The short answer
A demand letter is the last thing you send before the dispute stops being between the 2 of you. It differs from every reminder that came before it in 3 ways: it states a total, it states a deadline, and it states what happens when the deadline passes.
Send it after the ordinary follow-ups and after you have paused work, rather than instead of them.
Put the whole claim in it: invoice numbers, dates, amounts, interest and costs.
Give a real deadline, usually 14 days, and a single way to respond.
Name the next step, and be willing to take it.
Send it in your own name, by a method that proves delivery.
Most demand letters work, which is the part people underestimate. A client who has absorbed 6 polite reminders often pays within a fortnight of a letter that reads as final, because it is the first message that changes what happens if they do nothing.
What makes it a demand letter
The follow-up emails that precede it ask for payment. A demand letter asserts a debt. The shift matters because the letter is written for 2 audiences at once: the client, and whoever reads it later if this ends up in front of a court, a collections agency or a lawyer.
That second audience is why the letter is worth doing properly even when you expect it to work on the first. A clear, dated, unemotional demand is evidence that you acted reasonably. A furious email at midnight is evidence of something else.
When to send it
After the ordinary sequence has failed and before you spend money. A workable order:
Reminders through the due date and the weeks after it, from your billing address.
A phone call, which is the step most often skipped and most often effective.
Written notice that work is pausing, per your suspension clause.
The demand letter.
Then, and only then, a lawyer's letter, a claim or a collections agency.
Sending it too early costs you the escalation. There is no rung above it that does not involve paying somebody, so a demand letter fired off at day 35 leaves you with nothing to do at day 90 except repeat yourself.
What it has to contain
Completeness is what makes it feel final. Anything missing invites a reply asking for it, which restarts the clock:
Your legal entity and theirs. The registered names, not the trading names.
What the debt is for, in 1 or 2 sentences, with the contract or purchase order reference.
Every invoice: number, date, due date and amount, itemised.
The total now claimed, including any interest and recovery costs you are entitled to.
What you have already done: the dates you invoiced, followed up and called.
A deadline, as a calendar date, typically 14 days from the letter.
The consequence, stated plainly and specifically.
How to pay, and 1 named person to reply to.
Where the client has raised an objection to the work, resolve the dispute before sending this. A demand letter over a contested amount is a poor document and a worse strategy.
The letter
Short, specific and unemotional. Every sentence either states a fact or states what happens next:
[Your company letterhead]
[Date]
[Client legal entity name]
[Registered address]
Re: Outstanding invoices totalling [amount]
Dear [Name],
I am writing about the following unpaid invoices, issued under our agreement dated [date]:
Invoice #214, dated [date], due [date]: [amount]
Invoice #221, dated [date], due [date]: [amount]
Total now outstanding: [amount]
These invoices relate to [description of work], which was delivered and accepted on [date]. No objection to the work or to the invoices has been raised.
We have requested payment on [dates] by email and spoke with [name] by telephone on [date], when we were told [what was said]. Payment has not been received.
We require payment of [amount] in full by [date, 14 days out]. Payment details are below.
If payment is not received by that date, we will [refer the matter to our solicitors / commence proceedings to recover the debt / instruct a collections agency] without further notice, and will seek interest and recovery costs where they are available to us.
If there is a reason for the delay that we are not aware of, contact me directly on [phone] before [date] and I will consider any proposal you wish to make.
Yours sincerely,
[Name]
[Title]
The penultimate paragraph is the one to keep. It costs nothing, it makes the letter reasonable rather than aggressive, and a client with a genuine cash problem will use it to propose a payment plan that gets you paid in full over a longer period.
Send it in your own name
There is a temptation to sound bigger than you are: a letter from an invented collections department, or a recovery firm that does not exist. In the US that temptation has a specific legal cost.
The Fair Debt Collection Practices Act regulates debt collectors, and the statutory text excludes an officer or employee of a creditor collecting the creditor's own debts in the creditor's name. Collecting your own invoice, under your own name, generally puts you outside the Act. The same definition, however, brings in any creditor who, in collecting their own debts, uses a name other than their own that would indicate a third person is doing the collecting.
So the fake collections letterhead is the one move that can convert an unregulated letter into a regulated one, with the restrictions and liabilities that follow. Several states also regulate original creditors more tightly than federal law does. Write as yourself.
