datedif Function, only for working days (mon-Fri)

Hi BachFel,

I would follow the following approach. 

First, I would create a disconnected calendar table ( a table that has no relationship with your Fact table) either in DAX or in M which contains all the dates that my fact table has. The calendar table would indicate 1 if a day is a weekday and 0 if otherwise. Here's my DAX formula:

Calendar (Disconnected) =
VAR START_DATE_ =
    DATE ( 2018, 3, 1 )
VAR END_DATE_ =
    DATE ( 2018, 4, 20 )
VAR DATES_ =
    CALENDAR ( START_DATE_, END_DATE_ )
RETURN
    ADDCOLUMNS (
        DATES_,
        "Name of Day", FORMAT ( [Date], "ddd" ),
        "Is Weekday?", IF (
            FORMAT ( [Date], "ddd" ) = "Sat"
                || FORMAT ( [Date], "ddd" ) = "Sun",
            0,
            1
        )
    )

You may edit the START_DATE_ and END_DATE_ variables above as desired.

In my fact table, I would create a calculated column that sums the value in Is Weekday? column fromt the disconnected calendar table filtered by a specific date till today. Here's my DAX formula: 

Workday Difference =
    CALCULATE (
        SUM ( 'Calendar (Disconnected)'[Is Weekday?] ),
        DATESBETWEEN ( 'Calendar (Disconnected)'[Date], 'Fact'[Date], TODAY () )
    )
        - 1

Notice that added -1 after the latest parenthesis. This is  because the sum that is being returned is the sum from start to end dates and not the difference between the two.