How do betting odds work?

Welcome to this William Hill guide on betting odds. Here you will learn everything there is to know about betting odds, how to read different configurations, the best ways to utilise your preferred format, and how to convert betting odds.

It is essential to understand how betting odds work when preparing to make a bet. A lack of comprehension of the basic fractional or decimal odds could lead to losses by placing a wager you thought was something else.

Even bettors that are experienced using one format of odds, fractional, for example, can benefit from understanding the full spectrum of betting odds. They may find that utilising multiple formats aids their betting success more than relying on one kind.

What are betting odds?

Betting odds are the odds on a particular outcome and are determined by the bookmaker. For example, England to win the World Cup is 7/1 with William Hill at the time of writing this article.

Betting odds are the ratio between the amount staked by the bookies and the bettor, so 7/1 means the bookies stake seven times the amount the bettor has wagered. If the bettor wins; their predicted outcome materialises; they will take seven times their bet from the bookie (in this case).

For example, if you were to stake £1 then you would receive £8 back from the bookmaker in this case – £7 profit plus your initial stake.

How are betting odds calculated?

The odds are calculated by the bookmaker. They will estimate the probability of an event taking place and based on their prediction, will display odds.

For example, if Senegal were thought to have a low chance of winning the World Cup, the odds for it to happen would likely be a round 80/1, showing the slight chance of it occurring and the high potential payout a bettor would receive were it to happen.

William Hill offers the reader and bettor the opportunity to request their own odds. Through the popular #YourOdds on Twitter, punters can request odds on an outcome not listed by the bookie at the time and be one of the first to place a bet on a specific outcome of their choice.

The social media team will pass on the punter’s requests to the traders upstairs, and if the request is approved, the punter will be able to bet on their own fully customised odds on the day they requested them before anyone else.

How to read betting odds?

You are looking for odds on something you want to bet on? On William Hill’s website, you will find the odds you are looking for and a breakdown of what the odds are for specifically.

William Hill offers odds for many different aspects of an individual event. For example, for a football match, you could bet on goals scored, yellow cards, fouls, corners in the first half or the final score. Each outcome will have been priced up individually based on the probability of it happening.

You will likely come across fractional odds first when looking for betting odds. Fractional odds, for example, show us our potential winnings if we wager the corresponding stake. The number on the left-hand side is your winnings if you were to stake the figure on the right-hand side. For example, with odds of 10/1, £10 would be your winnings if you placed a £1 bet and won.

To read the betting odds, click on the event you are interested in and take note of the odds listed. They will be fractional, in decimal or American format, each of which will be explained below.

Fractional odds

Fractional odds use a fractional format to display possibility of an event happening. This is one of the most straightforward ways of determining how much you will win from a bet and is a quick and simple way to understand the probability of an event happening.

Here are some examples of fractional bets, how they would work and how much the bookies will pay out for a win.

• 3/1 – Bookies pay £3 for every £1 staked
• 15/2 – Bookies pay £15 for every £2 staked
• 3/5 – Bookies pay £3 for every £5 staked
• 1/1 – Bookies pay £1 for every £1 staked

The first two bets are called “odds-against” bets: a scenario where the bookie thinks the event is more likely not to happen – the bookie is betting against an event occurring and that it is unlikely.

The third one is an “odds-on” bet: a scenario where the bookie thinks the event is likely to happen.

When both numbers are the same (last example), this is an “evens” bet: a 50/50 bet. In this scenario you would double your stake if placing a winning bet.

Fractional odds to percentages

Before making a bet, a bettor may want to take into account the profit and their wager to work out the percentage return if they win.

For example, odds of 3/1 would provide a 300% profit as the payout from the bookie, as well as 100% of the money wagered. If the bettor wagered £10 and won, their profit would be £30 + the bet of £10 = a return of £40.

To convert fractional odds to percentages, use the formula (x / y) * 100 with x/y representing the fraction.

A bet of £10 with the odds 7/3.
(7 / 3) * 100 = 233.3%.

