How to Charge Late Fees on Invoices — Rates, Rules & Copy-Paste Wording

Chasing money is the worst part of working for yourself. A late fee won't fix a client who can't pay, but it reorders the pile for the client who just pays slowly. And slow pay is common: roughly half of all B2B invoices issued by North American businesses were overdue at any given time in Atradius's 2024 Payment Practices Barometer.

Here's how to pick a legal rate, word it so it sticks, and run the math without a spreadsheet.

Are late fees legal?

Yes. Late fees on invoices are legal in all 50 US states when two things are true: the client agreed to the fee in writing before the work started, and your rate stays under your state's usury cap. There's no federal cap on business-to-business late fees. State law and your contract do all the work.

The upfront part is where most freelancers trip. Courts treat a late fee as liquidated damages, meaning a pre-agreed, reasonable estimate of what slow payment costs you. Spring a fee on an invoice that's already late and you have a penalty, not an estimate. Courts throw those out. So the rate has to live in your contract, proposal, or signed terms before day one of the work.

"Agreed in writing" doesn't demand a formal contract. An accepted proposal, a signed estimate, or an email thread where the client says yes to your terms all count in most courts. The bar is proof the client saw the fee before the work, not a notarized document.

How much you can charge depends on your state: New York's default statutory rate is 9% per year (CPLR 5004), California's is 10% for written contracts (Civil Code 3289), and Texas defaults to 6% on open accounts that carry no agreed rate (Finance Code 302.002).

A signed contract lifts the ceiling in most states, commonly to 18% per year or more, and a few states set no cap at all on business-to-business deals. Texas is one. We don't know your state's current rules, and they do change, so check the statute or ask a local attorney before you pick a number. One more boundary: these are business-to-business rules. Invoicing consumers is a different animal, with tighter caps and disclosure laws, and this article doesn't cover it.

How much should you charge in late fees?

The standard for US freelance and small-business invoices is 1% to 1.5% per month on the unpaid balance, which works out to 12% to 18% per year. Of the two, 1.5% per month (18% APR) is the most common rate in business contracts, because it fits under most state caps and still stings enough to move you up the payment pile.

Push past 2% per month and you're in penalty territory, where judges start asking questions. Drop under 1% and the fee is too small to notice: on a $500 invoice, 1% is $5 a month.

Our default is 1.5% per month, prorated daily. Clients have seen that exact rate on utility bills and card statements for decades, so it never shocks anyone, and prorating keeps you honest when a client pays 17 days late instead of 30.

Flat fee vs percentage vs interest

Tiny invoices are the exception. A percentage of $200 is pocket change, so many businesses charge a flat fee of $25 to $50 instead. Some combine both: $25 flat plus 1.5% monthly covers small bills and big ones. Whatever you pick, keep it proportional to the invoice. A $50 fee on a $60 invoice reads as a punishment, and punishments are exactly what courts refuse to enforce.

State caps are written as annual rates, so if you think in months, multiply by 12 before you compare. Billing clients outside the US? The same logic applies, but the caps change country to country, and some hand you a default rate by law: the UK's Late Payment of Commercial Debts (Interest) Act 1998 sets statutory interest at 8% plus the Bank of England base rate on overdue business debts.

How do you calculate a late fee?

Multiply the unpaid balance by the rate, prorated for the time overdue. Say you issued a $1,000 invoice on net 30 terms with a 1% monthly late fee, and the client pays 45 days past the due date.

1. Start with the unpaid balance: $1,000.
2. Turn the monthly rate into a daily one: 1% / 30 = 0.0333% per day.
3. Multiply by the days late: 45 x 0.0333% = 1.5%.
4. Apply it to the balance: $1,000 x 1.5% = $15.00.

The fee is $15, and the new total due is $1,015. At 1.5% per month the same 45 days would cost $22.50. If your contract states an annual rate instead, divide by 365: $1,000 at 12% APR for 45 days comes to about $14.79.

