How to Charge Late Fees on Invoices Legally (US Guide + Global Notes)

Late fees on overdue invoices are legal in every US state, most provinces in Canada, and all of the UK, EU, and Australia. The rules vary by jurisdiction and by the nature of the debt, but the core principle is the same: if your payment terms are stated on the invoice at the time of delivery, and the late fee is reasonable, it’s enforceable.

This guide covers the US rules (with state-level caveats), the international rules, the exact wording to put on your invoice, and the four mistakes that make a late fee unenforceable. It’s not legal advice — it’s a practical overview for freelancers and small businesses. For edge cases, talk to an accountant or attorney.

The short version

• Up to 1.5% per month (≈18% annualized) is standard and enforceable in most US states without risk of usury
• State-specific caps apply in some states — California and New York tolerate up to 10% APR on judgments, but contract-based late fees up to 18% are typically fine
• The fee must be stated in writing on the invoice or contract before the debt becomes due
• The fee must be “reasonable” — not a punishment designed to be exorbitant
• International clients typically fall under separate legal frameworks (EU Late Payment Directive, UK statutory interest, etc.) which often give creditors rights that are stronger than US defaults

The number that works for most freelancers: 1.5% per month

1.5% per month = 18% annualized. That’s the de facto standard late fee rate for B2B invoices in the US and internationally. It’s enforceable in every US state without triggering usury concerns (which generally kick in above 20% APR for unsecured business debt). It’s common enough that clients rarely push back. And it’s large enough to actually motivate payment — at 1.5% monthly, a $5,000 invoice accrues $75/month in fees, which is a noticeable amount of money.

Why not higher? Courts scrutinize late fees that look punitive. A 5% monthly rate might survive in some states, but it also invites legal challenge — and a client who disputes a 5% late fee in court is a client who might get the entire fee thrown out, fee-waiving the debt. 1.5% is the sweet spot between “meaningful” and “obviously reasonable.”

Why not lower? 0.5% or 1% monthly sends the wrong signal. It reads as a symbolic gesture rather than an actual cost, and clients who read the terms correctly understand they can stretch payment almost indefinitely for a nominal penalty.

The exact wording for your invoice

Put this in the Payment Terms section of every invoice:

Payment Terms. Payment is due within 14 days of the invoice date (Net 14). A late fee of 1.5% per month (18% annualized) will be applied to any balance that remains unpaid after the due date. Late fees compound monthly. Payments must reference the invoice number.

Six sentences of work, legally enforceable in every US state. Let’s break down why each piece matters:

“Within 14 days of the invoice date” — establishes the start of the clock. Not “Net 14” alone, which could be ambiguous about when the 14 days begin.

“A late fee of 1.5% per month” — states the exact rate. Not “reasonable late fees may apply” which is unenforceable because it’s not a specific number.

“(18% annualized)” — pre-empts any claim that the rate was hidden or unclear.

“Any balance that remains unpaid after the due date” — unambiguous. Late fees apply from day 15 onward.

“Late fees compound monthly” — critical if the client goes 60+ days past due. Without this, some courts interpret the fee as simple interest, capping the total at the first month’s charge.

“Payments must reference the invoice number” — unrelated to the late fee but prevents partial-payment confusion later.

What makes a late fee unenforceable

Four mistakes that will cause a court (or a collections agency, or the client’s lawyer) to throw out a late fee:

1. It wasn’t stated on the invoice. You cannot invent a late fee after the debt is already overdue. The fee must be in writing on the original invoice, or in a signed contract the client agreed to before the work began. “I told them over email” is not good enough.

2. It’s above the state usury cap. Most states cap contractual interest at 10–20% APR for unsecured business debt. Some states (Alaska, Arizona, Arkansas, Texas) have stricter caps, and a late fee above that cap is partially or fully void. 1.5% monthly (18% APR) is safe in nearly all states. Avoid anything above 2% monthly unless you’ve confirmed it’s legal in your state.

3. It’s punitive rather than compensatory. Courts distinguish between “liquidated damages” (a reasonable estimate of what the lateness costs you) and “punitive damages” (a penalty designed to hurt). A $500 flat fee on a $100 invoice is punitive and unenforceable. A 1.5% monthly interest charge is compensatory and enforceable.

4. It was never actually applied. If you’ve let late fees slide for months or years without actually charging them, a court may interpret that as waiver — you gave up the right to enforce by not enforcing. Apply late fees consistently or accept that your late fee clause is decorative.

