Unpaid Invoice Letter Template: What To Include

Chasing an unpaid invoice is frustrating, especially when you have already done the work, paid your staff or suppliers, and kept your side of the deal.

The good news is that a clear written demand can often get payment moving without the situation becoming a bigger dispute. It also helps protect your position if you later need to take more formal steps.

Below, we'll look at when a friendly reminder becomes a formal demand, what to include in an unpaid invoice letter, and when it's worth getting legal help with a letter before action.

Can I Send An Unpaid Invoice Letter In The UK?

Yes, you can send an unpaid invoice letter as soon as payment is overdue, unless your contract says you need to follow a specific process first.

For most UK businesses, your starting point is the customer contract, purchase order, statement of work, email trail or trading terms that set out when payment was due. If the due date has passed and the customer hasn't paid, you can write to ask for payment.

If there's no agreed payment date, business-to-business debts are often treated as late after 30 days under the Late Payment of Commercial Debts (Interest) Act 1998. That 30-day period usually runs from the later of:

• the customer receiving your invoice
• you delivering the goods or services
• the customer accepting the goods or services, if acceptance is part of the process

An unpaid invoice letter doesn't need to be aggressive. In fact, the best ones are usually calm, precise and easy to action. Your goal is to make it simple for the customer to pay, while making it clear that you're keeping a record and expect the matter to be resolved.

For example, Mike runs a small commercial cleaning business in Manchester. He completes a monthly office clean for a client and issues a £1,200 invoice with 14-day payment terms. The payment date passes with no response. Mike sends a polite overdue invoice email with the invoice attached, the due date, bank details and a request for payment within 7 days. That's a sensible first step before escalating.

When Does A Reminder Become A Formal Demand?

A reminder becomes a formal demand when you clearly state that payment is overdue, identify the amount owed, set a deadline for payment, and say what may happen if the customer doesn't pay.

There's no magic phrase that turns a reminder into a demand. It's more about the substance and tone of the communication.

Friendly Reminder

A friendly reminder is usually appropriate when the invoice has only just become overdue, or where you have a good relationship with the customer and suspect it may be an admin issue.

It might say that the invoice appears overdue, attach a copy, and ask the customer to confirm when payment will be made. This is often best sent by email.

Formal Demand

A formal demand is stronger. It should refer to the unpaid invoice, the contract or order, the due date, the amount outstanding and a clear deadline to pay.

You might use a formal demand where:

• your reminder has been ignored
• the invoice is significantly overdue
• the customer has promised payment but not followed through
• you're concerned about cash flow
• you want a clear paper trail before taking legal steps

Letter Before Action

A letter before action is the more formal step before making a court claim. It should be drafted carefully because it may later be reviewed if the dispute goes further.

For many unpaid business invoices, the court will expect you to have behaved reasonably before issuing a claim. Depending on who owes the money, this may involve the Practice Direction on Pre-Action Conduct and Protocols, or the Pre-Action Protocol for Debt Claims if you're claiming from an individual or sole trader.

If the customer is a limited company, a reasonable deadline is often around 14 days, depending on the circumstances. If the customer is an individual or sole trader and the Debt Claims Protocol applies, they generally have 30 days to respond using the reply form.

What Should An Unpaid Invoice Letter Include?

An unpaid invoice letter should include enough detail for the customer to understand the debt, check it internally, and pay without needing to ask follow-up questions.

Think of it as a practical document, not just a complaint. If your letter is vague, the customer may delay by saying they don't know what the invoice relates to. If it's too aggressive, it may damage the relationship or make the dispute harder to resolve.

A good unpaid invoice letter should usually include:

• Your business details: your legal business name, trading name, contact details and company number if relevant.
• The customer details: the correct legal name of the customer, not just a brand name or first name.
• Invoice details: the invoice number, invoice date, due date and amount outstanding.
• What the invoice relates to: a short description of the goods or services supplied.
• The legal or commercial basis for payment: the customer contract, quote, purchase order, trading terms or email agreement.
• Payment instructions: bank details, payment reference and any payment link if you use one.
• A deadline: a clear date by which payment must be made.
• Next steps: what you may do if payment isn't received, such as adding statutory interest, recovering fixed late payment compensation or sending a letter before action.

Keep your wording factual. For example, write Invoice 1048 for £1,200 was due on 15 March 2026 and remains unpaid, rather than you have deliberately refused to pay us. Unless you have clear evidence, stick to what you can prove.

It's also worth attaching the invoice again, plus any key document the customer may need to approve payment. The easier you make it to pay, the fewer excuses there are for delay.

Unpaid Invoice Letter Template: What To Include

A template can be a useful starting point, but it should be tailored before you send it, especially if the amount is large, the customer is disputing the work, or you may need to rely on the letter later.

Here is a practical outline you can adapt for your business. This isn't a finished legal document, and a legal professional should tailor it before you use it in a serious or disputed matter.

1. Subject Line: state that the invoice is overdue, using the invoice number and your business name.
2. Opening: address the customer by name and say you're writing about an overdue invoice.
3. Invoice Summary: list the invoice number, date, due date, amount due and what the invoice was for.
4. Basis For The Debt: refer to the contract, accepted quote, purchase order, email approval or trading terms.
5. Payment Request: ask for payment of the outstanding amount by a specific date.
6. Payment Details: include bank details, payment reference and who to contact if they need a copy invoice.
7. Interest And Charges: say whether you reserve the right to claim statutory interest and late payment compensation.
8. Dispute Window: ask the customer to tell you in writing by a set date if they dispute the invoice, and to explain why.
9. Next Steps: say that if payment or a valid response isn't received, you may escalate the matter, including sending a letter before action.
10. Sign-Off: include your name, role, business name and contact details.

