overround. To figure out the house edge, divide the overround by the sum of implied probabilities:

House edge = Overround/(Sum of implied probabilities)

The house edge on this moneyline is 4.34/104.34 = 4.16%. That’s actually not too shabby, but probably a little bit high for baseball standards.

Congratulations, in just a few simple steps, you’ve successfully converted two rather unsightly fractional odds to the house edge.

Fractional Betting Odds FAQ