What is a standard late fee for an invoice?

1.5% per month on the outstanding balance — 18% per year — is the most widely used commercial figure, and rates from 1% to 2% per month are all common. What matters more than the number is that it appeared in the terms your client agreed to before the work started.

How do I calculate a 1.5% monthly late fee?

Multiply the overdue balance by 0.015 for one month of interest, then pro-rate for the actual days late: balance × 0.015 × (days ÷ 30). A $2,000 invoice 45 days late is $2,000 × 0.015 × 1.5 = $45.

Can I charge a late fee if it was not in my contract?

Generally no. A fee you never disclosed is hard to enforce and costs you goodwill for a small sum. Send a firm reminder for the original amount, then add a late-payment clause to your contract, quote and invoice template so the next one is covered.

Is there a legal limit on invoice late fees?

Yes. Maximum interest rates are set by state or national usury law and vary widely, and consumer balances are usually capped more tightly than business-to-business debt. An agreed rate can still be unenforceable if it exceeds the local ceiling.

Should late interest be simple or compound?

Simple interest — charged only on the original overdue amount — is the norm for commercial invoices. Compound interest charges on the balance including previously added fees, so it grows faster, and it generally applies only if your contract says so explicitly.

Is a late fee or pausing work more effective?

For one-off project work, a fee. For retainers and ongoing engagements, pausing work is far stronger — a client who has not noticed a $30 charge will notice their site going unmaintained. Say in your terms that work pauses on overdue accounts, then actually pause it.

Do late fees apply to the invoice total or the unpaid balance?

The unpaid balance. If a partial payment was made, interest accrues on what remains rather than the original total — charging on the full amount after a part-payment is the error most likely to get your fee disputed.

How to Charge Late Fees on Invoices

Published September 1, 2026

A late fee is the only lever on an unpaid invoice that costs you nothing to pull. It works less through the money it collects than through the queue it changes: when a client sits down with a stack of invoices and one of them is quietly getting more expensive, that one gets paid first. The mechanics are simple arithmetic. The part that decides whether you actually collect is the paperwork you did before the work started.

This guide covers all three pieces — the rate to charge, the clause that makes it enforceable, and the escalation sequence that turns an accruing balance into a payment — then points at the calculators that produce the figures you will quote.

The short answer

The standard commercial invoice late fee is 1.5% per month on the outstanding balance, which is 18% per year. Pro-rate it for the actual days late: balance × 0.015 × (days ÷ 30). On a $10,000 invoice 30 days overdue that is $150. The fee is only enforceable if the client agreed to it before the work began.

Pick a rate, then pro-rate it

Nearly every commercial late-fee clause is written one of two ways: a monthly percentage, or an annual percentage that is divided down. 1.5% per month — 18% a year — is the convention, and it is high enough to matter without reading as punitive. Rates between 1% and 2% per month are all unremarkable to a client's accounts payable department.

The arithmetic that trips people up is the pro-rating. A monthly rate does not mean you charge nothing until day 30 and a full month's interest on day 31. Multiply the balance by the monthly rate, then scale by the actual days: balance × rate × (days ÷ 30).

Fee on a $10,000 overdue invoice at 1.5% per month
Days late	Late fee	Total due	Cost per further day
15	$75.00	$10,075.00	$5.00
30	$150.00	$10,150.00	$5.00
45	$225.00	$10,225.00	$5.00
60	$300.00	$10,300.00	$5.00
90	$450.00	$10,450.00	$5.00

Simple interest, no grace period. The per-day figure is the number worth quoting in a reminder — it turns an abstract balance into a running meter.

Flat fee, percentage, or both

A percentage scales fairly but lands softly on small invoices: 1.5% of a $300 job is $4.50, which changes nobody's behaviour. A flat fee lands hard on small invoices and looks absurd on large ones. The structure should follow your invoice sizes rather than a template's default.

Choosing a late-fee structure
Structure	Typical level	Best suited to
Monthly percentage	1% to 2% per month	Invoices over roughly $500, and ongoing client relationships
Flat fee per missed deadline	$25 to $50	Small invoices of similar size, where a percentage is too small to notice
Flat fee then interest	$25 up front, then 1.5%/month	Clients with a history of paying very late
Suspension of work	No fee — work pauses	Retainers and ongoing engagements, where leverage beats interest

Above 2% per month a rate starts to read as punitive, and may exceed what local law allows on a commercial debt.

The clause is what makes the fee collectable

A late fee is a contract term, not a right. Charged without prior agreement it is very hard to enforce and it damages the relationship for a small sum — which is why the answer to "can I add a late fee to an invoice that is already overdue?" is almost always no, and the productive move is to fix the template for next time.

Three placements do the work. Put the clause in the contract or signed proposal the client accepted; repeat it on every invoice, including the ones paid on time; and state it in the payment terms line rather than burying it in a footer. A fee that has been printed on eight previous invoices reads as policy. One that appears for the first time when it is charged reads as a penalty.

