Need help with DAX formula for average of past transaction totals by day of month

[jbyroade]

My date table includes a column for [Previous 15 Days].  I'm filtering it for TRUE, giving me the last 15 days of data.  I have measures that show me my transaction totals for each of those 15 days as well as a cumulative total.

I want to create a new measure that will show the 12-month average for that day of the month.  I'm not sure how to write it.  If it helps, I do have a [Day Number] field on my date table.

[Anonymous]

https://www.sqlbi.com/articles/rolling-12-months-average-in-dax/

[jbyroade]

This isn't exactly what I'm looking for.  I'd like to average out the specific days of the month.  For example, the last twelve 20th day of the month.  (1/20, 2/20, 3/20....)

[Anonymous]

https://community.powerbi.com/t5/Community-Blog/How-to-Get-Your-Question-Answered-Quickly/ba-p/38490