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Send a firm written reminder stating the invoice number, amount due, original due date, and a new pay-by date before you escalate. Keep the tone professional, cite any late-fee terms from your contract, and mail it certified so you have a paper trail. A past-due notice is a reminder, not a legal threat.
| Element | What to write |
|---|---|
| Statement of account | Invoice number, amount due, and the services or goods it covers |
| Original due date | The payment terms from the invoice (e.g. net 30) and the date payment was due |
| Late fees | Only what your contract or invoice terms actually allow |
| New pay-by date | A specific date, usually 10 to 15 days out |
| Next step if unpaid | Pause of services, referral to collections, or a formal demand letter |
| Your contact details | So the client can reach you to pay or dispute |
A past-due notice is the step before any legal language enters the picture. It says the account is overdue and asks for payment by a date. A demand letter says pay or face legal action. Skipping straight to threats over a routine late payment burns the relationship and can backfire if the client has a genuine dispute. Most unpaid invoices resolve at the past-due notice stage, which is exactly why the notice exists: it's cheaper and faster than every option that comes after it.
Firm and professional, never angry. The client may have missed the invoice, changed accounting systems, or be in a cash crunch. Write as though the delay is an oversight until proven otherwise, but make the seriousness unmistakable: state the exact amount, the exact date, and exactly what happens if the new date passes. One sentence near the end should note that continued non-payment will lead to the next step you name. That's enough; a physical letter on paper already carries more weight than the third email.
Only if your contract or written payment terms provide for them. Inventing late fees in the notice that were never agreed to will undermine your credibility and can be challenged. If your terms do allow them, state the rate or amount exactly as written in the contract and show the math for the balance as of the letter's date. If you have no late-fee clause, leave the subject alone and focus on the principal amount; the notice is about getting paid, not about penalties.
When your pay-by date passes with no payment and no response, the notice has done its job and it's time for the next step: a formal demand letter, pausing ongoing work, or engaging a collections process. Don't send a second identical notice hoping for a different result. Before escalating, check whether the client has raised any dispute about the work itself. If they have, resolve the dispute first, because a collections threat over a genuinely contested invoice creates problems you don't want.
Because every step after this one depends on proving you asked for payment clearly and the client ignored you. Certified mail with return receipt gives you a dated record of delivery that stands up in small claims court or in front of a collections agency. Keep copies of the invoice, the notice, the mailing receipt, and the return receipt card together. If the account ever goes to court, that folder is your case.
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