Help with calculating average of previous 12 months

[Anonymous]

Hello,
Please, as it is indicated in this two attached files below, I would like to display the sum of the last 12 months, ie when I tick in my report the month of May and I check the year 2018 , I would like to calculate the average of last 12 months by counting of May (ie of me from June 2017 -> May 2018).
PS: When I select the year, the result becomes wrong

But as you look in the attached files below, for the normal sum formula and the sum of last 12 months always I had the same result when I select the year !!!!! which is too weird.
Look at these two attached files below.

Thank you a lot.
Cordially.

[TomMartens]

Hey,

please allow to me to direct your attention to this article: https://www.daxpatterns.com/time-patterns/

This article provides examples for almost every date related calculations.

It's a common best practice to create a dedicated calendar table, sometimes it's not just recommended but it becomes necessary.

Regards,

Tom