Customer Payment Plan: Track Instalments and the Balance

Start with one agreed balance

Before adding dates to a spreadsheet, reconcile the original invoice, receipts and credits. The plan's starting balance should be a figure both parties can identify. If the customer disputes part of it, resolve or separately document that issue before calling the entire amount agreed.

Keep the original invoice number, the plan reference, the agreement date and who accepted it. Record whether the agreed amounts include any fees or interest. Don't insert new terms because a template contains them: payment terms form part of the sales contract.

This example is for an already issued trade invoice paid over time. It isn't progress billing for work still to be delivered, a loan agreement or an ATO payment plan.

Separate scheduled payments from actual receipts

In the fictional example below, INV-517 has an agreed unpaid balance of $4,800. The parties agree to four $1,200 instalments. There are no fees, interest, discounts or further sales. The table shows a complete illustrative history, including dates after this guide's preparation date; these aren't actual customer payments.

Assumptions: AUD total cash amounts. Starting balance $4,800. Four agreed $1,200 instalments. The customer later agrees to catch up a $500 shortfall on 28 September; that change is preserved separately.

Agreed due date	Scheduled	Actual receipt	Remaining principal	Follow-up or evidence
14 Sep 2026	$1,200	$1,200 on 14 Sep	$3,600	Bank receipt R-201 matched to INV-517
21 Sep 2026	$1,200	$700 on 22 Sep	$2,900	Missed date; $500 still short. Follow-up logged 22 Sep.
28 Sep 2026	$1,200	$1,700 on 28 Sep	$1,200	Includes $500 catch-up agreed 23 Sep; R-219 allocated accordingly
5 Oct 2026	$1,200	$1,200 on 5 Oct	$0	R-224 matched; plan closed after reconciliation

Original ASBG fictional example. Use the assumptions above when replacing these figures with your own.

On 21 September, the second instalment is missing. The next day, $700 arrives. That leaves $500 of the second instalment unpaid and $2,900 outstanding across the whole plan. State both figures in the follow-up: $500 missed from that instalment and $2,900 left across the plan.

After the $1,700 receipt on 28 September, the overdue $500 and that day's $1,200 instalment are covered, following the documented allocation. The remaining principal is $1,200. Keep the original four dates visible even though the customer caught up later.

Set up a worksheet you can maintain

Use separate columns for due date, scheduled amount, receipt date, receipt amount, bank reference, allocation, remaining principal and action. Put agreed changes in a dated notes tab or linked document.

For an arrangement with no other adjustments:

Remaining principal = agreed starting balance − cumulative allocated receipts.

Shortfall to an agreed date = cumulative instalments scheduled by that date − receipts allocated to those instalments.

If receipts exceed the scheduled amount, investigate an advance payment or allocation issue; don't display a negative "overdue" figure as if it were a new credit decision. A genuine refund, fee or adjustment needs its own supported record.

In accounting software, match receipts to the original unpaid invoice. Don't create another sales invoice called "instalment 2" for the same work. Use a payment notice or schedule referencing INV-517. The bookkeeping guide covers the wider reconciliation routine.

Confirm the recorded arrangement

Use this as a record of what has actually been agreed, with the completed schedule attached:

Subject: Payment schedule for [invoice / plan reference]

Hello [name], this records the arrangement agreed on [date] for the unpaid balance of [amount] on [invoice reference], after receipts and credits up to [cut-off]. The attached schedule lists each instalment and date.

[List only changes both parties specifically agreed, with the relevant reference.] Please let us know if any detail differs from your understanding. Send each payment with [reference] so we can allocate it accurately. Our contact for questions about this record is [name and contact].

An administrative email shouldn't silently introduce a guarantee, default fee or a requirement to pay the whole balance immediately. Have any proposed legal change reviewed before adding it.

Keep reminders consistent with the agreement

Check automatic reminders against the agreed plan so they don't demand an amount already paid or contradict a recorded instalment date. Record the customer's communication preferences. Have your collection procedure checked against the agreement and the ACCC/ASIC guideline; the worksheet supplies no default fees, acceleration rights or new credit terms.

Use an internal reminder to check the bank. Keep that task separate from messages sent to the customer.

When an instalment is missed

Check the bank, reference and allocation first. Record the exact shortfall and ask the customer what happened. If a different date is agreed, save who agreed, when, which amount moved and whether later instalments changed. Retain the earlier schedule.

Before adding fees or escalating, check the agreement and obtain advice about what action is available. A missed-date flag is an administrative warning, not authority to change legal terms. Use the unpaid-invoice guide for background, with the agreement and current guidance controlling your response.

Feed confirmed receipts and remaining expected dates into the cash-flow forecast. More billing routines sit in cash flow and getting paid.

Next, check receipts, credits and report dates before chasing an old balance.

Key takeaways

• Reconcile and agree the opening balance before scheduling instalments.
• Keep scheduled dates, actual receipts and remaining principal separate.
• Preserve variations and match every receipt to the original invoice.
• Check the agreement before treating a missed payment as grounds for further action.

Where to get help

A commercial solicitor can review changes to terms and collection procedures; your bookkeeper can check receipt allocation. Refer to the ACCC/ASIC collection guideline and ASBFEO dispute support when an arrangement cannot be resolved directly.