Demand Letter Generator for Unpaid Invoices

Turn an overdue invoice into a formal, dated demand for payment — with the interest computed for you and, if no rate was ever agreed, your state's statutory default rate cited to the controlling statute (from the same verified 51-jurisdiction table as our late fee calculator). Everything runs in your browser, and this page does not send what you type. Figures passed from the late-fee calculator are in this page's web address (URL), which your browser sends to our server when it loads the page and which this page's Google Analytics tag reports as the page URL.

Not legal advice. This assembles a letter from your inputs and public statutes — it is general information. For significant or disputed amounts, have a licensed attorney review before sending.

1. The parties

2. The invoice

3. The interest

The rate stated in your contract or on the invoice.

4. The demand

How the interest is computed

Simple interest: interest = amount × (APR ÷ 365) × days overdue

Days overdue are counted from the invoice due date to today. The same formula (and the same verified state table) powers our late fee calculator — start there if you only need the number, come here when you need the letter.

Where the statutory rates come from

When you pick “use my state's statutory default”, the rate, the statute citation, and (optionally) the verbatim statutory text come from our 51-jurisdiction reference table — every row individually verified against the primary source with the verification date shown, and re-checked on a published schedule (changelog). States that set the rate by formula or periodic order link the official current-rate page instead of a frozen number.

Demand letter or final-demand invoice?

Short answer: send a demand letter when you need one formal document that sets out the debt, the interest and its basis, and a payment deadline. Re-send the invoice itself, marked as a final demand, when the client only needs the same invoice again to pay against. You can also do both: send the letter with the invoice attached.

When a demand letter fits

  • Your reminders have gone unanswered and you want a dated, formal record of the demand.
  • You are claiming interest and want the rate and its basis (your contract, or your state's statute) stated in writing.
  • You want to set a deadline and say what happens if it passes.

When re-sending the invoice fits

  • The client has not disputed the invoice, and their accounts team pays against invoice documents.
  • You want the amount due, the original invoice number and the due date on one page they can process as it is.

How to re-send the invoice as a final demand

  1. Choose the generator. The PDF from the free invoice generator on our home page always prints the heading "INVOICE". To print your own heading, use a generator whose template prints the Document Title field, such as the freelance invoice generator.
  2. Load or re-enter the original. Each generator keeps your last draft in this browser, so if you made the original invoice in that generator on this device, it reloads when you open the page. Otherwise, re-enter the original invoice.
  3. Keep what identifies the debt: the original invoice number, invoice date, line items and due date, so the document reads as the same invoice, not a new charge.
  4. Replace the editor's sample content. A new draft opens with sample values: replace the placeholder business and client details, payment details, line items, notes and terms, and set the tax label and rate to what the original invoice showed (rate 0 if it charged none). In the freelance generator, also set Deposit Paid to what the client has actually paid (0 if nothing).
  5. Change the Document Title (up to 100 characters) to, for example, "FINAL DEMAND — INVOICE". Leave Document Type on Invoice, because choosing a type rewrites the title. On the home page generator, where the heading stays "INVOICE", put the final-demand wording and the new deadline in the Notes field instead.
  6. Add interest only if you are entitled to it. If your contract or your state's rule allows it, add the interest computed on this page as its own line item, for example "Late-payment interest: [rate]% a year, simple, [days] days from [due date]", quantity 1. A percentage tax rate and any discount set in the editor apply to every line, including this one, so check the tax and the total before you download. The state table in the late fee calculator links a page for each state with its statute.

For the covering email, adapt the "Final Notice" script in our invoice payment terms guide.

Demand Letter FAQ

Is this letter legal advice?

No. This tool assembles a letter from your inputs plus the statutory citations in our verified state table. It is general information, not legal advice, and no attorney-client relationship is created. For significant amounts, disputed debts, or anything already in litigation, have a licensed attorney in your state review before sending.

How is the interest figure calculated?

Simple interest: amount × (annual rate ÷ 365) × days overdue — the same formula as our late fee calculator. If your contract or invoice states a rate, use that rate. If nothing was agreed, most US states supply a statutory default rate; pick your state and the letter cites the controlling statute for it.

Can I demand interest if my contract never mentioned late fees?

In most US states, yes — a statutory default interest rate applies to overdue commercial debts even when the contract is silent, and that is exactly the rate this tool inserts, with the statute cited. The details (when interest starts, what rate) vary by state: check your state's row in our late fee table, and verify against the linked official source.

How should I send a demand letter?

Common practice is to send it in a way you can later prove: email with delivery/read confirmation, plus a mailed copy via a tracked or certified service where available. Keep a copy of the letter, the original invoice, and the delivery evidence together. If the deadline passes without payment, your options depend on the amount and your jurisdiction — small-claims court thresholds and procedures vary.