Hi Compariniaa,
What about Decmber?

For a VBA solution, based on your idea
[VBA]Sub UpDate()
Dim Dy As Long, Mh As Long, Yr As Long
For Each cel In Selection
Dy = Day(cel)
Mh = (Month(cel) Mod 12) + 1
If (Month(cel) Mod 12) = 0 Then
Yr = Year(cel) + 1
Else
Yr = Year(cel)
End If
cel.Value = DateValue(Dy & "/" & Mh & "/" & Yr)
Next
End Sub[/VBA]