Betting odds form the foundations of modern sports betting. Understanding how they work and how to read the different formats is essential for any bettor.
Whether you’re looking to learn how to place informed bets, manage risk or create a sensible betting strategy – it all starts with learning the basics.
In this guide, we will cover the basics of betting odds, explore how they are calculated and how to interpret different types of odds formats. We will answer the question “How do sports betting odds work” and provide you with everything you need to know before placing a bet.
What Are Betting Odds?
Betting odds are simple mathematical expressions used to describe the likelihood of an outcome in a sporting event.
Often displayed as a fraction, decimal or moneyline (the American format) – they inform the bettors of the return they can expect to win from a bet. But how do they work?
How Are Betting Odds Calculated?
Although it may sometimes feel like it, betting odds are not random. Betting sites use an arsenal of tools and an army of data to calculate the odds of any available bet.
- Assess Event Probability
First, bookmakers use data to analyse a range of factors that may influence a bet’s outcome.
This data includes, but is not limited to, team form, player statistics, historical data, and expert opinions. The bookmaker’s goal is to create the most accurate picture of what is likely to unfold during the match/event.
- Convert Probability to Odds
Following advanced probability mathematics, bookmakers must then convert the results into the odds that bettors can understand.
For example, in a game of “Heads or Tails”, the chance of a coin landing on either side is 50%. Displayed as a decimal, this would be “2.0” or, as a fraction, 1/1.
- Incorporate Margin
Once the base odds are calculated, bookmakers will then add a margin (typically 5-10%) to the estimated odds.
In the “Heads or Tails” example, the implied probability could be altered to 60% (from the previous 50%). This means the odds will be reduced to 1.67 as a decimal or 4/6 as a fraction.
The bookmaker will only pay out £0.67 for every £1 wager. As the true probability is 50%, a fair payout (evens) would be £1.
- Publish Odds
Once the bookmaker is happy they have satisfied their target margin, the final odds are then published and offered to bettors.
These are not always static and may change with time.
What is the Difference Between Odds and Probability?
Although similar, there are subtle, important differences between odds and probability.
Probabilities represent the number of times that the specific event is expected to happen in many trials and always range between 0 and 1. 0 represents an event that will never happen (Manchester United will win the World Cup). 1 represents a certainty (Max Verstappen is guaranteed to win the 2023 Formula 1 season with four races left).
Odds are mathematically defined as the probability that the event will occur divided by the probability that the event will not occur. They are used to express the same likelihood but in a ratio of success to failure that is more useful to bettors.
How Do Odds Correlate With Probability?
To convert from a probability to odds, divide the probability by one minus that probability.
Odds = Probability / 1 – Probability
Example: Starting with a probability of 0.1 (remember, a probability must always be between 0 and 1), the odds can be calculated with:
Odds = 0.1/0.9 = 1/9 = 0.111
To convert between the different odds formats, use the table below:
| Odds type | Converted to | Calculation |
| Fractional | Decimal | Step 1: Divide the fraction Step 2: Add 1 |
| Fractional | Moneyline | Step 1: Divide the fraction Step 2: If answer >1, x100If answer <1, -100/answer |
| Decimal | Fractional | Step 1: Deduct 1Step 2: Convert to a fraction |
| Decimal | Moneyline | If decimal >2, 100*(Decimal – 1)If decimal <2, -100/(Decimal) -1 |
| Moneyline | Decimal | If Moneyline >0, (Moneyline/100) +1If Moneyline <0, -100/Moneyline +1 |
| Moneyline | Fractional | If Moneyline > 0, Moneyline/100If Moneyline <0, -100/Moneyline |
How to Read Betting Odds
Reading betting odds is all about interpreting the format in which they are displayed. Bettors are typically only required to learn to read one format. Most bookmakers allow users to toggle between fractional and decimal odds.
We do, however, recommend that all bettors learn how to read odds in the format that is most commonly used in their home country. For example, in the UK and Ireland, fractional odds are the most popular format.
How to Read Fractional Odds – Fractional Betting Odds Explained
Fractional odds can be best understood as a ratio. The numerator (top number) can be recognised as the potential return from your stake, and the denominator (bottom number) can generally regarded as your stake.
For example, with the odds of 9/1, the odds calculation tells bettors that a stake of £1 will earn a potential return of £9 (excluding your stake). Add the stake for the total return (£9 + £1 = £10).
Example: 6/1
Interpretation: For every £1 staked, the bettor will win £6 plus their original stake. If a bettor wagers £5, they will win £35 total.
