LastRow

Sub DateValueConvert()
'
' DateValueConvert Macro
'
    Application.ScreenUpdating = False
    
    Dim lastrow As Long
    lastrow = ActiveSheet.Cells(Rows.Count, "B").End(xlUp).Row
         
    Selection.EntireColumn.Insert , CopyOrigin:=xlFormatFromLeftOrAbove
    Range("A2:A" & lastrow).Formula = "=DATEVALUE(RC[1])"
    'ActiveCell.FormulaR1C1 = "=DATEVALUE(RC[1])"
    'ActiveCell.Select
    'Good Below - fix range? - fills the column w/ formula
    'Selection.AutoFill Destination:=ActiveCell.Range("A1:A3595")
    'Stackoverflow copy - works
    'Range(Selection, Selection.End(xlDown)).Select
    'Selection.FillDown
    'selects and copys columns for da paste
    ActiveCell.Range("A1:A" & lastrow).Select
    Selection.Copy
    ActiveCell.Offset(0, 1).Range("A1").Select
    Selection.PasteSpecial Paste:=xlPasteValues
    ActiveCell.Offset(0, -1).Columns("A:A").EntireColumn.Select
    Selection.Delete Shift:=xlToLeft
   
   
End Sub