vba - autofill down according to adjacent column

Question

I'm looking for VBA code that will autofill data down according to the length of an adjacent column. I know there are a few ways to go about this, but which is best?:

If LastRow > Selection.Row Then
   Range("D2").AutoFill Destination:=Range("D2:D" & LastRow)

or something like:

If Not IsEmpty(ActiveCell.Offset(0,1)) Then
   Range("D2").AutoFill Destination:=Range("D2:D" & LastRow)

I'm pretty sure neither of these work exactly how I want it so what am I missing?

Answer 1

There is no need for any if condition. We can get the last used row of column C and fill the data in column D accordingly.

Sub test()

    Dim lastRow As Long
    lastRow = Range("C" & Rows.Count).End(xlUp).Row
    Range("D2").AutoFill Destination:=Range("D2:D" & lastRow)

End Sub