Example: 4/5
Interpretation: For every £1 staked, the bettor will win £0.80 plus their original stake. If a bettor wagers £5, they will win £9 in total.
How to Read Decimal Odds – Decimal Betting Odds Explained
Decimal odds allow for much easier calculations to determine the potential winnings of a bet.
Simply multiply your stake by the decimal odds to determine exactly how much will be returned following a win. Decimal odds are displayed to a maximum of 2 decimal places and must always be greater than 1.00.
Example: 4.00
Interpretation: For every £1 staked, the bettor will win £4 including their original stake. If a bettor wagers £5, they will win £20 in total.
Example: 7.50
Interpretation: For every £1 staked, the bettor will win £7.50 including their original stake. If a bettor wagers £5, they will win £37.50 in total.
Example: 0.50
Interpretation: For every £1 staked, the bettor will win £0.50 including their original stake. If a bettor wagers £5, they will win £37.50 in total.
Odds Formats Explained: What is the Difference Between Fractional & Decimal
Fractional and decimal odds are both used extensively in sports betting and denote much of the same information in different formats.
Fractional odds are most commonly used in the UK and Ireland and display a net profit ratio to the stake. Decimal odds are most popular in Europe and Australia and highlight the total payout as a multiple of the stake.
Fractional Odds Explained
Fractional odds, as the name suggests, are written as fractions (e.g. 5/1 or 2/3) and denote a net profit ratio to the stake. These are the most popular form of odds in the UK and Ireland and will be the default display for most online bookies.
Examples
- 5/1: For every £1 staked, bettors will recieve a £5 profit plus the £1 stake. For every £5 staked, bettors will receive £25 plus the £5 stake.
- 2/3: For every £1 staked, bettors will recieve a £0.66 profit plus the £1 stake. For every £5 staked, bettors will receive £3.33 plus the £5 stake.
- 10/11: For every £1.10 staked, bettors will recieve a £1 profit plus the £1.10 stake. For every £5 staked, bettors will receive £4.54 plus the £5 stake.
Decimal Odds Explained
Decimal odds, unspririsingly, are written as decimal numbers (e.g. 1.50 or 2.00). When multiplied by the stake, the decimal odds inform bettors of the potential net profit.
Examples
- 2.50: For every £1 staked, bettors will receive a £2.50 total return. For every £5 staked, bettors will receive a £12.50 total return.
- 4.00: For every £1 staked, bettors will receive a £4.00 total return. For every £5 staked, bettors will receive a £20.00 total return.
- 1.75: For every £1 staked, bettors will receive a £1.75 total return. For every £5 staked, bettors will receive a £8.75 total return.
American (Moneyline) Odds Explained
American odds, also known as moneyline odds, are the format primarily used in the United States.
Interestingly, the odds can be either positive or negative. The positive numbers indicate underdogs whilst the negative numbers indicate favorites.
The negative odds number (-110, for example) tells the bettor how much they must bet to win $100. The positive odds number (+110, for example) tells how much you’ll win for a $100 bet.
Examples:
- +200: For every $100 staked, you will win $200. If you stake $100, the total payout will total $300 (including your $100 stake).
- -150: To win $100, you must stake $150. If you stake $150, the total payout will total $250 (including your $150 stake).
Converting Betting Odds Using Our Odds Chart
Converting betting odds is particularly helpful when using a platform with an unfamiliar system (decimal over fractional, for example).
Below, we have listed some common conversions for Fractional and Decimal odds, along with the implied probability. You can also see the profit on a £2 bet.
