Key takeaways
What this article covers, in order:
- Why "just post it to sales" causes trouble later
- The simple case: one payment, one invoice
- One payment covering several invoices
- Part payments
- Overpayments
- Payments that arrive a few pounds short
Every payment a customer makes should be matched to the invoice (or invoices) it pays, not just posted as income. When one payment covers one invoice in full, that's easy. The fiddly cases are part payments, overpayments, one lump sum for several invoices and payments that arrive a little short. This post shows how to match invoice to payment in each case so your aged debtors report and your bank stay in agreement.
Why "just post it to sales" causes trouble later
Ellie runs a small catering company in Nottingham. For her first year she posted every deposit straight to sales income. Her P&L was roughly right. Her aged debtors report was a disaster: every invoice she'd ever sent was still showing as unpaid, totalling over £40,000, and she nearly chased a client for an invoice they'd paid in May 2026.
When a payment isn't matched to an invoice, the income is counted twice in effect: once when the invoice was raised and again when the cash landed. Either your sales are overstated or your debtors are, and usually both. Matching fixes that. The invoice gets marked paid, the debtor balance falls, and the cash goes into the bank account in your books.
The simple case: one payment, one invoice
A deposit of £850 arrives with the reference "INV-1038". There's an open invoice INV-1038 for £850. Match it. Done.
Most of your payments should look like this, and a good reconcile process should handle them in seconds. The rest of this post is about the ones that don't.
One payment covering several invoices
Bigger clients often pay in batches. On 2 Oct 2026, Ellie receives £3,150 from a corporate client with the reference "OCT PAYMENT RUN". Their remittance advice (the email or PDF telling her what the payment covers) lists three invoices:
| Invoice | Invoice total | Amount paid in this payment | Left to pay |
|---|---|---|---|
| INV-1041 | £1,200.00 | £1,200.00 | £0.00 |
| INV-1043 | £1,450.00 | £1,450.00 | £0.00 |
| INV-1046 | £900.00 | £500.00 | £400.00 |
| Total | £3,550.00 | £3,150.00 | £400.00 |
So one bank line is split across three invoices: two paid in full, one part-paid with £400 still owing. The invoice totals (£3,550) minus what was paid (£3,150) leaves exactly the £400 outstanding.
Tip: always ask for remittance advice from clients who pay in batches. Without it, you're guessing, and a wrong guess today becomes a confused phone call in three months.
If there's no remittance, the usual convention is to apply payment to the oldest invoices first. Then email the client to confirm. It takes two minutes and saves a lot of untangling.
Part payments
A customer pays £600 against a £1,000 invoice. Maybe they're paying in instalments, maybe they dispute part of it, maybe they've simply short-paid by mistake.
Bookkeeping-wise, it's straightforward: match the £600 to the invoice and leave it part-paid with £400 outstanding. Don't mark the invoice as paid and don't create a credit note for the £400 unless you've actually agreed to reduce what they owe.
What you need to find out is why. Then act on it:
- Agreed instalments: note the plan and the dates. Your aged debtors will show the balance ageing; that's fine.
- A dispute: sort it out. If you agree to a reduction, raise a credit note for the agreed amount so the invoice closes properly.
- A mistake: a polite email with the invoice and the balance due usually does it.
Overpayments
A customer pays £1,020 against a £1,000 invoice. It happens more than you'd think: a typo, paying an old amount, paying the gross when there was a discount.
Match £1,000 to the invoice. The extra £20 is money you owe the customer until it's dealt with, so it sits on their account as a credit (sometimes called an unallocated or on-account payment). Then either:
- Offset it against their next invoice, with their agreement, or
- Refund it by bank transfer and match the refund against the credit.
Never just post the extra to income. It isn't yours.
Payments that arrive a few pounds short
International clients often pay through a bank that takes a fee on the way. An invoice for £2,000 arrives as £1,985. Same with some payment platforms that deduct their charges before paying out.
If it's a bank or processing fee and your terms put those charges on you (or you've decided it's not worth arguing about), match the full £2,000 against the invoice and record the £15 as a bank charges expense. The invoice closes, the bank agrees, and the cost of getting paid sits where it belongs.
| What happened | Amount |
|---|---|
| Invoice total | £2,000.00 |
| Bank charges deducted on the way | £15.00 |
| Amount received in the bank | £1,985.00 |
£1,985.00 + £15.00 = £2,000.00, so the invoice is fully cleared.
If the shortfall is bigger than any plausible fee, treat it as a part payment and ask.
Payments with no clue who sent them
Every so often, £475 lands with a reference like "PAYMENT" and a name you don't recognise. Don't guess.
- Search open invoices for exactly £475.
- Check for invoices that would add up to £475.
- Look at the payer name in your bank's full transaction details; sometimes it's a director's personal account or a parent company.
- If nothing fits, post it temporarily to a suspense account and chase it down. Clear suspense before month end if you possibly can.
A weekly matching routine
- [ ] Reconcile the bank up to yesterday
- [ ] Match all one-to-one payments first (usually the bulk)
- [ ] Open any remittance advices and split batch payments
- [ ] Record bank fees on short payments
- [ ] Note part payments and send a quick query if you don't know why
- [ ] Put overpayments on account and decide: offset or refund
- [ ] Check suspense is empty, or nearly
- [ ] Run aged debtors and sanity-check it
Doing this weekly takes a quarter of an hour for most small businesses. Doing it once a quarter is a miserable afternoon.
How HelloBooks helps
Customer payments reach HelloBooks through your Open Banking bank feed (most UK banks and cards) or a CSV statement import, and land in a review list. On the reconcile screen, each bank line gets an AI match suggestion with a confidence score and a short reason why it picked that match, so the simple one-to-one payments go quickly and you only work through the exceptions left over. If a match is wrong, you can unmatch it in one click.
Invoices, AR ageing and payment reminders are on the Free plan, so your debtors report reflects what's actually been paid. See bank reconciliation software and automated bookkeeping for how it fits together.
FAQs
What is remittance advice?
It's a note from your customer, usually an email or PDF, telling you which invoices a payment covers. It's essential when one payment pays several invoices. If clients don't send one, ask; most finance teams can produce it automatically.
How do I record a customer overpayment?
Match the invoice amount to the invoice, then hold the extra as a credit on the customer's account. Either use it against a future invoice with the customer's agreement or refund it. Don't treat it as income.
Should I apply payments to the oldest invoice first?
It's a common convention when there's no remittance advice, and it keeps your aged debtors tidy. But a customer can choose which invoice they're paying, so if they tell you, follow their instruction.
What if the customer pays less because of bank charges?
If you're absorbing the charge, match the full invoice amount and record the difference as a bank charges expense. If your terms say the customer covers charges, you can ask for the shortfall, though for small amounts many businesses let it go.
Can I post a payment to suspense if I don't know what it's for?
Yes, temporarily. Suspense is a holding pen, not a home. Investigate quickly and move the amount to the right place, ideally before you close the month.
Match it right once and your debtors report starts telling the truth.
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