233.3% of £10 = £23.33 profit. Add the wager to the won amount = £33.33 return.

Converting fractional odds to probability

When presented with fractional odds, it can sometimes be very easy to determine the probability of an occurrence, but at other times it might not be so simple.

Knowing the probability of an outcome can be essential to bettors who are perhaps not as well informed on a certain event, so if you want to put a bet down but would like to understand how likely the outcome is with data and a fixed probability, use the formula (y / (x + y)) * 100 where odds equal x/y.

Example

Odds: 3/1
(1 / (3 + 1)) * 100
(1 / 4) * 100
0.25 * 100
25% probability of winning

Odds: 7/3
(3 / (7 + 3)) * 100
(3 / 10) * 100
0.3 * 100
30% probability of winning

Odds 1/1
(1 / (1 + 1)) * 100
(1 / 2) * 100
0.5 * 100
50% probability of winning which is why odds of 1/1 is called “evens”.

It is always worth considering that the odds displayed and offered by bookies are always probability based and can never be made as a guarantee that a certain event will happen.

Now that you have a good understanding of fractional odds and probability and are ready to start weighing up individual bets. William Hill provides unmatched betting odds across sports, television, politics and more.

Decimal odds

Another format of odds that is popular among punters is decimal odds. Decimal odds use a decimal format to display the stakes and are usually utilised for a quick view of the probability of an event.

Decimal odds also make it easier for punters to compare odds without complicated mathematical formulas and allow for a quick view of potential winnings. The higher the number, the higher the potential winnings.

The William Hill website allows bettors to choose between their preferred odds format, be that decimal or fractional.

To work out winnings, you need to multiply the stakes by the odds:

• 5.00: Bet £1, win £5
• 5.00: Bet £5, win £25
• 2.00: Bet £3, win £6 (equivalent to 1/1 evens)

Decimal odds to percentages

To calculate the winning percentage when betting with decimal odds, multiply the decimal by 100 to get the percentage. E.g. 1.20 = 120%.

This percentage is not the profit but the amount wagered.

For example, a bettor wages £10 with the odds at 1.20.
1.20 * 100 = 120%
£10 * 120% = £12
The bettor wins 120% of their original wager back with a successful bet.

Convert decimal odds to probability

To convert decimal odds to a probability you need to take into account the value of the decimal. Odds of 2.00 is the same as a 50% chance of winning. Odds above 2.00 has a lower than 50% chance of winning and vice versa.

To turn decimal odds into probability, use the formula 100/odds.

For example, if the team’s odds of winning is 6.00, the probability of them winning is 100/6, which equals 16.7%.

Always remember that the odds displayed and offered by bookies are always probability based and should never be interpreted as a guarantee that a certain event will happen.

Use what you have learnt and Check out William Hill’s latest sports betting odds.

American money line odds

American odds are also called money line or US odds. These are the odds format primarily used in the US and will rarely get adopted by bookmakers from the United Kingdom.

They can be confusing compared to fractional or decimal odds until you have got the hang of them.

They are displayed with either a positive or minus number:

Underdog

A positive number indicates how much profit you will get if you bet £100.

Favourites

Indicates what you must bet to make £100 profit.

Here are some examples of US bets, how they would work and how much the bookies will pay out for a win.

• +250: Bet £100, win £250, profit £350
• +250: Bet £10, win £25, profit £35
• -125: Bet £125, win £25, profit -£100
• -125: Bet £10, win £2, profit -£8

American odds to percentages

To convert US odds to percentages, use these rules:

Underdogs
The odds themselves are the profit therefore the percentage of return is the odds + 100% of the wager. You can use this to work out how much money will be returned if you win.

With odds of +250 this equals 250%. If you wager £100, with a successful bet you would profit £250 including the betted £100 equaling 350%.
100 * (250 + 100)
100 * 350 = £350

Favourites

To convert favourites odds to a percentage, use the formula 100 – (10000 / +odds)

For example. the bettor bets £100 with -125 odds.