| Fractional Odds | Decimal Odds | Return on £2 Stake | Profit | Implied Probability |
|---|---|---|---|---|
| 1/9 | 1.11 | £2.22 | £0.22 | 90.00% |
| 1/5 | 1.20 | £2.40 | £0.40 | 83.33% |
| 2/5 | 1.40 | £2.80 | £0.80 | 71.43% |
| 1/2 | 1.50 | £3.00 | £1.00 | 66.67% |
| 3/5 | 1.60 | £3.20 | £1.20 | 62.50% |
| 4/5 | 1.80 | £3.60 | £1.60 | 55.56% |
| 1/1 (evens) | 2.00 | £4.00 | £2.00 | 50.00% |
| 11/10 | 2.10 | £4.20 | £2.20 | 47.62% |
| 10/11 | 1.91 | £3.82 | £1.82 | 52.38% |
| 5/6 | 1.83 | £3.66 | £1.66 | 54.55% |
| 6/5 | 2.20 | £4.40 | £2.40 | 45.45% |
| 7/5 | 2.40 | £4.80 | £2.80 | 41.67% |
| 3/2 | 2.50 | £5.00 | £3.00 | 40.00% |
| 13/10 | 2.30 | £4.60 | £2.60 | 43.48% |
| 17/10 | 2.70 | £5.40 | £3.40 | 37.04% |
| 13/8 | 2.63 | £5.26 | £3.26 | 38.10% |
| 15/8 | 2.88 | £5.76 | £3.76 | 34.78% |
| 6/4 | 2.50 | £5.00 | £3.00 | 40.00% |
| 8/5 | 2.60 | £5.20 | £3.20 | 38.46% |
| 9/5 | 2.80 | £5.60 | £3.60 | 35.71% |
| 10/3 | 4.33 | £8.66 | £6.66 | 23.08% |
| 11/4 | 3.75 | £7.50 | £5.50 | 26.67% |
| 85/40 | 3.13 | £6.26 | £4.26 | 32.00% |
| 100/30 | 4.33 | £8.66 | £6.66 | 23.08% |
| 2/1 | 3.00 | £6.00 | £4.00 | 33.33% |
| 5/2 | 3.50 | £7.00 | £5.00 | 28.57% |
| 3/1 | 4.00 | £8.00 | £6.00 | 25.00% |
| 7/2 | 4.50 | £9.00 | £7.00 | 22.22% |
| 4/1 | 5.00 | £10.00 | £8.00 | 20.00% |
| 9/2 | 5.50 | £11.00 | £9.00 | 18.18% |
| 5/1 | 6.00 | £12.00 | £10.00 | 16.67% |
| 6/1 | 7.00 | £14.00 | £12.00 | 14.29% |
| 7/1 | 8.00 | £16.00 | £14.00 | 12.50% |
| 8/1 | 9.00 | £18.00 | £16.00 | 11.11% |
| 9/1 | 10.00 | £20.00 | £18.00 | 10.00% |
| 10/1 | 11.00 | £22.00 | £20.00 | 9.09% |
| 11/1 | 12.00 | £24.00 | £22.00 | 8.33% |
| 12/1 | 13.00 | £26.00 | £24.00 | 7.69% |
| 13/1 | 14.00 | £28.00 | £26.00 | 7.14% |
| 14/1 | 15.00 | £30.00 | £28.00 | 6.67% |
| 15/1 | 16.00 | £32.00 | £30.00 | 6.25% |
| 16/1 | 17.00 | £34.00 | £32.00 | 5.88% |
| 18/1 | 19.00 | £38.00 | £36.00 | 5.26% |
| 20/1 | 21.00 | £42.00 | £40.00 | 4.76% |
| 25/1 | 26.00 | £52.00 | £50.00 | 3.85% |
| 33/1 | 34.00 | £68.00 | £66.00 | 2.94% |
| 40/1 | 41.00 | £82.00 | £80.00 | 2.44% |
| 50/1 | 51.00 | £102.00 | £100.00 | 1.96% |
| 66/1 | 67.00 | £134.00 | £132.00 | 1.49% |
| 80/1 | 81.00 | £162.00 | £160.00 | 1.23% |
| 100/1 | 101.00 | £202.00 | £200.00 | 0.99% |
How to Convert Fractional to Decimal Odds and Vice Versa
Converting fractional to decimal odds can be completed with the following formula:
Decimal Odds = Fractional Odds + 1
Converting decimal to fractional odds can be completed with the following formula:
Fractional Odds = Decimal Odds – 1
That almost sounds too easy – so how does it work in practice?
Converting Fractional to Decimal Odds Example
Given the fractional odds of 5/2, we can use the formula to find the decimal odds conversion:
Decimal odds = 5/2 + 1 = 7/2 = 3.5
Converting Fractional to Decimal Odds Example 1
Given the fractional odds of 4.00, we can use the formula to find the decimal odds conversion:
Fractional odds = 4.00 – 1 = 3
As 3 is a whole number, it can be expressed as 3/1 in its simplest fractional form.
Converting Fractional to Decimal Odds Example 2
Given the fractional odds of 3.75, we can use the formula to find the decimal odds conversion:
Fractional odds = 3.75 – 1 = 2.75
2.75 can be expressed as 11/4 in the simplest form. This is because 2.75 must be multiplied by 4 to find the smallest whole number of 11.
((2.75/1)*4 = 11/4)
How Do +/- Odds Work?
The + and – odds in sports betting are exclusively reserved for American (Moneyline) betting and are used to inform the bettors which outcomes are favourable and which are unfavourable.
Positive Odds
Positive odds are used to indicate how much profit a bettor could earn on a $100 wager.