For an overdue invoice email, the same structure works, but keep it shorter. Put the key details near the top and attach the invoice as a PDF. A simple subject line such as Overdue Invoice 1048 - Payment Requested By 22 March 2026 is clearer than something vague like payment issue.

If you're sending a final demand letter for an unpaid invoice, the tone should be more formal and the deadline should be clear. Avoid making threats you aren't prepared to follow through on. Say what you may do, not what you'll definitely do if you haven't yet decided.

How Do I Calculate Interest And Late Payment Charges?

You may be able to add statutory interest and fixed compensation to a business debt if your customer is another business and the debt is late.

Under the Late Payment of Commercial Debts (Interest) Act 1998, statutory interest is 8% a year plus the Bank of England base rate. The applicable base/reference rate can depend on when the debt became late, so check the current and relevant previous Bank of England base rates before calculating interest.

You may also be able to claim fixed late payment compensation based on the size of the debt:

• £40 for debts up to £999.99
• £70 for debts from £1,000 to £9,999.99
• £100 for debts of £10,000 or more

If your actual reasonable recovery costs are higher than the fixed compensation, you may be able to claim the difference as reasonable recovery costs. Whether that's sensible will depend on the amount owed and the documents you have.

Worked Example

Say Mike's cleaning business is owed £1,200 by a limited company customer. The invoice was due on 15 March 2026 and remains unpaid 60 days later. Because the debt is between businesses and is over £1,000 but under £10,000, Mike may be able to claim £70 fixed compensation.

He may also be able to claim statutory interest at 8% plus the Bank of England base rate. If the applicable base/reference rate for the relevant period were 4%, the annual rate would be 12%. On £1,200, that would be £144 per year, or about £23.67 for 60 days. Mike should check the current and relevant previous base rates before sending the demand.

Some customer contracts or credit terms have their own interest clause. If your contract has its own interest clause, check it carefully. A contractual interest clause may replace the statutory interest position, so don't assume you can claim both contractual interest and statutory interest.

When Should I Get Legal Help With A Letter Before Action?

You should consider legal help with a letter before action when the amount is significant, the customer is disputing the invoice, or you're close to starting a legal claim.

A letter before action isn't just a stronger reminder. It's usually the final written step before court action, so it needs to set out your claim properly and give the customer a fair chance to respond.

You may want legal help if:

• the customer says the goods or services were defective
• there are several invoices and payments to reconcile
• the customer is a sole trader or individual and the Debt Claims Protocol may apply
• you want to claim interest, compensation or recovery costs
• your contract has a dispute resolution clause you need to follow
• the amount owed is close to or above the small claims limit
• you're worried the customer may become insolvent

In England and Wales, many money claims for £10,000 or less are dealt with as small claims, though the route can depend on the type of claim and circumstances. That doesn't mean the pre-action stage is unimportant. A poorly drafted letter can make your claim look messy, or give the other side room to argue that you acted unreasonably.

A well-drafted letter before action will usually include the parties, the factual background, the legal basis of the claim, the amount claimed, interest and charges, key documents, the deadline for response, and what you intend to do if the matter isn't resolved.

Free templates can be fine for a low-value, straightforward reminder. An online fixed-fee legal service can work well where you want a properly tailored letter before action and cost certainty. A traditional hourly billing model may suit more complex disputes, but the cost can be harder to predict. Some providers quote a fixed fee up front if you want to compare that option.

Common Mistakes To Avoid

The biggest mistake is waiting too long without creating a clear written record.

Phone calls can help preserve relationships, but they're hard to prove later. If you speak to the customer, follow up by email with a short note confirming what was discussed and when payment is expected.

Other common mistakes include:

• Using the wrong customer name: check whether you contracted with a limited company, sole trader, partnership or another entity.
• Sending demands to the wrong address: use the agreed notice address, registered office, billing contact or email address in the contract where possible.
• Forgetting the invoice attachment: make it easy for the customer to process payment.
• Ignoring your own contract: your terms may require reminders, dispute meetings or notice in a particular form.
• Overstating your rights: only claim interest, compensation and costs where you have a proper basis to do so.
• Threatening action too early: a calm escalation path is usually more effective than an angry email.
• Continuing to supply without thinking: if the account is seriously overdue, check whether your contract lets you suspend services or stop new work.

Keep copies of every invoice, reminder, demand, delivery record, signed quote, purchase order, message and payment promise. If the matter escalates, those records help show that the debt is real and that you acted reasonably.

If the customer raises a genuine dispute, pause and assess it. Sometimes a credit note, partial payment plan or commercial settlement is better than spending more time chasing the full amount. The right move depends on the value of the invoice, your evidence and the relationship.

Key Takeaways

• You can send an unpaid invoice letter once payment is overdue, unless your contract sets a different process.
• A reminder becomes a formal demand when it clearly states the debt, the deadline for payment and the possible next steps.
• Your letter should include the invoice details, basis for payment, amount due, payment instructions and a clear response deadline.
• For business debts, you may be able to claim statutory interest at 8% plus the relevant Bank of England base/reference rate, and fixed compensation of £40, £70 or £100.
• Legal help with a letter before action is worth considering where the amount is significant, disputed or likely to escalate.
• Templates are useful starting points, but serious unpaid invoice letters work best when tailored to your contract and customer.

If you'd like help with your unpaid invoice demand letters, letter before action, payment terms or debt recovery process, you can reach us at 08081347754 or team@sprintlaw.co.uk for a free, no-obligations chat.