Трудно понять, что вы имеете в виду, но вы можете попробовать это:
Sub test3()
Dim Startdate As Date, EndDate As Date, AdditionalDate As String
Dim DatesDiff As Integer
Dim i As Integer
Dim LastRowA As Long
Startdate = Format(CDate("01/01/12"), "DD/MM/YYYY")
EndDate = Format(CDate("01/04/12"), "DD/MM/YYYY")
If Sheet1.Range("A1").Value = "" Then
Sheet1.Range("A1").Value = Startdate
Else
LastRowA = Sheet1.Cells(Sheet1.Rows.Count, "A").End(xlUp).Row
Sheet1.Range("A" & LastRowA + 1).Value = Startdate
End If
DatesDiff = Month(EndDate) - Month(Startdate) - 1
For i = 1 To DatesDiff
AdditionalDate = Left(CStr(Startdate), 2) & "/" & (Month(CStr(Startdate)) + i) & "/" & Right(CStr(Startdate), 4)
LastRowA = Sheet1.Cells(Sheet1.Rows.Count, "A").End(xlUp).Row
Sheet1.Range("A" & LastRowA + 1).Value = CDate(AdditionalDate) 'Format(CDate(AdditionalDate), "DD/MM/YYYY")
Next i
LastRowA = Sheet1.Cells(Sheet1.Rows.Count, "A").End(xlUp).Row
Sheet1.Range("A" & LastRowA + 1).Value = EndDate
End Sub