Dynamic 2 Date Columns Difference

Hi sammy339,

Thank you for reaching out to the Microsoft Fabric Community forum.

create a mapping table first like below

DateSelector = DATATABLE("DateName", STRING, "ColumnIndex", INTEGER,{{"Column1", 1},{"Column2", 2},{"Column3", 3}})

DAX Measure:

Date Difference = 
VAR SelectedCol1 = SELECTEDVALUE(DateSelector[DateName])
VAR SelectedCol2 = SELECTEDVALUE(DateSelector2[DateName])

VAR Date1 = SWITCH(TRUE(),SelectedCol1 = "Column1", 'Projects'[Column1],
        SelectedCol1 = "Column2", 'Projects'[Column2],
        SelectedCol1 = "Column3", 'Projects'[Column3])

VAR Date2 = SWITCH(TRUE(),SelectedCol2 = "Column1", 'Projects'[Column1],
        SelectedCol2 = "Column2", 'Projects'[Column2],
        SelectedCol2 = "Column3", 'Projects'[Column3])

RETURN
IF(ISBLANK(Date1) || ISBLANK(Date2),BLANK(),DATEDIFF(Date1, Date2, DAY))

I have included the PBIX file that I created using the provided sample data. Kindly review it and confirm whether it aligns with your expectations.

If this post clears your doubt, please give us Kudos and consider marking Accepting it as a solution to guide other members in finding it more easily.

Best Regards,
Sahasra.