Réponse acceptée !
cette fonction je l'utilise dans mes projets. bn chance
apel: text1.text=fundate(25/06/08)

Function Findate(X As String) As Date
Dim m, a, fj As Integer
On Error GoTo r
m = Month(X)
a = Year(X)
If m <= 7 Then
    If m = 2 Then
            If a Mod 4 = 0 Then
                    fj = 29
            Else
                    fj = 28
            End If
    ElseIf m Mod 2 = 0 Then
            fj = 30
    Else
        fj = 31
    End If
Else
    If m Mod 2 = 0 Then
        fj = 31
    Else
        fj = 30
    End If
End If
Findate = Format(fj & "/" & m & "/" & a, "dd/mm/yy")
Exit Function
r:
        MsgBox Err.Description
End Function