Sorry. Use this one. I just removed the msgbox I was using to help me
while writing the code
Sub filldown()
Dim Lrow As Long
Dim Col As Variant
Dim i As Variant
Dim lCol As Variant
With ActiveCell
i = .Address
End With
lCol = Mid(ActiveCell.Offset(0, -1).Columns.Address, 2,
WorksheetFunction.Find("$", _
ActiveCell.Offset(0, -1).Columns.Address, 2) - 2)
Col = Mid(ActiveCell.Columns.Address, 2,
WorksheetFunction.Find("$", _
ActiveCell.Columns.Address, 2) - 2)
Lrow = Range(lCol & Rows.Count).End(xlUp).Row
ActiveCell.FormulaR1C1 = "Your Formula"
ActiveCell.Select
Selection.AutoFill Destination:=Range(i & ":" & Col & Lrow),
Type:=xlFillDefault
End Sub