It is important to know that when using Table Calculations, they are calculated based on whatever is in the view. If certain months are filtered out then the calculation will only be on those values available. To get around this, you can hide the unwanted values. Create a parameter that allows the user to select the month. Then, create a calculated field that is similar to the following
if [date]=[date parameter] then 'show' else 'hide' end
Place this calculation on the rows or columns shelf, right click on the 'hide' header and select Hide.
Hope this helps!
Can you please provide a sample packaged workbook with data that represents your situation, and detail what you expect for results and interaction? Thank you.
I actually ended up just doing the calculation outside of Tableau and importing the fields I wanted. I think that was the easiest solution.