Calculating Difference From Previous Months

Hi All,

I have a question regarding calculating the Previous Months Increase from the Current Months , I am calculating two Measures (Calculated by Running totals) On basis of Months( Right Now they are in Day Month and Year Format which I converted into Month and Year format at Group Level) . But I want to calculate each measure increase from their Previous Month , I am providing an example how my data should look , Can you please help me out with some thoughts into it.

Date    X Customers   Y Customers  Increase in X Customer From Previous Month  Increase in Y Customer From Previous Months

02/2015   50                    70                              10                                                                      15

03/2015    80                    90                              30                                                                      20

04/2015     75                    100                            -15                                                                     10

Thanks,

Naveen