Option Explicit
Sub test()
Dim t As Byte, madate As Date, madate1 As Date, madate2 As Date
madate = Range("C1").Value
t = DatePart("q", madate, 2, 2)
Range("C2").Value = t & "T" & Year(madate)
Select Case t
Case 1
madate1 = DateSerial(Year(madate), 1, 1)
madate2 = DateSerial(Year(madate), 3, 31)
Case 2
madate1 = DateSerial(Year(madate), 4, 1)
madate2 = DateSerial(Year(madate), 6, 30)
Case 3
madate1 = DateSerial(Year(madate), 7, 1)
madate2 = DateSerial(Year(madate), 9, 30)
Case 4
madate1 = DateSerial(Year(madate), 10, 1)
madate2 = DateSerial(Year(madate), 12, 31)
End Select
Range("C3").Value = madate1
Range("C4").Value = madate2
Range("C5").Value = DateSerial(Year(madate2), Month(madate2) + 2, 0)
Range("C6").Value = DatePart("q", DateAdd("yyyy", -3, DateAdd("m", -1, madate)), 2, 2) _
& "T" & Year(DateAdd("yyyy", -3, DateAdd("m", -2, madate)))
Range("C7").Value = DatePart("q", DateAdd("q", 11, DateAdd("yyyy", -3, DateAdd("m", -1, madate))), 2, 2) _
& "T" & Year(DateAdd("q", 11, DateAdd("yyyy", -3, DateAdd("m", -1, madate))))
End Sub