Past Due Invoice Letter: Template and Wording

Twenty-one days after the due date, two polite reminders have gone unanswered and the invoice is still open. That is the point to send a past due invoice letter: a formal, written notice that sets out what is owed, how late it is and the date by which you expect payment. It is firmer than a reminder email but stops short of a demand letter, and it gives you a clean paper trail if you later need to escalate.

Below is a past due invoice letter template, a fully worked example with interest calculated, shorter wording options for email, and guidance on what to do next. This is general information, not legal advice; collection and interest rules vary by country and state.

Where the past due letter fits in your collection process

Stage	Typical timing	Document	Tone
1	Before and just after due date	Friendly payment reminder	Warm, assumes oversight
2	14 to 30 days overdue	Past due invoice letter	Formal, factual, firm
3	30 to 60 days overdue	Final notice before legal action	Serious, states consequences
4	After final deadline	Demand letter, collections or small claim	Legal

The timings are typical, not rules. A client who goes silent can move faster through the stages; a long-standing client with a temporary cash problem may need a payment plan instead. Our guide to handling an overdue invoice covers that judgment call.

What to include in a past due invoice letter

• Your business details and the date of the letter.
• The client's legal name and billing address, plus the named contact.
• A clear subject: "Past due notice: invoice INV-1042".
• Invoice number, issue date, original due date and amount.
• Days overdue, calculated from the due date.
• Payments already received, if any, and the balance remaining.
• Any interest or fees your terms or the law allow, with the calculation shown.
• A new deadline, usually 7 to 14 days from the letter date.
• Payment instructions and a reference to quote.
• An invitation to raise any dispute by a named contact, so a genuine problem surfaces now.
• Enclosures: a copy of the invoice and, for several open invoices, a statement of account.

Past due invoice letter template

[Your business name]
[Address] | [Email] | [Phone]

[Date]

[Client contact]
[Client legal name]
[Billing address]

Subject: Past due notice: invoice [number]

Dear [Name],

Our records show that invoice [number], issued on [issue date] for [amount], was due on [due date] and remains unpaid. It is now [number] days past due. We sent reminders on [dates] but have not received payment or a reply.

[Optional: Under [our terms / applicable law], interest of [rate] applies to overdue amounts. Interest to [date] is [amount], bringing the balance to [total].]

Please pay [total] by [new deadline] by [payment method], quoting [reference]. A copy of the invoice is enclosed.

If you believe this amount is incorrect, or if there is a reason payment has been delayed, please contact [name] at [email/phone] before [deadline] so we can resolve it.

If we do not receive payment or hear from you by [deadline], we will [next step, e.g. pause further work / issue a final notice].

Sincerely,
[Name, title]

Enclosure: Invoice [number]

Filled-in example with interest calculated

Here is the letter completed by a UK design studio billing a business client. The contract does not set its own interest rate, so statutory interest applies. Under GOV.UK guidance, businesses can claim interest on late commercial payments at 8% plus the Bank of England base rate (GOV.UK: charging interest), plus a fixed recovery sum set by the Late Payment of Commercial Debts (Interest) Act 1998, section 5A: 40 pounds for debts under 1,000, 70 pounds for 1,000 to 9,999.99, and 100 pounds for 10,000 or more.

For the example we assume a base rate of 4.00%, giving a statutory rate of 12.00% a year. Always use the reference rate that applies to your debt; our guide to statutory late payment interest explains how to find it.

Item	Calculation	Amount (GBP)
Invoice INV-1042 (issued 1 October, due 31 October)	Original amount	4,800.00
Payment received 5 November	Partial payment	-1,800.00
Balance outstanding	4,800.00 - 1,800.00	3,000.00
Daily interest	3,000.00 x 12% / 365	0.99
Interest 31 Oct to 21 Nov (21 days)	0.9863 x 21 (unrounded daily rate)	20.71
Fixed recovery sum	Debt between 1,000 and 9,999.99	70.00
Total now due	3,000.00 + 20.71 + 70.00	3,090.71

Dear Mr Hale,

Our records show that invoice INV-1042, issued on 1 October 2026 for GBP 4,800.00, was due on 31 October 2026. Thank you for your part payment of GBP 1,800.00 on 5 November. A balance of GBP 3,000.00 remains unpaid and is now 21 days past due. We sent reminders on 3 and 12 November.

