Sub test()
Dim i As Byte
For i = 1 To 12
Worksheets.Add(after:=Sheets(Sheets.Count)).Name = MonthName(i)
Next i
End Sub
Sheets("janvier").Cells.Copy Sheets("février").Cells
Worksheets("janvier").Copy after:=Sheets(Sheets.Count)
ActiveSheet.Name = MonthName(i + 1)