You can use the event Workbook_open, and use a macro like this:
Private Sub Workbook_Open()
Worksheets("sheet1").Range("A1").Value =
Worksheets("sheet1").Range("A1").Value + 1
End Sub

The code must be placed in the workbook code area, that can be accessed by
right click on the Excel icon left to the file menu and selecting "View code"

Hope this helps,
Miguel.

"john" wrote:

I have a template that I want a unique, sequential number
to appear every time the file is opened. Meaning, the first time it is

opened the number could be 101. The next time the template is used,
the file should open with 102 in the designated field and so on.

Any thoughts on how to accomplish this?