calculation on data from pivot table

Hello there,
I have a range of data that i entered in a pivot table.
the data structure is : VariableA and a date field, for instance :
VA date1
VA date2
VB date3
VC date4
VC date5...

In the pivot table i have :
VariableA in row labels.
and twice the date in Sum Values.

This format output data like this format :

VariableA MinDate MaxDate
VA date1 date2
VB date3 date3
VC date4 date5

Now, i want to insert a field in the pivot table that calculate the difference in days between a fixed date and MinDate for each row.

How i can achieve this?
what is the best way, please?

Why the 2 new fields MinDate and MaxDate doesn't appear in the field list in the "Insert calculated field" dialog box??

thanks a lot

The best way, in my opinion, is to create the formulae outside the pivot table. If the fixed date isn't in your source data it would be destructively difficult to hard-code the date into a calculated field or item, but a formula like =$A$1-G3 where A1 is your fixed date and G3 is within your pivot would just 'work'.

Sorry I didn't quite understand the feedback:

It worked... the formula you gave me don't work on pasting it

Perhaps you could upload an example showing what you're hoping to see - I can't really add any more if you don't.

you don't want getpivotdata, you just want a cell ref

As I said - example is needed, otherwise my help is a total waste of time