How to write a demand letter for unpaid invoices
Updated 2026-06-20
You’ve sent friendly reminders. They’ve been ignored. Before you write the debt off or talk to anyone about legal action, there’s one formal step that often gets the money moving on its own: a demand letter — also called a final notice or letter before action.
When to send one
A demand letter is not your first move. Send it only after a normal reminder cadence has run its course — typically a friendly nudge, a firmer follow-up, then this. By now the invoice is well overdue and softer approaches haven’t worked.
Sending it too early reads as aggressive and damages the relationship for no reason. Sending it on time signals you’re organised and serious.
What a demand letter should include
- A clear statement that this is a formal demand for payment;
- The invoice number(s), original date(s) and amount(s) outstanding;
- Any late fees or interest you’re entitled to (see are late fees legal);
- A firm, specific deadline to pay (e.g. “within 7 days of this letter”);
- The consequences if the deadline passes — pausing work, recovery costs, or escalation;
- How to pay, so there’s no excuse left.
Get the tone right
Firm and factual, not emotional or threatening. State the facts, the amount, the deadline, and the consequence — nothing more. A calm letter that lays out exactly what happens next is far more effective than an angry one, and it holds up better if the matter ever does escalate.
Don’t bluff. Only state consequences you’re actually prepared to follow through on — empty threats train a client to ignore you.
Final notice vs. letter before action
These are rungs on the same ladder:
- Final notice / demand letter — your last direct request before escalating.
- Letter before action — a more formal step signalling legal proceedings may follow; in some places this has specific requirements, so for large or disputed sums it’s worth getting advice.
The demand letter generator produces a formal, professionally worded letter you can export to PDF, and the late fee & interest calculator works out any penalty to include. For the full escalation playbook, see what to do when a client won’t pay.
Better to never get here
A demand letter is a last resort — most overdue invoices never need one if they’re followed up early and consistently. Duefy chases on a schedule from the moment an invoice is late, so far fewer accounts ever reach the demand-letter stage.