Which number to use in which situation
- Phoning a customer — the customer balance, with the invoice list to hand.
- Applying a payment — the specific invoice balances, oldest first unless told otherwise.
- Aging report — invoice level, because age belongs to the invoice.
- Credit decisions on new work — the customer balance and its age profile.
- Sending proof of payment — invoice level, via a receipt.
Why customers argue when you only quote one of them
"You owe us nine thousand" invites a challenge. "You have four open invoices — two are current, one is 34 days past due at $2,100, and one is disputed" invites a decision. The second version is only possible if the customer balance can be exploded into its invoices instantly.
This matters even more for commercial customers with multiple properties or projects. Their accounts payable team pays by invoice number and purchase order, not by relationship total.
Keeping both numbers honest
- Never store a customer balance as an editable field.
- Exclude drafts and cancelled invoices from both numbers, consistently.
- Show the oldest unpaid date and the last payment date next to the total.
- Keep credits visible in the balance rather than netted invisibly.