Can you charge interest on an overdue invoice?

Yes—in many cases you can charge interest or a late fee on an overdue invoice, but only to the extent the invoice or contract authorizes the charge and the rate and method comply with applicable state and federal law. The Consumer Financial Protection Bureau emphasizes that collecting any interest, fee or charge is unlawful unless it is "expressly authorized by the agreement creating the debt or permitted by law," so authorization and legal limits are the two central gates you must clear. (CFPB guidance compendium).

Below I explain the legal basics, the practical steps that protect you as a seller, and realistic examples that show where businesses commonly go wrong.

The two legal requirements: authorization and lawful rate

First, a fee or interest charge must be authorized. If your invoice or written contract says the buyer will pay interest or a specified late fee on overdue balances, that authorization usually satisfies the CFPB standard for consumer and collection situations. Without that written authorization, trying to tack on interest later creates legal risk. See the CFPB's statement that collectors should not collect any interest, fee, or incidental expense unless it is expressly authorized by contract or permitted by law (CFPB guidance compendium).

Second, the rate and structure must be lawful. States set usury rules and legal maximum rates, and those limits vary. For example, Virginia law provides a rule for open accounts allowing interest at the legal rate after a certain period, illustrating how state statutes can establish or restrict post-invoice interest. Consult the applicable state statute for the buyer's location; the Virginia statute is an example of a state rule you can review. (Va. Code § 6.2‑301).

Where the invoice involves consumer credit, federal rules such as Regulation Z (Truth in Lending Act) affect disclosures and what counts as a finance charge—so consumer invoices tied to credit may trigger additional obligations. See Regulation Z's discussion of finance charges and late fees for consumer accounts. (Regulation Z, 12 C.F.R. § 1026.4).

Practical choices: late fee vs. interest, simple vs. compound

You can choose a flat late fee or an interest rate. The law treats those options differently in some states. A flat late fee can be easier to justify and administer, but in certain jurisdictions it may still be counted when calculating whether a transaction exceeds a state's usury cap. Federal bank regulation guidance notes that late fees and interest are not always treated the same for state usury purposes, so check state law before relying on a particular characterization. (Comptroller of the Currency guidance).

Also decide whether interest will be simple (calculated only on principal) or compounded (interest on accumulated interest). Some states prohibit particular forms of compounding or retroactive rate increases unless the parties clearly agreed to them. A conservative practice is to specify simple interest and a clear start date for accrual.

How to draft invoice terms that hold up

1. Put the rate or fee in writing on the invoice or in the contract. The CFPB explicitly requires express authorization in the agreement creating the debt for any added charges; an invoice line that reads "Late payment interest: 1.5% per month, starting 30 days after invoice date" is far stronger than an oral promise.

2. Specify when interest begins, whether it is simple or compounded, and the calculation method (e.g., monthly on unpaid balance).

3. Use a modest, clearly disclosed rate that likely falls within state limits. Avoid surprise or punitive-sounding rates; courts and regulators scrutinize them.

4. If the buyer is a consumer, follow Regulation Z disclosure rules and CFPB guidance applicable to consumer credit arrangements (Regulation Z; CFPB guidance compendium).

A realistic example

Imagine a B2B supplier in Virginia issues an open-account invoice and its standard terms state: "Past-due balances accrue interest at the legal rate after 60 days." Because Virginia law includes an implied legal rate provision for open accounts, the supplier's terms align with state practice; the supplier should still confirm the actual legal rate and how it is calculated under state statute. See the Virginia statute for the rule that can apply to open-account invoices. (Va. Code § 6.2‑301).

Contrast that with a seller who secretly adds a 5% monthly interest charge to an invoice with no written notice. Without contract authorization and with a high effective annual rate, that practice risks violating state usury limits and the CFPB's prohibition on unauthorized collection of fees (CFPB guidance compendium).

What to do now: a short checklist for businesses and sellers

• Review written terms and invoices for express authorization of late interest or fees. If absent, add clear terms before extending more credit.
• Identify the governing law—usually the buyer's state or the contract's choice-of-law clause—and look up that state's usury and open-account rules (the Virginia statute and Texas statutes illustrate how state law can differ: Va. Code § 6.2‑301; Texas statutes).
• Prefer simple interest and modest rates; avoid retroactive hikes and unclear compounding.
• For consumer customers, follow Regulation Z disclosure requirements and CFPB guidance on authorized charges (Regulation Z; CFPB guidance compendium).

When to consult counsel and alternative steps

If the invoice is high-value, involves cross-state issues, the buyer disputes the debt, or you plan a high late rate, get legal advice. State-by-state usury details and consumer rules can create traps that lead to refunds, penalties, or other liabilities if mishandled. If the goal is to prompt payment rather than litigate, a clear written demand that states the amount owed, cites the invoice terms, and offers a short cure period often resolves matters; professionally prepared demand documents can help clarify your claim without suggesting litigation as the only option. For sellers who prefer professional help preparing such documents, can be a practical resource—note that BeforeSuit prepares documents from customer-provided information and is not a law firm.

Charging interest on overdue invoices is a useful tool when used lawfully. The two rules to remember are authorization in writing (or statutory permission) and compliance with the state's allowable rates and federal consumer rules. Follow clear invoice language, modest rates, and reasonable billing practices to reduce disputes and regulatory risk.

For help preparing a professional demand letter, BeforeSuit can help you prepare your next steps.