The short answer
A demand letter is a formal written request that a customer pay what they owe, or fix a problem, by a specific date before you take legal action. AI drafts one well from your invoice, contract and emails. It does not check the amount, the law in your state or whether suing makes sense; that stays with you or your lawyer.
We make Extra, an AI agent platform, so this article is written by an interested party. Facts about other tools and about the law come from the sources listed at the bottom, as of the date shown.
What is a demand letter for?
A demand letter puts a customer on formal notice that they owe you money (or must fix a problem), states exactly what you want and sets a final deadline before you take legal action. For a small business, it is the step between friendly reminders and small claims court.
It does two practical jobs. It often gets you paid: a clear, firm letter with a date and a consequence moves an invoice up the customer’s pile. And it builds your record: if you end up in court, it shows the judge you tried to resolve the dispute first, which small claims judges tend to look on favorably. Some states and courts even expect you to ask for payment before filing; check your local court’s rules.
A demand letter is not the first reminder. It comes after polite follow-ups (see our guide to chasing an unpaid invoice), when the tone has to change.
What should a demand letter for an unpaid invoice include?
An effective demand letter includes who you are, exactly what is owed and why, a clear deadline and what happens next, in a firm but professional tone.
- Your business details and the customer’s legal name and address.
- A clear subject line: “Final demand for payment, Invoice 1042.”
- The basis of the debt: invoice number and date, signed estimate or contract, the work delivered.
- The amount, itemized: principal, any late fee or interest your contract allows.
- Your earlier reminders, with dates.
- A specific deadline (10 to 14 days is common) and how to pay.
- The next step if unpaid: filing in small claims court, or sending the account to a collection agency or attorney.
Send it by a method that proves delivery: certified mail with return receipt, or email with a read receipt and a mailed copy. Keep a copy of everything.
What can you charge on top of the invoice?
You can charge late fees or interest only if your contract or invoice terms allowed them, within your state’s limits. Unlike some countries, there is no single federal late fee for business-to-business invoices in the US.
| Item | When you can claim it | Watch out |
|---|---|---|
| Principal | Always, if the work was delivered as agreed | Disputed work weakens the claim |
| Late fee or interest | If your signed terms set it | State usury and late fee limits apply |
| Collection costs | If your terms say the customer pays them | Courts read these clauses strictly |
| Court filing fees | Often recoverable if you win in small claims | Rules vary by state |
A good habit for next time: put the late fee and the collection cost clause on every estimate and invoice, so the demand letter only has to quote it.
When does small claims court make sense?
Small claims court makes sense when the amount is under your state’s limit, the debt is clear and you can show the paperwork. Limits vary a lot: in California, individuals can generally sue for up to $12,500, but businesses only up to $6,250, according to the California courts.
- Check your state’s limit and whether businesses have a lower cap.
- Check the deadline to sue (the statute of limitations), which varies by state and by type of contract.
- File where the customer is located or where the contract was performed, as your state’s rules allow.
- Bring the contract, invoice, proof of delivery, reminders and the demand letter.
Winning is not collecting. If the customer has no assets or has closed, a judgment may be hard to enforce. That is worth weighing before you file.
Do debt collection laws apply to your own demand letter?
Generally, no: creditors collecting their own debts are usually not “debt collectors” under the federal Fair Debt Collection Practices Act (FDCPA), and the FDCPA covers consumer debts, not business debts. But there are exceptions, and other rules still apply.
- If you collect under a different name that suggests a third party is involved, the FDCPA can apply to you.
- The FTC Act still bars unfair or deceptive collection practices by creditors not covered by the FDCPA.
- Many states have their own collection laws, some of which cover creditors.
- With consumers, never threaten action you do not intend to take, and never contact their employer or family about the debt.
In short: be accurate, be firm, do not bluff.
How do you write a demand letter with AI, step by step?
AI writes a good demand letter when you give it the documents and exact figures; it writes a bad one when you ask it to guess.
- Gather the documents: invoice, signed estimate or contract, emails, dates of reminders.
- Give the numbers: amount due, due date, the late fee your terms allow.
- Ask for a draft in a firm, courteous tone, with every item from the list above.
- Check every number and date, and recompute any interest yourself.
- Delete any statute it cites that you cannot verify.
- Send it with proof of delivery, and note the deadline in your calendar.
Common mistake: AI cites a statute that sounds right but does not exist in your state, or threatens remedies you cannot use. A letter that quotes a wrong law weakens your position. A plain letter with no citation is better than a wrong one.
When do you need a lawyer instead of AI?
Get a lawyer when the amount is large, the customer disputes the work, the contract is complex or the customer has filed for bankruptcy. AI helps you prepare a file; it does not weigh litigation risk.
- A dispute about quality, delays or defects.
- A customer in bankruptcy: claims have their own deadlines and rules.
- An amount above the small claims limit.
- A customer in another state or country.
How does Extra help with a demand letter?
Extra (hello-extra.com), the AI agent platform for small businesses, brings several agents to this job. Clara, the legal agent, reviews your contract to find the clauses that matter (late fees, deadlines, venue) and annotates your draft letter to flag what is missing, without presenting herself as a lawyer (see Clara). Oscar does the math on the figures you give him, and Pam drafts the cover email. Extra costs $99 per month for all eight agents (pricing).
When Extra is not the right fit: for a disputed or large claim, hire a lawyer. For a good customer who simply forgot, a phone call beats a certified letter.
Where should you start this week?
- List invoices more than 30 days overdue.
- Check that your terms state a late fee and who pays collection costs.
- Send a friendly reminder on any that have not had one.
- For the rest, draft a demand letter with AI, then check it.
- Put the deadline in your calendar and decide the next step in advance.
Read next: chasing an unpaid invoice, writing a contract with AI and reviewing a contract with AI.
Sources
- Judicial Branch of California, “Small claims in California,” accessed 11/06/2026
- Federal Trade Commission, “Think your company’s not covered by the FDCPA? You may want to think again,” 12/2015
- Consumer Financial Protection Bureau, “What laws limit what debt collectors can say or do?,” accessed 11/06/2026
- Consumer Financial Protection Bureau, “Fair Debt Collection Practices Act examination procedures,” 12/2022
