Dim i as Integer
Sub test()
i = 1
For i = 1 To 10 'Rows 1 to 10
    Range("B" & i).Select    'A column with old date, B column with new date
    dateStr = "=date(year(A" & i & "),month(A" & i & ")+6,day(A" & i & "))"
    ActiveCell.Value = dateStr
Next
End Sub

Sub Dateaddition()
    Dim LastCell    As Range
    Dim rngUse      As Range
    Dim cl          As Range
    
    'replacing the current cells value with an additional 6 months
    Set LastCell = Cells.Find("*", , , , , xlPrevious)
    If Not LastCell Is Nothing Then
        Set rngUse = Range(Cells(1, 1), Cells(LastCell.Row, 1))
            For Each cl In rngUse
                'remove the offset to overwrite the values
                If IsDate(cl.Value) Then _
                    cl.Offset(0, 1).Formula = DateAdd("m", 6, cl.Value)
            Next cl
    End If
    
    'get rid of object variables
    Set cl = Nothing
    Set rngUse = Nothing
    Set LastCell = Nothing
End Sub