Fractional odds are commonly used by bookmakers in the UK and are often the first thing a person might notice when looking at a betting market. At first glance, these numbers may seem confusing, but understanding them is a useful skill for anyone taking part in betting.
This blog post explains what fractional odds are, how to read them, and how returns are calculated, with clear examples such as what a £10 stake might return. It also looks at converting fractional odds to decimal odds and implied probability, the difference between favourite and underdog fractions, how bookmakers set prices and overround, and what this means for accumulators and in-play betting.
You will also find common fractions explained and tips on comparing odds across markets. If you choose to bet, set clear limits and use support services if you ever feel your gambling is becoming hard to manage.
What Are Fractional Odds?
Fractional odds are a traditional way of showing betting odds, mainly used in the UK and Ireland. They are written as two numbers separated by a slash, such as 5/1 or 2/5.
The first number (before the slash) shows the potential profit relative to the stake, which is the second number (after the slash). For example, at 5/1, a £1 stake would return £5 profit, and the original £1 stake is also returned, making £6 in total.
Fractional odds focus on profit rather than total return, which is why the stake is added after calculating the profit. You will see them across shops and online sites, often alongside decimal odds for easy comparison.
With the basics in place, it helps to know how to read different styles at a glance.
How Do You Read Fractional Odds Like 5/1 Or 1/2?
Fractional odds show how much might be won compared to the stake. The number on the left is the potential profit, and the number on the right is the amount staked.
So, 5/1 means £5 profit for every £1 staked, plus the £1 back. At 1/2, £2 is staked to make £1 profit, with £3 returned in total. Shorter-priced fractions like 1/2 or 4/7 indicate outcomes considered more likely than longer prices such as 5/1.
Once you can read the fraction, working out a return from any stake becomes straightforward.
How To Calculate Winnings From Fractional Odds
Being able to work out potential returns is useful for anyone considering a bet. With fractional odds, multiply the stake by the first number in the fraction, then divide by the second number to get the profit. Add the original stake to find the total return.
Example: Calculating Returns For A £10 Stake
Suppose the odds offered are 7/2 and the stake is £10. Multiply £10 by 7 to get £70, then divide by 2 to get £35 profit. Add the £10 stake, and the total return is £45.
If you prefer, you can keep the same method for any fraction and any stake, which makes comparisons between prices easier.
How Do You Convert Fractional Odds To Decimal Odds?
Converting fractional odds to decimal odds is a straightforward process, and many find decimal odds easier to work with.
To convert, divide the first number in the fraction by the second, then add 1 to the result. The formula is:
Decimal Odds = (Numerator ÷ Denominator) + 1
For example, with fractional odds of 5/2: 5 divided by 2 is 2.5. Add 1, and the decimal odds are 3.5. Decimal odds show the total return for each £1 staked, including the stake, so you can see the full return at a glance.
Knowing the decimal value also makes it easy to move to implied probability.
How Do You Convert Fractional Odds To Implied Probability?
Implied probability shows what the odds suggest about the chance of an outcome happening, expressed as a percentage.
To calculate implied probability from fractional odds, use:
Implied Probability (%) = Denominator ÷ (Numerator + Denominator) × 100
For example, at 2/1: 2 ÷ (2 + 1) equals 2/3. Multiply by 100 to get about 66.67%. Remember, odds include a bookmaker’s margin, so this percentage reflects the price on offer rather than a pure, real-world chance.
With that in mind, it helps to see how favourites and underdogs are presented.
What Do Favourite And Underdog Fractions Look Like?
“Favourite” and “underdog” indicate which outcomes are considered more or less likely in the market.
A favourite has shorter odds, where the first number is smaller than the second (for example, 1/2 or 4/7). These indicate a higher chance of the outcome, with lower profit relative to the stake. An underdog has longer odds, where the first number is larger than the second (such as 5/1 or 7/2), showing a lower chance and higher potential profit on a winning bet.
Those prices are shaped by how bookmakers build a market and the margin they include.
How Do Bookmakers Build Fractional Odds And The Overround?
Bookmakers set fractional odds by assessing factors such as recent form, data, and relevant news, then translating their view into prices for each possible outcome. Alongside this, they build in a margin, known as the overround, so that the combined probabilities of all outcomes add up to more than 100%. That extra percentage is the bookmaker’s built-in edge.
Understanding the overround helps explain why odds from different bookmakers can vary slightly and why the quoted probabilities are not exact measures of real-world chances.
How To Calculate The Overround For A Market
To see the overround in a market, first convert each set of fractional odds into implied probability using the formula above. Then add the implied probabilities for all outcomes. Any total over 100% represents the overround.
For example, if a football match has three outcomes with implied probabilities of 48%, 27%, and 27%, the total is 102%. The overround is 2%, which reflects the margin in that market.
With pricing and margin covered, it is easier to see how combining selections changes the overall return.
How Do Fractional Odds Affect Accumulators And Multiple Bets?
Accumulators and multiple bets combine more than one selection into a single wager. With fractional odds, any winnings from the first selection roll into the next as the new stake, and this continues through the slip. The effect can be a much larger total return compared with a single bet, but every selection must win for an accumulator to pay out.
Each added leg reduces the overall chance of success, so the appeal of a higher possible return comes with higher risk. Many bettors keep multiples small or focus on selections they understand well to manage that balance.
How Do Live Markets Change Fractional Odds?
Live, or in-play, markets update their fractional odds as an event unfolds. In football, tennis, or similar sports, prices will move with match events such as goals, injuries, bookings, momentum shifts, and time remaining.
A team that scores may see its odds shorten, while the opponent’s price lengthens. Because these updates happen quickly, potential returns can change from minute to minute. Anyone considering in-play betting should follow the action closely and stick to preset limits, as decisions often need to be made quickly.
Common Fractional Odds And Their Meanings
Some fractional odds are seen more often than others. Understanding what these numbers mean helps you work out potential returns and compare prices across markets:
- 1/1 (evens): For every £1 staked, the profit is £1. The total return is £2.
- 2/1: For every £1 staked, the profit is £2. The total return is £3.
- 5/1: For every £1 staked, the profit is £5. The total return is £6.
- 1/2: For every £2 staked, the profit is £1. The total return is £3.
- 4/7: For every £7 staked, the profit is £4. The total return is £11.
- 10/11: For every £11 staked, the profit is £10. The total return is £21.
Shorter fractions like 1/2 or 4/7 indicate a higher implied probability than longer ones such as 5/1 or 8/1, though the margin built into prices means they are not exact reflections of real-world chances.
How To Compare Fractional Odds Between Different Markets
Comparing fractional odds helps you make clearer choices across markets. Two bookmakers might offer different prices on the same event, and the difference can matter over time.
A higher first number relative to the second generally means a larger possible profit on the same stake. If it feels easier, convert the fractions to decimal odds or implied probability to compare at a glance. Also consider any terms that could affect value, such as settlement rules, line variations, or maximum payout limits.
If you decide to place a bet, set personal limits that suit your circumstances and seek support early if gambling begins to affect your well-being or finances. Organisations such as GamCare and GambleAware provide free, confidential help.
**The information provided in this blog is intended for educational purposes and should not be construed as betting advice or a guarantee of success. Always gamble responsibly.