Sub Date_de_bas()
With Sheets("1 - Feuille").[F5]
If Not IsDate(CStr(.Value)) Then mois = "" Else mois = Month(.Value)
End With
Select Case mois
Case 1, 2, 3: [F9].Value = DateSerial(Year:=Year([F5]), Month:=7, Day:=1)
Case 4, 5, 6: [F9].Value = DateSerial(Year:=Year([F5]), Month:=10, Day:=1)
Case 7, 8, 9: [F9].Value = DateSerial(Year:=Year([F5] + 1), Month:=1, Day:=1)
Case 10, 11, 12: [F9].Value = DateSerial(Year:=Year([F5] + 1), Month:=4, Day:=1)
Case Else: [F9].Value = ""
End Select
End Sub