DAX Looping Variable - powerbi

Question

I'm building a Power BI dashboard that includes actual cost vs budget. Summarizing the cost is not a problem. The budget amount is entered in a table as a weekly amount, for example $1,000. We use a custom accounting calendar that dictates the number of weeks per month. The second month of each quarter is 5 weeks while all other months are 4 weeks. Here's what it looks like:
January is 4 weeks
February is 5 weeks
March is 4 weeks
April is 4 weeks
May is 5 weeks
June is 4 weeks
July is 4 weeks
August is 5 weeks
September is 4 weeks
October is 4 weeks
November is 5 weeks
December is 4 weeks
I need a looping variable in DAX that will simply count the number of weeks based on the months chosen with the month slicer. Then I can multiply the number of weeks by the weekly budget amount.
Here's a practical example:
If I choose Jan, Feb, Mar, Apr then the number of weeks should be 17 weeks. And the budget amount should be $17,000.
I figured this out in Crystal Reports. Here's the formula I wrote:
local datetimevar startdate:= {?BegMonth};
local numbervar numofWeeks;
While startdate <= {?EndMonth}
Do(
if month(startdate) in [2,5,8,11] then
numofWeeks := numofWeeks + 5
else
numofWeeks := numofWeeks + 4;
startdate := DATEADD("m",1,startdate);
);
numofWeeks
I've tried several approaches with DAX but I got nothing to work.

Answer 1

DAX doesn't exactly do looping. It does aggregations on filtered columns.
If you don't have a Month column, then create a calculated column.
TableName[Month] = MONTH ( TableName[Date] )
Once you have that, adding up weeks can be done with an iterator function.
Weeks =
SUMX (
VALUES ( TableName[Month] ),
IF ( TableName[Month] IN { 2, 5, 8, 11 }, 5, 4 )
)
The VALUES function is a list of unique values in the filter context, so if you selected Jan - Apr, then it would be {1,2,3,4}. Then SUMX iterates ("loops") over those four values and add 5 or 4 depending on the condition specified in the IF function.