invoice number increments

Many ways, most involving cumbersome VBA of some kind.

The only way I've ever had success is to use a separate sheet to keep a LOG of the invoices I've created prior. If the log workbook had invoice numbers in column A, then you could use a standard worksheet formula like this to see the highest number used so far...and add 1 to that value:

=MAX('[Sample-1.xls]Sheet1'!$D:$D) + 1

When you complete each invoice, you just need to:

1) Save the invoice and convert the cell to a flat value so it doesn't change.
2) Record it in your LOG, too, so the next invoice template you open has the next number up