Once the month ends, cell "A1" must tick over to zero, where "A1" is used by me as a counter to show how much has been deliverd to date for the month.

Basically, you need to detect when the month rolls over.

1. Unless the program is running all of the time (is it?), this can be tough to do. I'd suggest that whenever the program (Excel) terminates, you write a VBA routine that writes the current date and time to a disk file. If you open the program again, another VBA startup routine should look for the file. If it exists, the program can read the file and determine if the month has rolled over. If it has, it sets the appropriate cell to zero.

2. While the program is running, you need to start an event that will trigger periodically. Excel has an "OnTime" function that you can use to do that. This is described in this article.

Pearson Software Consulting

The article also shows you how to use Windows Timers, if you wish to do that. For your application, you'll probably be best served using the OnTime function. I'd probably set it up to run once an hour, if I were you.

In your subroutine -- the one that's invoked by the OnTime event, you'll have to determine the current month and compare it with the last month that you saved. You can do this as follows:

Dim CurrentMonth as integer
Dim NewMonth as integer

Private Sub DetermineMonth
NewMonth = Month(Now)
If NewMonth <> CurrentMonth then
Cells(Range("A1")) = 0 ' use this
Cells(1,1) = 0 ' or this
' or any other way of assigning a value to a cell.
CurrentMonth = NewMonth ' be sure and assign the CurrentMonth to the current month.
End If
End Sub

Thank you,
Did get around the problem using a hiden (Month) formula.
ie: NOW() - (Month)<>0 = set value to 0.