To write an overdue invoice letter, open with the invoice number, amount, and due date; state plainly that payment is overdue; reference the original terms; and set a firm new deadline. UK businesses can also add statutory interest, the Bank of England base rate plus 8%, and fixed compensation of £40 to £100 under the Late Payment of Commercial Debts (Interest) Act 1998. Escalate gradually: a friendly first reminder, a firmer follow-up, then a final notice before considering formal debt recovery.

Sending the same tone of letter on day 5 and day 55 undermines both. Use the overdue period itself to decide how firm the letter should be:

• Use a direct subject line. “Payment Reminder” is fine for a first letter; “Overdue Invoice, Payment Required” or “Final Notice” signals escalation for later ones.
• Lead with the essentials. The invoice number, date, amount, and original due date should appear in the first sentence or two; don’t bury them.
• State plainly that the payment is overdue. Avoid vague phrasing like “just checking in”; say directly that the invoice is now past due.
• Reference what’s already happened. From the second letter onwards, mention the date of the previous reminder so the client can see this is a pattern, not a one-off.
• State the amount now owed, including interest. Once statutory interest and compensation apply, show the original amount and the revised total separately so the client can see exactly how the figure was reached.
• Set a clear, dated deadline. “As soon as possible” invites delay; “by 14 August 2026” doesn’t.
• Give the client a way to flag a query. Some overdue payments stem from a genuine dispute or a missed invoice; inviting contact resolves these faster than escalating on a misunderstanding.
• Close with a professional, firm sign-off, and verify the postal address before you send. A letter returned as undeliverable resets the clock on your entire recovery timeline.

Under the Late Payment of Commercial Debts (Interest) Act 1998, a UK business is entitled to charge statutory interest on an overdue commercial invoice, even if this wasn’t mentioned in the original contract or invoice, provided the contract doesn’t already set an alternative rate. Statutory interest is simple interest, calculated as the Bank of England base rate plus 8 percentage points, and it starts accruing the day after the invoice becomes overdue. Because the base rate moves periodically, check gov.uk for the current figure before adding interest to an invoice rather than relying on a fixed number in a template.

On top of interest, businesses can also claim fixed compensation for the cost of chasing the debt, without needing to itemise those costs:

These rights apply to business-to-business debts and to invoices issued to public authorities, not to individual consumers, whose late fees are governed separately and must be reasonable rather than automatic.

Template 1: First Reminder (1–14 Days Overdue)

Subject: Payment Reminder, Invoice [Invoice Number]

Dear [Client Name],

I hope you’re well. This is a quick reminder that invoice [Invoice Number], dated [Invoice Date] for [Amount], was due for payment on [Due Date] and remains outstanding.

This may simply have been overlooked, so I’ve attached a copy of the invoice for your convenience. Could you arrange payment by [New Deadline]? If payment has already been sent, please disregard this note.

Please let me know if you have any questions about the invoice.

Kind regards,

[Your Name]

[Company Name]

Template 2: Firm Follow-Up (15–30 Days Overdue)

Subject: Overdue Invoice [Invoice Number], Payment Now Required

Dear [Client Name],

Our records show that invoice [Invoice Number] for [Amount], due on [Due Date], is now [X] days overdue. A first reminder was sent on [Date of First Reminder], and we have not yet received payment or a response.

Under the Late Payment of Commercial Debts (Interest) Act 1998, we are entitled to charge statutory interest at the Bank of England base rate plus 8%, together with fixed compensation, on overdue commercial invoices. We would prefer to resolve this without adding those costs, so please arrange payment in full by [New Deadline].

If there is a query holding up payment, please contact us immediately so we can resolve it.

Regards,

[Your Name]

[Company Name]

Template 3: Final Notice (31+ Days Overdue)

Subject: Final Notice, Invoice [Invoice Number] Overdue by [X] Days

Dear [Client Name],

Despite two previous reminders dated [Date] and [Date], invoice [Invoice Number] for [Original Amount] remains unpaid. As set out in our previous letter, statutory interest and fixed compensation now apply, bringing the total owed to [Revised Amount].

This is a final notice. If payment in full is not received by [Final Deadline], we will pass this matter to [a debt recovery agency / our solicitors] without further notice, which may result in additional recovery costs being added to the amount owed.

We would much rather resolve this directly. Please contact us immediately if you wish to discuss payment.

Yours sincerely,

[Your Name]

[Company Name]

Insurance: Brokers and insurers routinely chase overdue premium instalments and renewal payments. Because a lapsed policy has real consequences for the policyholder, these letters typically lead with the payment details and follow quickly with the risk of cover lapsing, rather than opening with a legal tone.

Healthcare: Private clinics and practices billing patients or insurers directly for treatment need a tone that stays courteous even at the final-notice stage, given the sensitivity of the relationship, while still being clear about the amount owed and the deadline for payment.

Finance: Lenders and asset finance providers chasing missed instalments on loans or leases often see statutory interest and compensation become material relatively quickly, since these amounts compound across a portfolio of overdue accounts rather than a single invoice.

SaaS and subscription billing: Recurring invoices that go unpaid are usually chased through an automated first-reminder email, with a printed letter reserved for accounts that reach the firm or final-notice stage, where a physical item tends to prompt a faster response than another email in a crowded inbox.

💡Also Read:Lease Non-Renewal Notice

• Vague subject lines that don’t signal urgency or make the letter easy to deprioritise.
• Leaving out the exact amount, invoice number, or deadline, which invites a query instead of a payment.
• Escalating to a legal or aggressive tone too early, before a client has had a fair chance to simply pay.
• Never verifying the client’s current postal address, so the letter is returned undelivered, and the overdue period keeps running unnoticed.
• Sending letters as one-off, manual tasks rather than a consistent, dated sequence, which weakens the paper trail if the debt is later escalated.

• Factor	Email	Standard Post	Tracked / Recorded Post
  Visibility	Easily lost in a full inbox or filtered as spam	Physical item, harder to ignore	Physical items signal seriousness
  Formality	Low, feels routine	Moderate, feels deliberate	High, feels like a formal step
  Proof of delivery	Read receipts are unreliable	None by default	Signed-for or tracked confirmation
  Best used for	Early, friendly reminders	Firm follow-ups	Final notices and pre-legal correspondence

   

  Getting the Operational Details Right

  The best-written overdue invoice letter still fails if it’s sent to the wrong address or never reaches the right desk. A few operational details are worth building into your process rather than handling ad hoc:

  • Verify the address before every mailing. PostGrid’s International Address Verification API checks and standardises UK addresses at the point of entry, reducing the number of letters returned as undeliverable.
  • Personalise each letter at scale. A merge-variable template editor lets you populate the invoice number, amount, and deadline automatically for every overdue account, rather than editing each letter by hand.
  • Automate the three-stage sequence. PostGrid’s Print & Mail API and Campaigns tools can schedule the friendly reminder, firm follow-up, and final notice to go out automatically as an account crosses each overdue threshold.
  • Confirm delivery. Tracking and Enhanced Reports give visibility into when a letter was sent and delivered, which matters if the debt is ever escalated and you need to show a documented paper trail.
  • Trigger letters from your existing systems. CRM and accounting integrations (including HubSpot, Salesforce, Zapier, and Make) can kick off a reminder letter automatically once an invoice is flagged as overdue, rather than relying on someone to remember to send it.