100 – (10,000 / +125) = 20

This equals 20% of what you wagered. Therefore £100 * 20% equals a £20 return or an £80 loss.

Converting American odds to probability

Underdogs
To calculate the probability from an underdog American odds, use the same method as fractional odds. Using the example +250 odds with a £100 bet. Divide the odds by 100 and use the formula (y / (x + y)) * 100 where odds are x/y.

(1 / (2.5 + 1)) * 100
(1 / 3.5) * 100
0.2857 * 100
28.57% win probability

Favourites
To calculate the probability from a favourites American odds, use the same formula as above but subtract the final number from 100.

100 – ((1 / (2.5 + 1)) * 100)
100 – ((1 / 3.5) * 100)
100 – (0.2857 * 100)
100 – 28.57
71.43% win probability.

Use what you have learnt and Check out William Hill’s latest sports betting odds.

Converting betting odds

The William Hill website automatically does this for you. On desktop you can see the option to change the odds format in the top right. On mobile, this is located at the bottom of the menu.

How to convert decimal odds to fractional odds?

To convert decimal odds to fractional odds use the formula (x – 1.00) and place over 1.

For example:
6.00 odds
6.00 – 1.00 = 5.00 = 5/1

You may need to simplify the fraction like this more complicated example.
5.50 odds
5.50 – 1.00 = 5.5/1 = 11/2

How to convert decimal odds to American odds?

To convert decimal odds to American odds, you will need to determine which formula you use based on the decimal value.

For decimal odds 2.00 or greater use the formula (decimal odds – 1) * 100.

Example:
(3.56 – 1) * 100
2.56*100 = +256

For decimal odds lower than 2.00 use the formula -100 / (decimal odds – 1).

Example:
-100 / (1.20 – 1)
-100 / 0.20 = -500

How to convert fractional odds to decimal odds?

To convert fractional odds to decimal odds use the formula:

If the fraction is x/y then (x / y) + 1.00

Example:
(5 / 1) + 1.00
5 + 1.00 = 6.00

Or a more complicated example:
(7 / 3) + 1.00
2.33 + 1.00 = 3.33

How to convert fractional odds to American odds?

To convert fractional odds to American odds you need to determine what formula to use based on the fraction value if the fraction is equal to x/y.

For fractions greater 1, use the formula (x / y) * 100.

Example:
5/1 Fractional odds
(5 / 1)*  100
5 * 100 = +500

For fractions lower than  1 use the formula -100 / (x / y)

Example:
3/7 Fractional odds
-100 / (3 / 7)
-100 / 0.4286 = -233

How to convert American odds to decimal odds?

To convert American odds to decimal odds, you need to choose the formula based on whether the American odd is an underdog (positive number) or a favourite (negative number).

Underdogs

To convert underdog odds to decimal odds use the formula (+x /100) + 1

+400 American odds
(400/100) + 1
4+1 = 5.00

Favourites

To convert favourite odds to decimal odds 100 divided by the positive moneyline amount and add 1.
(100 / +x) + 1

-400 American Odds
(100 /400) + 1
0.25 + 1 = 1.25

How to convert American odds to Fractional odds?

To convert American odds to decimal odds, you need to choose the formula based on whether the American odd is an underdog (positive number) or a favourite (negative number).

Underdogs

To convert underdog odds to fractional odds, use the formula x / 100 then simplify the fraction if possible.

Example:
+400 American odds

400 / 100 = 4/1

A more complicated example
+350 American odds
350 / 100
3.5 = 7 / 2

Favourites

To convert favourites odds to fractional odds, use the formula -100 / x

Example:
-400 American odds

-100 / -400
0.25/1 * 1000/1000 = 250/1000
The greatest common denominator is 250.
(250/250)/(1000/250)
1/4

A more complicated example:
-650 American odds
-100 / -650
0.15/1 * 1000/1000 = 150/1000
The greatest common denominator is 50
(150/50)/(1000/50)
3/20

Ready to put your new knowledge into practice? Check out William Hill’s latest sports betting odds.