SSRS how to get for number of months

Hi All;

below is my SSRS expression 

=Cdate(Format(Cdate(Mid(Fields!createdon.Value,4,2) & "/" & Mid(Fields!createdon.Value,1,2) & "/" & Mid(Fields!createdon.Value,7,4)),"MMMM yyyy"))

which gives me the month in MMMM yyyy format in Jan 2014, Feb 2014, Mar 2014... so on

i need to remove a average of a month 

i.e Months value/No of months

I do i get number of months dynamically in SSRS

Any help much appreciated

Thanks

Pradnya07