# Calculation of Odds: Probability and Deviation

Calculating odds is a science, and statisticians/analysts, who can do the job competently, receive good annual salaries (GBP 50k-80k; €60k-95k: Quantitative Analyst).

These jobs are paid so well because the results form the backbone of each bookmaker’s business. The better an analyst understands his job, the bigger the potential profit margins for the bookmaker. In order to make long-term profits, a good understanding of odds calculation is therefore also essential for any bettor.

Image: alphaspirit (Shutterstock)

### Probability of Football Match Results

Odds are based on the probability that a certain event occurs: for example a home win, a draw, or an away win in football games based on historical data. But what is the current probability of each of these outcomes and how are percentages computed? Also, from where does one get the data from?

The following diagram shows the distribution of results for the English Premier League for home win, draw, and away win during the last five complete seasons:

Results: English Premier League - 2005 to 2010 – Diagram

Looking at the graph, one can see that the distribution of results is rather similar for each year.

Without considering factors such as matches between strong or weak teams, teams under new management, rain affected games or anything else one can think of, fixtures in the English Premier League, according to the statistics, show on average 24.46% of all games were drawn, 27.35% ended in an away win and 48.16% were won by the home team:

Results: English Premier League - 2005 bis 2010 – Data from: www.sportpress.com

Only twice (of 15) did results fall outside of ± 2% residual from the average figures, being drawn games in 2005/2006 (-4.2%) and away wins in 2009/2010 (-3.4%):

Absolute deviation: English Premier League 2005 to 2010

Last Update: 11 March 2011

### 16 Responses to “Calculation of Odds: Probability and Deviation”

1. bester
11 March 2012 at 6:11 pm #

the stuff you publish kicks ass. thanks!

2. Ian538rygby
22 March 2012 at 9:10 am #

just found your blog……I am not usually prone to participating on forums or blogs, but I have been fascinated, reading your articles, and thought your efforts deserve to be acknowleged.

3. Ian538rugby
22 March 2012 at 9:13 am #

4. Soccerwidow
22 March 2012 at 9:16 am #

Ian, thank you for your very kind words

5. 22 March 2012 at 12:08 pm #

Thanks for a well written an easy to follow article – something thats pretty rare on the subject of calculating football odds.

6. Soccerwidow
23 March 2012 at 11:58 pm #

Thank you, Rick. We try our best!

7. Helder
13 July 2012 at 2:51 pm #

Hi Soccerwidow,

Glad to see the website is up and running again. I would like to ask you a question regarding the non arithmetical calculation of odds in the “Calculation of Odds” section.

In your example you, the calculated odds are found by using the 5-year mean of 48,16% (home wins). You therefore assume that for every game the odds to back the home team are of 2,08. You then use the found relative deviation the calculate the minimum and maximum odds.

If we were to calculate the odds based on reality, we would have to find the probability of the home team winnning, instead of using the 5-year average mean of 48,16%. Once we find the real odds we could then calculate the maximum and minimum odds (using the 5-year relative deviation), to which we would compare the market odds given to us.

Is this train of thought correct?

8. Helder
15 July 2012 at 8:55 pm #

Thank you for your help, those articles are very good and they have helped me clarify certain aspects. But with everything, the more you more learn the more questions you have If you don’t mind could you give me your opinion on the following question?

Let’s say that I like to bet on certain events that have a high probability of happening (low odds), then I would have to:

– Find something to bet on that is statistically a sure thing. In other words a high probability and a small relative deviation over time (for instance backing Team A at home).
– Find an edge and only bet on over value home games by checking head-2-head statistics.
– Create a staking plan.

If we were to compare this strategy to one where we bet sistematicaly on every Team A home game, could we say that one is more reliable than the other, or more profitable in the long run, or is it just a personal preference?

• Soccerwidow
15 July 2012 at 9:20 pm #

Without having calculations and numbers in front of me I cannot say which strategy is more reliable. Each strategy needs to be individually evaluated in detail before a statement can be made.

However, what I can say is that in the end it really doesn’t matter. You pick any strategy according to your personal preferences, and get your teeth into it. I promise that you will be able to make it a successful strategy if you don’t give up too early, and calculate and think everything through. Though it may take a long while.

One of the main mistakes unsuccessful bettors do is that they keep “shopping round”, trying one strategy for some time, then the next, and then again another. Your own time resources are one of the largest issues. Therefore it’s crucial to spezialise in order to succeed.

9. A. smith
8 April 2013 at 6:45 pm #

How come you don’t include missing/injured players in the calculations?

• Soccerwidow
9 April 2013 at 6:09 am #

Missing/insured player have a far less effect (if at all) on the final distribution of results than commonly believed. Football is a team sport. In professional football there are lots of players employed. All of them professionals. Bookmakers set their odds weeks, sometimes months, in advance. This should tell you something about the importance of injuries/ missing players for odds calculation.

In the “normal world” it’s only very tiny and poor companies with very few employees which suffer if a major employee is missing. In larger companies a sick note from an individual will hardly affect the overall performance of a company’s results.

10. Autumn
20 April 2013 at 2:13 pm #

Hello, just to ask, how do you think chaos theory would affect the results of a soccer match? Like for example, in terms of 1) movements of the ball and 2) behavioural aspects. Thank you!

• Soccerwidow
24 April 2013 at 6:14 am #

Chaos theory is very, very advanced maths, and goes far beyond the simplified explanations in this blog which are aimed at readers with more basic maths skills.

However, to answer your question: Yes, of course. If you are familiar with chaos theory and advanced statistics, then apply them to your calculations and predictions of match results! This will certainly lead to quite accurate results.

Try also search engines for the keywords chaos theory football. This will bring up a good number of academic articles on this subject.

11. Ineedscore
22 November 2013 at 10:24 am #

Hello guys! I am looking for the acceptible methods to calculate probability chances “1 x 2″ on football matches. I read a lot of articles, but there are no useful information that can help me. I started to investigate probability theory myself and I freezed after some calculations.
Let imagine we have match between Chelsea and Liverpool. I understand how calculate probabilitly for each team. I took last ten Chelsea’s home matches and last ten Liverpool’s away matches. After simple calculations(win/10; draw/10; lose/10) I received:
P(Chelsea win at home) = 0,55;
P(Chelsea draw at home)=0,35;
P(Chelsea lose at home) = 0,10;

P(Liverpool win away) = 0,20;
P(Liverpool draw away)=0,55;
P(Liverpool lose away) = 0,25;

But I could now understand how to use this calculated data to predict match Chelsea – Liverpool. I tries to apply sum and multiplication theorems, but there could be incredible result, for exmaple over 1. I definetly understand that this calculation would be very approximatly and that there are a lot of parameters that affect on football result, but I think that it could be useful to predict match. Thank you for any help!

• Soccerwidow
22 November 2013 at 10:51 am #

Hi Ineedscore, have a look at our Value Calculator: True Odds & Value Detector: League Games with H2H History as it may help you to answer your question.

There is no need to apply any sum or multiplication theorems. It’s far less difficult that this.