Example: With the Moneyline odds of +150, a $100 wager has the potential to earn a $150 profit (not including the original stake).
Negative (-) Odds
Negative odds are used to indicate the size of the wager that should be placed to earn $100.
Example: With the Moneyline odds of -200, a $200 wager must be placed to earn a $100 profit (not including the original stake).
Is it Better to Bet Plus or Minus?
Deciding on a positive or negative bet is more closely related to the value of the bet than the +/- sign.
Underdogs (positive odds) will benefit from a larger payout but are less likely to settle as a win. Favourites (negative odds) are just that – they’re the favourites. These bets are more likely to land but the payouts will be smaller.
Commonly Seen Sports Betting Odds
The below fractional odds are some of the most popular odds used by modern bookmakers. Use these as a reference or as further examples to understand the fractional patterns.
- What does 1 to 2 odds mean – Bettors must wager £2 to win £1.
- If a bettor wagers £20 at 1 to 2 odds, they will receive a profit of £10. The bet will return £30 including their original stake.
- What does 3 to 1 odds mean – Bettors must wager £1 to win £3.
- If a bettor wagers £10 at 3 to 1 odds, they will receive a profit of £30. The bet will return £40 including their original stake.
- What do 10 to 1 odds mean – Bettors must wager £1 to win £10.
- If a bettor wagers £10 at 10 to 1 odds, they will receive a profit of £100. The bet will return £110 including their original stake.
- What does 20 to 1 odds mean – Bettors must wager £1 to win £20.
- If a bettor wagers £5 at 20 to 1 odds, they will receive a profit of £100. The bet will return £105 including their original stake.
- What does 7 to 1 odds mean – Bettors must wager £1 to win £7.
- If a bettor wagers £15 at 7 to 1 odds, they will receive a profit of £105. The bet will return £120 including their original stake.
- What do 8 to 5 odds mean – Bettors must wager £5 to win £8.
- If a bettor wagers £25 at 8 to 5 odds, they will receive a profit of £40. The bet will return £65 including their original stake.
Use the top number (numerator) in the fractional display as the payout and the bottom number (denominator) as the wager needed to earn the payout.
Things You Should Know Before Making a Decision
Converting between fractional, decimal and moneyline odds is just one part of the puzzle.
It’s down to you, as a bettor, to take full responsibility for the bets that you place. Think about the following before placing any bet.
Understand the Odds
Converting the odds is one thing, but asking “how do odds work” and fully understanding what betting odds mean is another.
Try to think less about the return and more about the probabilities that the odds are trying to describe. An 80/1 return is much more likely to get bettors excited but think about it as a probability. There’s just a 1.23% chance that the bet will settle as a win.
Compare this to a bet with the odds of 2/1 or even 3/2 and the settlement of a win is much more likely.
Implement a Betting Strategy
Implementing a betting strategy is valuable to any bettor and helps sports fans capitalize on their knowledge of their favourite sport.
A passionate football fan will have more insight into the Premier League than a scratch golfer, while a scratch golfer will probably know a lot more about the PGA Tour than the average football fan/
Essentially, you should always stick to your specialist subjects. Bet on what you know and what you’re happy to research – the more data and information that you have on the players, teams, stadiums, etc. the more likely your betting strategy will pay off.
Advance to Acca Betting
Accas, or accumulators, allow bettors to combine multiple single bets into a single wager, multiplying the odds with each additional selection.
This method allows for large returns from selections with smaller odds and plays to the strategy of sports betting.
For example, in an accumulator with four selections (decimal odds 1.4, 1.5, 2.0 and 2.5), a £5 stake has the potential to earn a return of £52.50 (£5 x 1.4 x 1.5 x 2.0 x 2.5). Using the same £5, we could wager £1.25 on each of the separate selections to earn a total of £9.25 (£1.25 x 1.4) + (£1.25 x 1.5) + (£1.25 x 2.0) + (£1.25 x 2.5).
With the accumulator, the payout from these four selections using the same total wager is more than 5.6x larger. The only downside is that all selections must settle as a win. Any losing selection will forfeit the entire betslip.
Summary on How Do Odds Work
Learning how to read odds is one of the core principles of sports betting and should be fully understood before developing a betting strategy.
The ability to comprehend and convert different odds formats – fractional, decimal, and American (moneyline) – helps bettors fully grasp the probability of each betting outcome.
Modern bookmakers regularly allow users to toggle between different odds formats. However, we recommend that British and Irish bettors learn to read fractional odds, as this is the most commonly used type in the UK and Ireland.