Under the Late Payment of Commercial Debts (Interest) Act 1998, interest of GBP 20.71 has accrued to 21 November, and a fixed recovery sum of GBP 70.00 applies, bringing the total to GBP 3,090.71. Interest continues at GBP 0.99 per day until payment.

Please pay GBP 3,090.71 by 5 December 2026 by bank transfer, quoting INV-1042. If you believe any part of this is incorrect, contact me at accounts@studio.example before that date so we can resolve it. If we do not hear from you by then, we will issue a final notice.

Sincerely,
Clare Benson, Director

Shorter past due email wording

When a full letter feels heavy, these lines work in an email body with the invoice attached:

• "Invoice INV-1042 for USD 1,850.00 was due on 2 April and is now 18 days past due. Please arrange payment by 27 April or let me know if there is a problem."
• "Despite our reminders on 5 and 12 April, invoice INV-1042 remains unpaid. Please treat this as a formal past due notice and pay the balance of USD 1,850.00 by 27 April."
• "We value working with you, which is why I want to resolve invoice INV-1042 (USD 1,850.00, 18 days overdue) quickly. Can you confirm a payment date by Friday?"

How to send a past due letter, step by step

1. Reconcile first. Confirm no payment has arrived and check for partial payments or credit notes.
2. Check your terms. Find the agreed payment terms and any interest or late fee clause.
3. Calculate the balance, including any interest, and show the working.
4. Write the letter on letterhead using the template above.
5. Send it to both the contact and the accounts payable address, by email with a PDF, and by post if the amount is significant.
6. Diary the deadline and decide now what you will do if it passes.

If the client replies with a question about a line or an amount, answer it first using our templates for how to reply to an invoice query. If they say something on the invoice is wrong and refuse to pay, stop the clock and deal with the dispute; our guide to resolving an invoice dispute walks through it. If the invoice itself needs correcting, reissue it from our invoice generator and reference the original number.

Subject lines for a past due notice

The subject line should make the status clear without sounding hostile, because it is often all a busy approver reads:

• "Past due notice: invoice INV-1042, 21 days overdue"
• "Overdue balance of GBP 3,000.00: invoice INV-1042"
• "Action needed by 5 December: unpaid invoice INV-1042"
• "Second notice: invoices INV-1061 to INV-1063 past due"

Avoid capital letters, exclamation marks and words like "urgent" in the first formal notice. Save stronger wording for the final notice, where it signals a genuine change in approach.

Variations by situation

US clients: late fees and interest are governed by your agreement and state law, and many states cap rates. Only add a charge your contract supports. Debt collection laws aimed at third-party collectors typically do not apply to a business collecting its own invoices, but honest, non-threatening wording is always the right standard.

Consumers rather than businesses: the UK late payment act applies to business-to-business debts only. For individual customers, rely on what your contract says and keep the tone especially measured.

Ongoing work: say plainly whether work will pause. "Further deliveries will be scheduled once the balance is cleared" is clear without sounding punitive.

Mistakes to avoid

• Threatening action you will not take. It costs credibility at the next stage.
• Adding fees with no basis in the contract or the law.
• Getting the numbers wrong, especially after partial payments.
• Sending it only to someone who has left the client company.
• Ignoring a dispute and escalating anyway.
• Sharing the debt with third parties or on social media, which can create legal risk.

A clear original invoice makes every later letter easier to write. Create invoices with due dates, terms and late-payment notes in our free invoice generator, then download a PDF in seconds without signing up.