Hi Beckwa
You could try this:
Right click a sheet tab, left click View Code.
In the VBA Project window at left select This Workbook.
Paste this code in the large white area
Private Sub Workbook_Open()
If Day(Date + 1) = 1 Then MsgBox "Last Day of Month"
End Sub
Above the code are 2 drop down boxes, in the left one select Workbook and in the right one select Open. Use Alt+F11 to return to sheet.
This message should display when you open the workbook on the last day of the month
regards
Derek