The hard rule: the fee has to be on the invoice before it goes out
The thing that catches most operators is this. You finish the work. You send the invoice on Friday. The customer sits on it for forty days. You are mad. You sit down to send a reminder and you type "and a 1.5% monthly late fee will be added." That late fee is not collectible. The customer never agreed to it. Their original document says nothing about it. Their accounts payable, if they have one, will pay the original total and ignore the new line.
Every authoritative legal source on this agrees on the same rule. To charge a late fee, the fee has to be disclosed in writing before the invoice becomes overdue. Either it is in a signed contract or service agreement, or it is on the original invoice itself in a payment-terms line. After the fact, the customer is not obligated to pay it, and most state courts will not enforce it.1
That is also why the invoice itself is the cleanest place to put the fee, even when there is a separate signed agreement. A contract in a folder somewhere is easy to argue about. A line at the bottom of the invoice that reads "Payment due in 30 days. Past due invoices are subject to a 1.5% per month finance charge" is hard to argue about, because the customer has it in their hand the day the work is done.
If you are reading this with an overdue invoice in front of you that has no late-fee language on it, the practical answer is not to invent one now. The practical answer is to update the template, get the next invoice out the door with terms that hold up, and use the reminder cadence in our guide to invoice reminders on the overdue one. Spending two weeks fighting over a $25 fee that was never disclosed is a loss whether you win it or not.
How much can you legally charge
There is no single national cap on late fees for service-business invoices. There is, instead, a layered set of rules. Three layers matter for a service business sending invoices to homeowners or other businesses:
- Federal law for B2B work. No general cap on late fees for commercial invoices. The federal Prompt Payment Act sets a statutory interest rate for federal government contractors, set semiannually by the U.S. Treasury,2 but that applies only when the buyer is the federal government, not to general business-to-business work.
- State law. Most states do not impose a hard cap on late fees for commercial invoices. Virtually all of them require the fee to be "reasonable," which in practice means it has to look like a real estimate of damages, not a penalty. Some states cap the fee on consumer transactions at a percentage tied to a statutory interest rate. Published guides show maximums running from "no specific cap" in more than half of states to as low as 5 percent of the balance per month in a few.3
- The reasonableness rule. California Civil Code §1671 is the most cited illustration. A liquidated-damages provision, which is what a late fee is, is enforceable only if it represents a reasonable attempt to estimate the harm caused by late payment.4 Most state courts apply some version of the same test. A 1 to 1.5 percent monthly charge passes that test almost everywhere. A 10 percent monthly charge does not.
The number most service businesses settle on, including ones with accountants and lawyers behind them, is 1 to 1.5 percent per month of the unpaid balance, with a flat minimum of $25 to $50. That is roughly 12 to 18 percent annualized, well under the usury caps in every state, and high enough to motivate payment without crossing into territory that gets struck down. A flat minimum is the easier choice on small residential jobs; a percentage is the proportional choice on larger commercial work.3
A quick sanity check on the math. If your invoice is $640 and your terms say 1.5 percent monthly, the first month's late fee is $9.60. That is not a deterrent on its own. The deterrent is the second month's fee and the third, and the fact that the customer now has it on their books as growing. If the math feels too small, raise the flat minimum, not the percentage. Pushing the percentage past 1.5 percent monthly is where reasonableness arguments start.
Worked example: $480 handyman invoice
An illustrative case, since the math is the part that surprises most operators. Same invoice, same customer, two terms.
Terms on the invoice: "Net 15. A finance charge of 1.5% per month, with a $25 minimum, will be applied to balances unpaid after the due date."
| Day | What happens | Fee added | New balance |
|---|---|---|---|
| Day 0 | Invoice sent for $480.00 | n/a | $480.00 |
| Day 15 | Due date. Nothing paid. | n/a | $480.00 |
| Day 45 | One month past due. 1.5% of $480 = $7.20, below the $25 minimum, so the minimum applies. | $25.00 | $505.00 |
| Day 75 | Two months past due. Another $25 minimum charge. | $25.00 | $530.00 |
| Day 105 | Three months past due. Stop here and call (see below). | $25.00 | $555.00 |
Same wording on a $4,800 commercial invoice would behave differently. The first month's 1.5 percent fee is $72, which already exceeds the $25 minimum, so the percentage takes over for the first month and every month after. After three months unpaid, the balance is about $5,019. The point of the worked example is that the structure works for both sizes of job without you having to think about it on the day the fee triggers.
When the fee should kick in
Even with the fee disclosed up front, the question of when to start charging is a judgment call. The short answer is: not on the day after the due date. Build a small cushion in. The longer answer:
The grace period belongs in the wording, not in your head. Decide it ahead of time. Five days after the due date is a typical cushion in commercial agreements. Some jurisdictions write a 5-day grace period into law for related contexts, and a customer who has read theirs will expect one.3 State the grace period in the terms line on the invoice. Then the customer knows exactly which day the fee begins, and so do you.
