Sub f()
Dim nn As String 'nn: new number
Dim dern As String
'Find the last used cell, before a blank in a Column:
dern = Range("A1").End(xlDown).Value
'année
If Left(dern, 2) = Mid(Year(Date), 3) Then
nn = Mid(dern, 1, 2)
Else
nn = Mid(Year(Date), 3)
End If
'mois
If Mid(dern, 3, 2) = Format(Month(Date), "00") Then
nn = nn & Mid(dern, 3, 2)
Else
nn = nn & Format(Month(Date), "00")
End If
'incrément
If Left(dern, 2) = Mid(Year(Date), 3) And Mid(dern, 3, 2) = Format(Month(Date), "00") Then
nn = nn & Format(Mid(dern, 5, 2) + 1, "00") & "A"
Else
nn = nn & "01A"
End If
'Range("A1").End(xlDown).Offset(1, 0).Value = nn
End Sub