How to calculate probabilities for football match? 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) = 0,5; 
P(Chelsea draw at home)=0,3; 
P(Chelsea lose at home) = 0,2;

P(Liverpool win away) = 0,2; 
P(Liverpool draw away)=0,6; 
P(Liverpool lose away) = 0,2;


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!
Probability of Chelsea winning would still be 0.55. It is not dependent on any other variable.  it means that,


  For any match, Chelsea probability to win is 0.55. Because in a season they win 55% of their matches.
What you have to do is to normalize the data. A simple way for it:


Add the probabilities which show the same result, to each other. In you example, you have to add Chelsea wins to Liverpool losses, Chelsea draws to Liverpool draws and Chelsea losses to Liverpool wins.


What you'll have is:

Chelsea Win: $0.55+0.25=0.80$

Draw: $0.35+0.55=0.90$

Liverpool Win: $0.10+0.20=0.30$


Then, divide those possibilities to two, to normalize the probabilities. Why two? Because you have two teams.


Chelsea Win: $0.40$
Draw: $0.45$
Liverpool Win: $0.15$

Of course, in real world it's not that simple as you have to calculate last 5 games form, injured and banned players and the statistics when they're not playing, last game score and date, games between those two teams in last 10 years etc. 

For instance, in Turkey, Galatasaray hasn't won against Fenerbahçe away in last 15 years. Even Galatasaray was way ahead champion, they just couldn't win against Fenerbahçe. So, when calculating the probable result of Fenerbahçe - Galatasaray game, you have to consider that curse. So, in any game, you can't only look at their whole season form, or only last 5 games, or only "something". You have to consider each effect, and this is what makes the calculation complex.