The pre-due reminder beats the fee every time. The single most effective tool against late payment is not the late fee. It is the message you send two days before the due date. That is also the highest-converting reminder in the cadence covered in our guide to invoice reminders. Most invoices that go late do so out of forgetting, not refusing. Reminders catch forgetting; fees catch refusing, and refusing is rarer than it feels.
The first late fee is the firmest reminder you have left. Once the grace period closes, the fee is added on the next reminder, in writing, with the new total stated. "Invoice 1042 was due on June 1. Per the terms on the original invoice, a $25 finance charge has been applied. The new balance is $505." No apology. No "just." The wording is direct because the terms were disclosed weeks ago.
Stop adding fees after about three months and switch to the phone. Past around ninety days, fees are no longer a payment strategy. They are bookkeeping that makes the eventual write-off larger. At that point a phone call, or in some markets a small-claims filing, does more for collection than another finance charge. The cleaning invoice follow-up guide walks the full escalation path past day 30 in more detail, and the cadence translates to other trades with no real change.
The wording that makes the fee stick
The fee language on the invoice is short, specific, and dollars-not-feelings. Three working patterns. Pick one and use it everywhere.
Pattern 1: percentage with a floor
"Payment is due 30 days from invoice date. Balances unpaid after the due date are subject to a 1.5% per month finance charge, or $25, whichever is greater."
Best for most residential trades. The percentage scales with the size of the invoice; the floor keeps small jobs from generating fees too small to bother with.
Pattern 2: flat fee with grace period
"Payment is due 15 days from invoice date. Invoices paid more than 5 days after the due date are subject to a $35 late fee."
Best for one-and-done residential work where everything is under a thousand dollars. Simpler to enforce because there is no math to redo each month, and customers find a flat fee easier to accept than a percentage that compounds.
Pattern 3: percentage with annualized rate disclosed
"Net 30. Invoices unpaid after 35 days are subject to a 1.5% per month finance charge on the outstanding balance. Annualized rate: 18%."
Best for commercial work where the customer has an accounts-payable team. Disclosing the annualized rate looks like the credit-card line they already process, which makes it easier for AP to push through and harder to argue down.
A few things make all three of these patterns land:
- They state the actual number, not "subject to a late fee." Vague terms invite negotiation; specific terms invite payment.
- They name the grace period explicitly when there is one. "5 days after the due date" is unambiguous. "Promptly" is not.
- They show the annualized rate when the figure is high enough that the customer might ask. Eighteen percent reads like a credit card. A customer who recognizes that does not argue.
- They sit on the invoice itself, near the total. A late fee buried on page three of a contract gets fought. A late fee under the total gets paid.
When to drop the fee and call instead
A late fee is a tool for inattention, not for hardship and not for hostility. There are two situations where the right call is to set the fee aside and pick up the phone.
The first is when the customer has clearly run into trouble. A long-running residential customer who has paid every invoice for three years and is now sixty days late on a $2,200 deck repair is not refusing. Something is wrong, and the fee that lands in the next reminder will make the situation harder, not the work easier. A real call ("I noticed the invoice is still open, is everything OK on your end?") almost always either schedules a payment or produces an explanation you can work with. The fee can be reinstated on the next invoice if the conversation goes badly.
The second is when the customer has a real dispute. They believe a line item is wrong, the work was unfinished, or the price changed from what was quoted. Adding a finance charge to a disputed invoice is the surest way to convert a question into a refusal. Resolve the dispute first, in writing, and let the fee apply only to the corrected, undisputed balance from whatever new due date you agreed on.
The fee is most useful at exactly one part of the curve: the customer who can pay and is not paying because nothing has made it inconvenient enough to do so. For that customer, the fee on the next reminder is the inconvenience. The pricing guide for any service trade, like the handyman pricing guide or the cleaning pricing guide, assumes the fee is in the invoice template before it goes out. The only variable that changes from trade to trade is what you write on the next reminder, and which day you send it.
Put the fee in the template, not in the chase email
EosLog puts the late-fee terms on every invoice automatically, runs the reminder cadence for you, and adds the finance charge on schedule when an invoice goes past its grace period. You see what is outstanding at a glance and only get pulled in when an invoice needs you.
No credit card required. You can compare plans first, or try the free invoice generator to see what a clean payment-terms line and late-fee clause look like before you wire them into your invoice template.
Sources and further reading
- Nolo, "When Can I Charge Late Fees or Finance Charges?" (general legal framework: fees must be disclosed in the agreement before the invoice becomes overdue).
- U.S. Treasury, Bureau of the Fiscal Service, Prompt Payment (statutory interest rate set semiannually for federal-government invoices under the Prompt Payment Act, 31 U.S.C. §3902).
- Business.com, "How to Charge Late Fees and Interest on Unpaid Invoices" (state-by-state summary of late-fee caps and typical service-business rates, 2026).
- California Legislative Information, Cal. Civ. Code §1671 (reasonableness standard for liquidated-damages provisions, including late fees in California contracts).
This guide reflects general U.S. service-business invoicing practice as of 2026 and is not legal advice. Late fee rules vary by state and by contract type; rules for consumer customers can differ from rules for business customers in the same state. Verify any fee structure with your accountant or attorney before adding it to your invoice template.