Which Filter Functions should I use with my Upper Control Limit?

[nicoportishead]

Hi everyone,

I am relatively new with DAX / Power BI and I am currently facing a problem with Filters (I think!) for creating an Upper Control Limit (UCL).

Here is the "draft" formula:

UCL = SUM(CANCELLED[cancelled])/(SUM(CANCELLED[cancelled])+SUM(CANCELLED[resulted]))+(3*SQRT(SUM(CANCELLED[cancelled])+SUM(CANCELLED[resulted])/CALCULATE(SUM(CANCELLED[cancelled]),'calendar'[calendar_date])))

And here is the kind of result I should get:

 

Now for working properly I need to apply some Filter Functions into the Formula without withdraw filters (Site and Department) already applied at the page level from Power BI desktop. 

Into the formula, I have to make sure that for each "Sum" the system sums all the previous months except for the last one.The last "Sum" must have only the Sum for the month.

Should I use "ALLSELECTED" function in my formula? Or "ALLEXCEPT"?

Or I am not in the right direction and I have to create intermediate measures?

Thank you in advance for your help.

Nico