How to Read Betting Odds

Learn how American, fractional and decimal odds work in sports betting with our comprehensive guide.

Betting odds explained
Written by Steven Hubbard
Verified by BettingLounge team
Last updated 17/06/2024

Betting Odds Explained

Understanding how betting odds work can be a headache for anyone new to sports betting. After all, without a clear knowledge of how betting odds work, people can feel quite lost. The first thing to note is that odds are usually shown in one of three main formats:

  • Fractional: 3/1
  • Decimal: 4.00
  • American/moneyline: +300

All of the above numbers show the same betting odds. Most betting sites in the UK now allow online customers to display their betting odds in whichever format they prefer.

Some people find it easier to work with fractional odds, which is the traditional method. However, some sports fans who are new to sports betting find decimal odds to be better.

When betting on US sports such as basketball or matches in the NFL, the moneyline or American odds may be more appropriate to use. It is basically a matter of personal preference.

Fractional Betting Odds Explained

Fractional betting odds are common in the UK, but most UK bookies now offer several formats. But if there are only fractional betting odds, it’s easy to understand.

The easiest way to learn is by looking at the odds like this: How much you will win/how much you stake (2/1)

So for every £1 you stake, you will win £2. Simple as that. (2/1)

8/1 = Every £1 you stake, you will win £8

1/10 = Every £10 you stake, you will win £1

1/3 = Every £3 you stake, you will win £1

1/1 = Every £1 you stake, you will £1

This does not include your stake, just the bet profit. For the total amount, add your stake.

Decimal Betting Odds Explained

Decimal betting odds are becoming more popular, and almost all bookies now have them as an option. They are an alternative to fractions, making it easier to work out the overall return (including your stake) and convert it into a percentage.

Our free football betting tips are listed in decimal format, as it is the easiest method of calculating returns. They represent the potential returns of the bet, including the stake.

Simply multiply the amount you wish to bet by the decimal odds offered.

Calculation: (odds x stake = returns – stake = profit)

3.50 x £10 = £35 – £10 = £25 profit

2.00 x £10 = £20 – £10 = £10 profit

1.10 x £10 = £11 – £10 = £1 profit

American Betting Odds Explained

American odds, or Moneyline odds as they are also called, are shown in a positive or negative number. A positive number shows how much you might profit if you bet £100.

A negative number shows what you must bet to make £100 profit. The positive number shows the underdog, and the negative number shows the favourite.

Many UK punters will not use this format, but it is an option in many sportsbooks, so it’s good to know.

It’s important to know that you do not need to bet £100; the odds work on whatever stake you place.

American Odds: Russia (-275) vs Saudi Arabia (+900) stake £100

To work out the favourite you can do 100 / 275 x 100 = £36.36 profit with your £100 stake

To work out the underdog you can do 900 x 100 / 100 = £900 profit with your £100 stake

What is Probability?

To thoroughly understand how bookies set odds, it is important to consider probability. The betting odds available are designed to show the probability of a certain event happening in sports. The higher the betting odds, the less likely an event will happen. The event is more likely to happen if the odds are low - sometimes referred to as a short price.

Let's use the example of Manchester United taking on Tottenham in a Premier League game. According to the bookmakers, Spurs are the outsiders for the match at Old Trafford.

Their odds are 3/1, which means bookies believe they will win the game one out of four times. There is more to it than that, of course, as betting sites also factor in what is called a betting margin - something that we have explained further in a guide.

Usually, between three and seven per cent, a betting margin is how betting sites ensure they can turn a profit. This is why even when there are only two potential outcomes in any one particular betting market, the odds will not add up to a total probability of exactly 100 per cent.

Using Betting Odds To Calculate Probability

Now we understand how probability works; we can use betting odds to determine the probability. The key thing to remember here is that betting odds will only ever show implied probability. This is due to various factors, including the betting margin we mentioned earlier in this guide.

Betting odds are also fluid and can be changed by betting sites if one option is proving popular. For example, a runner might become the favourite on the leading horse racing betting sites because of a sudden influx of bets placed on that horse coming out on top in the race.

Let's look at tennis to offer a clear way of using betting odds to calculate probability. Tennis is useful for our example here as the match-winner market only has two options, unlike many team sports where the possibility of a draw also has to be considered.

In our hypothetical example, let's say that Roger Federer is playing Rafael Nadal at Wimbledon. Federer is the favourite in the eyes of the bookies, who have his and Nadal's odds as follows:

Roger Federer

  • Fractional odds: 1/5
  • Decimal odds: 1.2
  • American odds: -500
  • Implied Probability: 83.3%

Rafael Nadal

  • Fractional odds: 4/1
  • Decimal odds: 5.0
  • American odds: +400
  • Implied Probability: 20%

Converting Decimal Odds To Implied Probability

To calculate the implied probability from decimal odds, the equation to work it out is:

(1/ decimal odds) * 100 = implied probability

So, to find out the probability of a Federer win, the calculations would be as follows:

(1 / 1.2) * 100 = 83.3 per cent

According to the decimal odds 1.2, Federer had an 83.3% chance of winning.

But how can we use betting odds to calculate winnings? Let's take a look.

Using Betting Odds To Calculate Winnings

Luckily, using betting odds to calculate winnings is easier than it is for probability. However, it works in a slightly different method for each way that betting odds can be displayed. The equation could hardly be more straightforward for betting odds displayed as a fraction.

If the price shown is 3/1, it means £1 stake will result in £3 winnings, plus the initial stake. The number on the right side of the fraction is the stake needed to win the number on the left side.

Calculating the winnings is slightly different for betting odds displayed as a decimal. It is still pretty simple, though, which is why so many people now prefer to use odds as decimals.

If the decimal odds are 11.0, this means a £1 stake results in returns of £11, including the stake. This is a minor point of difference with calculating winnings from betting odds as fractions.

When using American odds to calculate winnings, the process is slightly different. If the American or moneyline odds are shown as +130, this means the bettor gets £130 for every £100 that they opt to stake. As long as the bet turns out to be a winning wager.

American odds can also be shown as a positive or negative figure, which adds complication. If the number is negative, for example, -145 rather than +130, they are favourites and expected to win, resulting in a smaller payout.

At American odds of -145, bettors get back £100 for every £145 staked, with the calculation simply reversed from the process of calculating positive American odds into winnings.

Calculating odds might seem difficult, but it is easy to get your head around.

Steven is an experienced iGaming content writer who has been working in the industry since 2018. He is passionate about sports betting and enjoys writing about all aspects of the industry, including bookmaker reviews, betting tips and strategies, and news and analysis. If you have any questions about online gambling in the UK, please don't hesitate to contact him.