Demand letter for an unpaid invoice: template and when to send it

When to send a demand letter.

Send it when the email stages are exhausted: typically 30 to 45 days past due, after a friendly reminder, a past due notice and a final notice have gone unanswered. Sending it earlier rarely speeds payment and burns the relationship; sending it much later signals that you are not serious. A demand letter is not required by law in most states before you sue a business, but some courts expect one, some states require it in specific situations (New York’s commercial small claims part requires a demand letter before a claim against a consumer, according to the state court system’s small claims guide), and it is always evidence that you gave the debtor a fair chance to pay.

What the letter must include.

• The word “demand” in the subject line, so there is no doubt what the letter is.
• The total amount owed, and each invoice number, issue date, due date and amount behind it.
• What was delivered and when, in one line per invoice.
• The reminders you already sent, with dates.
• The late fee, if one was agreed, with a reference to the clause and the amount through the date of the letter.
• A firm deadline, usually 10 to 14 days from the date of the letter.
• The consequence if the deadline passes: a collection agency, a small claims filing, or referral to an attorney. Name one and mean it.
• Exactly how to pay: ACH details, a mailing address for checks, or a payment link.
• How to raise a dispute, in writing, by the same deadline.

How to send it.

Print it on letterhead, sign it, and send it by USPS Certified Mail with Return Receipt, which gives you proof of mailing and a delivery record with the recipient’s signature (as of October 2026, USPS lists Certified Mail at $5.55 plus $4.65 for a mailed return receipt or $2.91 for an electronic one, according to usps.com). Email a PDF copy the same day so the letter is read sooner; the certified mailing is your proof. Keep the signed letter, the mailing receipt, the return receipt and the email in one folder with the invoice, the contract and the reminders. If you later file in small claims court, that folder is your case.

Demand letter template.

[Your company]
[Address]
[Email and phone]

[Date]

VIA CERTIFIED MAIL, RETURN RECEIPT REQUESTED, AND EMAIL

[Client company]
Attn: [Name, title]
[Address]

Re: Demand for payment of invoice [number] in the amount of $[amount]

Dear [Name],

This letter is a formal demand for payment of the following overdue invoice(s):

Invoice [number], dated [issue date], due [due date], for [description of goods or services], in the amount of $[amount].
[Repeat for each invoice.]

My reminders of [date], [date] and [date] have gone unanswered. As of today the balance is [days] days past due.

[If a late fee was agreed: Under section [x] of our agreement dated [date], the overdue balance accrues a late fee of [rate]. The fee through today is $[fee], for a total due of $[total].]

Please pay the full amount of $[total] no later than [deadline, 10 to 14 days from the date of this letter]. Payment may be made by [ACH / check / card link]; the details are on the enclosed invoice.

If the full amount is not received by that date, I will [refer the account to a collection agency / file a claim in [county] small claims court / refer the matter to my attorney] without further notice, and I will seek all amounts the law allows, including court costs.

If you believe any part of this balance is not owed, reply in writing by [deadline] and state the reason. Otherwise I will treat the invoice as accepted and undisputed.

Sincerely,

[Signature]
[Your name]
[Title, company]

Enclosures: invoice [number]; agreement dated [date]; copies of reminders

What comes next if the deadline passes.

Collection agency

A commercial collection agency pursues the debt in its own name, with phone calls, letters and, if you authorize it, a lawsuit through its attorneys. Agencies commonly work on contingency: they keep a percentage of what they recover, and the percentage rises with the age of the debt and falls with its size. No recovery, no fee. Get the rate and the terms in writing before you place an account. Placing an account almost always ends the client relationship, so do it only when you have decided that is acceptable.

Small claims court

Small claims court is a simplified civil court for money claims up to a state-set limit, with low filing fees and no lawyer required. The limits differ by state and, in some states, by who is suing. Five examples, checked October 15, 2026, from official court sources:

The business-plaintiff rule matters: in California a company owed $9,000 must either waive the amount above $6,250 or file a regular civil case. You generally file in the county where the defendant lives or does business, pay a filing fee, and serve the defendant. A judgment is not money; you still have to collect it, and the court’s enforcement tools, such as bank levies and wage garnishment, make that possible but not automatic.

Attorney demand letter

For larger balances, a letter on a law firm’s letterhead often gets the response yours did not, because it signals that litigation is funded and ready. Many business attorneys write one for a flat fee; ask before you engage. For balances above your state’s small claims limit, the attorney can also tell you whether a regular civil suit is worth its cost, which depends on the amount, the evidence and whether the debtor can pay a judgment.

Have the file ready before you need it.

By the time you write a demand letter you need dates: when the invoice went out, when each reminder was sent, whether it was delivered, and whether the client answered. Dunlio keeps that history per invoice, with the three reminder stages, their send dates and their delivery status in one place, so the “my reminders of” line in the letter writes itself. Dunlio does not send letters, file claims or collect payments. The three reminder email templates and the late fee rules are in our guides.