Name the rate and the basis: "1.5% per month (18% per annum) on balances over 30 days past due."
State when the clock starts — on the invoice date, the due date, or after a stated grace period.
Say whether interest is simple or compound. Simple is the commercial norm; if you do not say, assume you will have to argue for compound.
Address a person, not a department. Invoices addressed to nobody in particular are the ones that sit.
Keep the fee inside your jurisdiction's usury cap — an agreed rate can still be unenforceable if it is too high.

When the law sets a better rate than your contract

In two situations the statutory rate can beat whatever your contract says, and the entitlement does not depend on having a late-fee clause at all.

Construction is the clearest case. Most US states, and the federal government on its own contracts, have prompt-payment legislation setting deadlines for paying contractors and subcontractors along with the interest that applies when the deadline is missed. Public projects usually carry shorter deadlines and clearer interest entitlements than private ones. Where a statute applies, check it before you invoice for interest, because the contract rate may be the lower of the two.

The mirror case is consumer debt. Late fees on amounts owed by individuals — patient balances, consumer accounts — are regulated far more tightly than business-to-business interest, and some jurisdictions cap them specifically. A rate that is unremarkable between two companies can be unlawful against a consumer.

Commercial B2B: your contract rate governs, subject to the usury cap.
Construction: compare your contract rate against the applicable prompt-payment rate and use the higher one. Lien and bond deadlines are separate, strict, and usually stronger leverage than interest.
Consumer balances: assume tighter caps and specific disclosure rules apply, and check before charging anything.
Cross-border work: the client's jurisdiction may impose a statutory right to interest on commercial debt regardless of your terms.

Escalate on a schedule, not by mood

Collection works when it is boring and predictable. Decide the sequence once, apply it to every client, and let the dates do the confrontation for you.

A workable escalation sequence
Days past due	Action	Tone
3	Short reminder, original amount, no fee mentioned	Assume an oversight
14	Formal reminder showing the accrued fee and the new balance	Factual
30	Final notice with a payment deadline and next step named	Firm
45	Decide: payment plan, small-claims filing, or collections	Decisive

Offering to waive the accrued fee in exchange for immediate payment converts the fee into a discount for paying now — which is usually what you wanted. You keep the client and the cash, and the fee has done its job.

Run the numbers

The calculators that apply everything above, with the same figures behind them.

Invoice Late Fee Calculator

The exact fee, new balance and per-day accrual for your rate and days late.

Late fees for freelancers

Realistic freelance rates and the wording to charge without losing the client.

Late fees for contractors

Prompt-payment statutes, retainage and lien rights as leverage.

Refund Policy Generator

The other half of your terms — refunds, deposits and cancellations.

Frequently asked questions

What is a standard late fee for an invoice?: 1.5% per month on the outstanding balance — 18% per year — is the most widely used commercial figure, and rates from 1% to 2% per month are all common. What matters more than the number is that it appeared in the terms your client agreed to before the work started.
How do I calculate a 1.5% monthly late fee?: Multiply the overdue balance by 0.015 for one month of interest, then pro-rate for the actual days late: balance × 0.015 × (days ÷ 30). A $2,000 invoice 45 days late is $2,000 × 0.015 × 1.5 = $45.
Can I charge a late fee if it was not in my contract?: Generally no. A fee you never disclosed is hard to enforce and costs you goodwill for a small sum. Send a firm reminder for the original amount, then add a late-payment clause to your contract, quote and invoice template so the next one is covered.
Is there a legal limit on invoice late fees?: Yes. Maximum interest rates are set by state or national usury law and vary widely, and consumer balances are usually capped more tightly than business-to-business debt. An agreed rate can still be unenforceable if it exceeds the local ceiling.
Should late interest be simple or compound?: Simple interest — charged only on the original overdue amount — is the norm for commercial invoices. Compound interest charges on the balance including previously added fees, so it grows faster, and it generally applies only if your contract says so explicitly.
Is a late fee or pausing work more effective?: For one-off project work, a fee. For retainers and ongoing engagements, pausing work is far stronger — a client who has not noticed a $30 charge will notice their site going unmaintained. Say in your terms that work pauses on overdue accounts, then actually pause it.
Do late fees apply to the invoice total or the unpaid balance?: The unpaid balance. If a partial payment was made, interest accrues on what remains rather than the original total — charging on the full amount after a part-payment is the error most likely to get your fee disputed.

Sources

State usury statutes: Maximum contract interest rates, with separate commercial and consumer ceilings in most states.
State and federal prompt-payment acts: Payment deadlines and statutory interest for construction work, including the federal Prompt Payment Act for government contracts.

General information only, not financial, tax or legal advice. Rates and rules vary by jurisdiction and change over time — verify anything consequential with a qualified professional. See our disclaimer.