How to actually apply the late fee

Most invoice disputes happen at the “how do I add the late fee to the invoice” step, not at the legal question. The correct procedure:

1. Regenerate the invoice with a new line item: “Late fee (1.5% × $5,000 × 1 month): $75”
2. Update the total to reflect the new balance
3. Send the updated invoice as a new PDF to the client with a past-due notice email (see follow-up scripts for unpaid invoices)
4. Do NOT issue a separate invoice just for the late fee — keep it as a line on the original invoice so AP can process it as one item

The reason you update the same invoice rather than creating a second one: AP systems tie payments to invoice numbers, and a second invoice for a late fee creates a secondary record that can get paid separately from the original, leaving a balance neither side understands.

When should the late fee start accruing?

The cleanest policy is day 15 after a Net 14 invoice (or day 31 after Net 30). Not the due date itself — give the client one full grace day for same-day wire transfer processing and AP lag.

Some freelancers start the clock at day 1 after the due date. That’s legally fine, but it tends to annoy clients who genuinely paid on the due date but whose bank processed the wire overnight. A 1-day grace is generous without costing you anything meaningful.

At 14+ days past due, you move from “soft grace period” to “active late fee” and you apply the charge to the next invoice sent. More on the escalation path in the follow-up scripts guide.

Partial payments and late fees

When a client partially pays — say $3,000 on a $5,000 invoice — the late fee applies to the unpaid balance ($2,000), not the original total ($5,000). In writing:

Partial payments are applied first to outstanding principal, then to accrued late fees. Late fees continue to accrue on the unpaid balance until paid in full.

This language prevents the “I paid most of it, why am I still getting late fees” argument. Courts typically enforce it as written.

When NOT to charge a late fee

There are situations where charging a late fee is legally valid but strategically wrong:

• Long-term retainer clients who are 5 days late for the first time in 18 months — waive it, keep the relationship
• Enterprise clients on Net 60 stated terms when their AP cycle runs Net 70 — their policy, not your problem, charging a late fee will end the relationship without speeding payment
• Invoices under $500 where the fee would be under $10 — enforcement costs more than you’d recover
• Clients going through obvious financial distress who are actively communicating — late fees rarely motivate payment in this situation, they just accelerate the breakdown

The rule: late fees are a tool, not a reflex. Apply them when they’ll work. Waive them (with communication) when they won’t.

Outside the US

United Kingdom. The Late Payment of Commercial Debts (Interest) Act 1998 entitles you to charge statutory interest at 8% above the Bank of England base rate (approximately 13% as of April 2026) on any overdue B2B invoice, PLUS a fixed “debt recovery cost” of £40, £70, or £100 depending on the invoice size. You do NOT need to mention these in your terms — they apply by statute. But mentioning them explicitly on the invoice does speed up payment:

Late payments are subject to statutory interest and debt recovery costs under the Late Payment of Commercial Debts (Interest) Act 1998.

European Union. The EU Late Payment Directive 2011/7/EU entitles B2B creditors to 8% above the ECB reference rate in interest on overdue invoices, plus a minimum €40 compensation for recovery costs. These apply by default across all member states. Like the UK, you don’t need to state them to enforce them, but doing so on the invoice reduces dispute rates.

Australia. No federal late payment statute, but contract-based late fees are enforceable if stated on the invoice. 10% APR is common; anything above 15% is rarely enforced by courts without specific justification.

Canada. No federal statute. Contract-based late fees are enforceable if stated on the invoice, and up to 2% monthly (24% APR) is common practice. Small claims courts typically enforce reasonable rates without challenge.

Common myths about late fees

“You can’t charge late fees without a signed contract.” False. A clearly stated late fee on the invoice PDF is enforceable if the client accepted the work (by paying, or by not disputing before the work was delivered). A separate signed contract strengthens the case but isn’t required.

“Late fees above 10% are illegal.” Depends on the state. 1.5% monthly (18% APR) is enforceable in nearly all US states. Only a handful of states have stricter caps, and even those allow higher rates for commercial debt.

“If you don’t charge the late fee every time, you lose the right forever.” Depends on how long you ignore it. One or two waivers with communication don’t waive the right. Systematically ignoring the clause for months does.

“You can claim compound interest on top of the late fee.” Only if the invoice says so (“late fees compound monthly”). Without that language, most courts apply simple interest.

Ship the invoice with correct terms

Open the editor. The terms field defaults to Net 14 with a 1.5% monthly late fee — the rate that’s enforceable everywhere and gets paid fastest. Customize for your situation and download.