' I almost never work with drop-down lists in Excel, and have never tried to make them work with VBA. So I'm
' going to pretend that once a user has selected the value in the list, it's available as that cell's Value property.
Set owb = ThisWorkbook
Set ows1 = owb.Worksheets("Sheet1")
DropDate = ows1.Cells(3, 11).Value 'row 3, column 11
' Now look for DropDate in Average Balance sheet. You can use the Excel Find method, but here I'll show you how to do it manually:
Set owsA = owb.Worksheets("Average Balance sheet")
For jc = 1 to 26 'arbitrarily saying we won't look further than column Z
' Look in row 2, columns A through Z:
If owsA.Cells(2, jc).Value = DropDate Then Exit For
Next jc
If jc > 26 Then 'it went all the way from A to Z without finding that date
MgsBox "Target date " & DropDate & " not found in " & owsA.Name & "."
Exit Sub
End If
' Now jc is the column where we found DropDate. Do the Insert.
owsA.Columns(jc + 1).Insert
' Next we have to calculate a date that's one month later than DropDate. But let's pause here to breathe.