The same logic applies to tone. Threats you will not carry out, implications about the client's reputation, or contact outside business hours all read badly later, whether or not a statute applies.
How to send it, and what to keep
Send it by email and by post on the same day, to the registered address and to a named individual. Where a signature on delivery is available, use it. The point is being able to say, later and precisely, that it arrived.
Keep the letter, the proof of delivery, the invoices, the delivery or acceptance record for the work, and the log of every earlier contact. That bundle is what a lawyer, a court or a collections agency will ask for first, and assembling it months afterwards from a sent folder is the part everyone regrets.
What happens next
Their response | What it means | What to do |
|---|---|---|
Payment | The usual outcome | Confirm receipt, then fix the terms for next time |
A payment proposal | Cash flow rather than refusal | Consider it, and put it in writing with dates |
A late dispute | Often a negotiating position | Deal with it on the merits, and pause the deadline |
Silence | The deadline is now the decision | Take the step you named, or lose the letter's force |
The last row is the one that matters. A demand letter whose deadline passes without consequence teaches the client that your deadlines are decorative, and no later letter from you will work as well.
If the client is in another EU country
There is a route built for exactly this. The European Order for Payment is a simplified procedure for cross-border monetary claims that the defendant does not contest, run on standard forms under Regulation 1896/2006. The court should issue the order within 30 days, the defendant then has 30 days to lodge a statement of opposition, and where none is lodged the order becomes enforceable in the relevant member state.
If the defendant does oppose it, the case moves into ordinary national proceedings, or into the European Small Claims Procedure for claims up to €5,000. That threshold is worth knowing before you start, since it shapes which route is proportionate. The setup questions behind cross-border invoices are covered in getting paid by a client in another country.
A note on England and Wales
A widely repeated claim is that a creditor must follow the Pre-Action Protocol for Debt Claims before suing. For most agency invoices that is wrong. The protocol itself states that it applies to a business claiming payment of a debt from an individual, and that it does not apply to business-to-business debts unless the party owing the money is a sole trader. Invoicing a limited company usually puts you outside it.
What does apply is the general Practice Direction on Pre-Action Conduct and Protocols, which expects parties to exchange enough information to understand each other's position and to consider settlement before issuing. A letter containing concise details of the claim, the facts, the sum sought and how it is calculated is what that comes down to, and the court can impose costs and interest consequences where a party has not complied. Which is, conveniently, a description of the letter above.
Your letter or a lawyer's
Your own letter first, in nearly every case. It costs nothing, it usually works, and it keeps the relationship recoverable. A solicitor's letter carries more weight and typically costs a few hundred dollars, which is worth spending once your own deadline has passed without a reply.
Going straight to a lawyer skips the cheapest effective step and makes the next conversation with that client harder than it needed to be. Going straight to a collections agency has the same problem with a larger fee attached, and the options are compared in the piece on collection services.
FAQ
How do I write a demand letter for an unpaid invoice?
State the parties by their legal names, list every invoice with dates and amounts, give the total claimed, summarise what you have already done to obtain payment, set a calendar deadline of about 14 days, and say exactly what you will do if it passes. Keep it factual and send it in your own name.
How long should I give them to pay?
14 days from the date of the letter is the usual period for a straightforward commercial debt, and it is long enough to be reasonable without being ignorable. Use a calendar date rather than a number of days, so there is nothing to interpret.
Do I need a lawyer to send one?
No. A demand letter from you carries legal weight as evidence of the claim and of your conduct. Instruct a lawyer once your own deadline has passed, because that is the point where the extra cost buys something you cannot supply yourself.
Can I add interest and costs to the amount I demand?
Where your contract provides for them, or where statute does, yes, and you should state the basis. Set them out as separate lines so the principal sum is unambiguous.
Is it risky to send a demand letter myself?
It is low risk when you collect your own debt in your own name and stick to facts. The main trap in the US is writing under an invented collections name, which can bring you inside the Fair Debt Collection Practices Act. Some states also regulate original creditors directly.
What if they dispute the invoice only after receiving the letter?
Treat the dispute on its merits, even though the timing is suspicious. Pause the deadline while you deal with it, resolve or narrow the disagreement, then resume from where you left off with the undisputed amount.
Not legal advice. Debt recovery procedure, interest entitlements and pre-action requirements differ by state and by country — have anything you intend to act on reviewed by your own lawyer.