WD97: Macro to Determine the Number of Days in a Specified Month

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   Sub Date_NumDaysInMonth()
      Dim iMon As Integer
      Dim sDate As String
   PromptForDate:
      sDate = InputBox("Enter a date in the mm/dd/yyyy format")
      ' If Cancel was pressed, end macro.
      If sDate = "" Then Exit Sub
      ' If Date entered is not a valid date, display message.
      If Not IsDate(sDate) Then
         MsgBox "Please enter a valid date."
         GoTo PromptForDate
      End If
      ' The Month function returns the month number (1-12) of the date.
      Select Case Month(sDate)
         Case 4, 6, 9, 11
            sNumDays = "30"
         Case 2
            If Year(sDate) Mod 4 = 0 Then
               sNumDays = "29"
            Else
               sNumDays = "28"
            End If
         Case Else
            sNumDays = "31"
      End Select
      MsgBox Format$(sDate, "mmmm") & " of " & Format$(sDate, "yyyy") _
         & " has " & sNumDays &" days."
   End Sub
				

The macro takes leap years into consideration when computing the number of days in February. For example, this routine divides the year by 4 and if the remainder is 0, there are 29 days in February of the year specified. Otherwise, there are 28 days in February of the year specified.

For additional information, please see the following article in the Microsoft Knowledge Base: