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>You get the balance by adding up the unpaid amounts for the invoices. I sure hope I don't get a bill and make a payment and not see it wipe out my oldest balance. You have two choices of accounting approaches here, open balance which you said you want, and open item which requires that each invoice have payments applied to it manually, meaning someone has to distribute the payment to specific invoices.
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>As for tracking overages, you can add a new invoice with a CM in front of its ID and give it a negative balance equal to the amount left over. That is called a Credit Memo and it is the standard accounting way of handling over payments.

Ok, the light went on about calculating balances as I was typing the other message. My thinking got stuck in figuring the balance from a recorded amount and I missed the obvious bit of subtracting the paid amount from the original amount on each trip.

Unfortunately, some clients _want_ the payments to be applied to a particular aged balance, so I have to deal with that possibility.

I don't want the user to have to distribute the payments. It'll just take a bit of programming to determine which trips to apply it to. I think I can handle that. (That is, until I actually try it. :)

Ok, (deep breath) I'm making progress. Now this credit memo business... I put an invoice with a negative balance. How/When does this get applied to the trips?

Thanks,

-Michelle