I need to enhance an invoice with an area for "balance over 30 days". It
should calculate this by comparing the current date to the date the service
is completed.

Since we e-mail these invoices to the district office for payment to the
sub-contractor's, the date sent is not an issue, only the date service is
completed. There are often invoices that have gone past 30 days, some 60 or
more days, and an invoice or billing statement that included this is what I
need. I've briefly looked in Access, & find nothing there, either.