Small numbers, and that's fine. The fee isn't revenue; it's a nudge with a paper trail, and it tells the client's accounts-payable team that your invoices carry a cost of delay. One fairness note on prorating: if a client pays 10 days late, charge for 10 days, not the whole month. Rounding up on a technicality is how a reasonable fee starts looking like a penalty.

Don't edit the original invoice when the fee lands. Send a new one (or a statement) with the fee as its own line, referencing the original invoice number, so their books and yours stay clean. If you'd rather skip the arithmetic, build the invoice in the free invoice generator and put the rate in the payment-terms line.

What should the late fee wording say?

Put the fee in writing in three places: the contract or proposal, the payment-terms line on every invoice, and the overdue email if it comes to that. Same rate everywhere. Here's wording you can copy.

The "whichever is less" tail matters: it keeps the clause enforceable even if your client's state caps you lower than the rate you picked.

Write the actual date, not a bare "net 30". "Due on receipt" gets ignored; "Payment due April 14, 2026" gets scheduled. More on term formats in invoice payment terms.

For the full escalation sequence, from the pre-due nudge to the final notice, steal from our past-due invoice email templates.

When do late fees kick in?

Whenever your terms say they do. Most small businesses give a grace period of 5 to 15 days after the due date before the fee starts, which covers genuinely slow bank transfers and lost emails without weakening the policy.

Two details to nail down in the wording: whether the fee accrues from the due date or from the end of the grace period, and whether partial months prorate. Accrue from the due date, prorate daily, and say both. Ambiguity is what turns a $12 fee into a week-long email thread. And if your client is a bigger company, your invoice is probably sitting in an AP portal like Bill.com or Coupa, where the person you email can't change anything. The fee line still matters there: it gives your champion inside the company a reason to escalate.

When should you waive a late fee?

Waive it for a good client's first slip, and never charge it on top of a genuine dispute. A late fee exists to fix payment habits, not to tax a relationship that's working.

If a client disputes the work in good faith, freeze the fee clock until it's settled. Stacking fees onto a contested invoice turns a fixable problem into a legal one, and it makes you look unreasonable in front of a judge if it ever gets that far.

And if the fee was never disclosed before the work started, don't charge it at all. That's the most common late-fee question our users ask, and the answer doesn't change: eat the delay this time, add the clause to your next contract, and move on. When you do waive a fee, do it in writing and do it once: "I'll waive it this time as a courtesy" keeps the policy alive for next time. Silent waivers teach clients the fee is decorative.

Charge the fee or waive it on purpose. The worst late-fee policy is the one nobody believes in, including you.

— Invvy house rule

Can you charge compound interest?

Sometimes, but we wouldn't. Compound interest on late fees is allowed in some states and restricted in others, it has to be spelled out in the contract, and it buys you very little at freelance invoice sizes.

Here's the difference on $1,000 at 1.5% per month. Simple interest adds $15 every month, so a 3-month delay costs $45. Compounded monthly, the effective annual rate climbs from 18% to about 19.6%, and that same delay costs roughly $45.68. You squeezed out 68 cents in exchange for wording that reads as predatory and draws scrutiny in the states that cap compounding. If you do compound, say so explicitly ("compounded monthly") and cap the total, because silent compounding is the version that gets fees thrown out. Simple interest, plainly stated. That's the whole play.

What do you need in place before charging a late fee?

• The late-fee clause is in your contract or proposal, signed before work starts
• A rate at or under your state's cap: 1.5% per month clears the bar in most states
• Every invoice repeats the rate and the exact due date in the payment-terms line
• Grace period of 5 to 15 days, stated in writing
• Daily proration, so partial months don't turn into arguments
• Your own rule for when you'll waive it, decided before you're annoyed

If late payment is a pattern rather than an exception, fees treat the symptom. Deposits, shorter terms, and a reminder cadence treat the cause: see how to get paid faster.