Need a variable

[#1]

Hi i have a requirement which needs the exact formula. I have attached the table chart, which exactly shows the formula. I need the formula for Average visits per user per month  =

  (# of visits / Unique Users actually accessing QV) / (# of months) which is

=((Count(Distinct(if(Year([MONTH_END_DT])=Year([MinDateVar]),[Timestamp],0))))/(Count(distinct(if(Year([MONTH_END_DT])=Year([MinDateVar]),[User_Pin_Key],0)))))/???????

I want the formula for (# of months) which is the number of document accessed by a user in a month. It should be a variable. Since it may vary for different user accessing a document for different month.