I have a CSV File and i want to edit it and make a new column in it

my current text in CSV file (Some)
Username,Your referral since,Last click,Clicks
R1181312,2008-06-13 16:49:00,2008-07-18 09:27:00,40
R1477140,2008-06-13 16:49:00,2008-07-17 10:18:00,73
R30994,2008-06-13 16:49:00,2008-07-18 09:47:00,87
R1310392,2008-06-13 16:49:00,2008-07-18 11:13:00,33
R290032,2008-06-13 16:49:00,2008-07-17 14:17:00,80
R328542,2008-06-13 16:49:00,2008-07-18 12:57:00,84

Now i want to do is add another column named "Average Clicks"
It should do is calculate the days from Your referral since till taday and then divide clicks by days

Is it possible?