Sum of Invoices of a month where first date is in between that month and the two previous

[Anonymous]

Hi everyone, hope someone can help me cause I've been trying to achieve this for days and I couldn't get it.

What I'm trying to get is a pivot table with two dimensions; Year and Month. The expression I need is the sum of the invoices amount of all the customers which first date of invoice is between the last day of the month of the dimension and the first day of the two previous months of that value of the dimension. So for the Nov-2016 I need all the invoices in November which first Invoice Date is between 01/09/2016-30/11/2016.

For example if I have the following values

the pivot table I need is this one:

Thanks in advance for your time.

[Anonymous]

Yeah It works. Thank you very much.