Getting a Grand Average of Counts in a Pivot Table next to the default Grand Total

Dear Forum,

I need to get the Average of the Counts used in my Pivot Table, I have three Column Data
1. Col A- Branch - Name of the Branches
2. Col B- File No - Actual File Nos
3. Col C- Month- Contains Apr-19,May-19,Jun-19 and Jul-19

Now I have the Branch in my Row Section of the Pivot table, the Month in the Column Section and the File No in the Data Values where I am taking the Count.
I get the Grand Total by default, however I need to get the Average of the Counts of File Nos of the months in consideration.
I managed to do somehow using a Calculated Item however I have to manually add all the items of the months , I need a mechanism where the months get added automatically each month once the data increases every month as this is Year-To-Date Data.

In my workaround, I have created a Calculated Item to get the Grand Average of Counts and also the Grand Total , however it does not include any new months added in the data as I need to manually add it to the items, so is there a workaround without using any helper Columns in the data as i need to get this as a ready-made structure in the Pivot Table.

I can always do the Average Calculation next to my Pivot table however I need it as a part of the Pivot table.

Warm Regards
e4excel