Late fees that hold up

The invoice is 52 days old. On the second reminder you added a line — "1.5% late fee, $42" — and the customer wrote back in one sentence: "I never agreed to that." They are probably right. The estimate they signed said nothing about a late fee, and neither did the first invoice. You can keep asking for the $2,800. The $42 is gone.

The practical point is simple: there is no single nationwide late-interest rate for a private contractor invoice. A late fee is normally a term of your agreement. If it was not in the agreement before the work, do not assume you can add it later.

General business guidance, not legal advice. Late charges on consumer invoices are governed by state law — usury limits, consumer-protection rules, and in some states contractor-specific rules. Check your state attorney general's consumer protection division and have a local attorney read your clause once.

It has to be in writing before the work starts

Three documents carry the term, and the order matters:

1. The estimate or contract the customer approves. This is the one that counts. A fee the customer agreed to in writing before you bought material is a term of the deal.
2. The invoice. Restate it here, with the due date and the date the fee would begin. A term nobody can find on the bill is a term you will end up arguing about.
3. The reminder. Reference the clause, do not introduce it.

A fee that first appears at step 2 or step 3 is a request. On commercial and public work, a prompt-payment statute may create a separate rule, but its scope varies enough that it is worth asking a construction attorney rather than assuming your job qualifies.

Flat fee, monthly percentage, or both

Three structures cover almost everything contractors use. On a $2,800 invoice, the amount changes sharply with the method you write:

Choose a structure only after checking what your state permits.

Note the gap between rows two and three. Same stated rate, different result, because "per month" is ambiguous and nobody writes down which they meant.

Flat fees suit small tickets: on a $340 drain cleaning, 1.5% is $5.10, which is not worth printing. Percentages suit larger jobs, where a flat $40 on a $14,000 balance is a rounding error. Plenty of trades use a flat fee under a threshold and a percentage above it.

The fee is a deadline, not income

Run the arithmetic before you decide how hard to push. At 1.5% per month on a $2,800 balance, simple, no compounding:

Ninety days of chasing earns $126. That does not pay you for the phone calls. The fee's value is that it puts a cost on the date, which changes behavior in an accounts-payable queue where your invoice competes with others. Treat the revenue as incidental and you will make better decisions about when to charge it.

What the clause has to nail down

Write the operating details, not just the rate.

• When it begins. A grace period of 5 to 10 days after the due date is common and reads as reasonable. Write the mechanism: "10 days after the invoice due date," not "if payment is late."
• What it applies to. The unpaid balance, and whether partial payments reduce it. If a customer pays half, the fee should run on the half that is outstanding.
• Monthly or daily. Per month started, or prorated per day. Pick one, and give the daily divisor if you prorate.
• Whether it compounds. Most contractor clauses do not, and simple is easier to defend. Say so.
• The rate in annual terms too. "1.5% per month (18% per year)." Some states require an annual figure on a periodic rate, and stating it also protects you from a customer claiming they read 1.5% as annual.
• A cap or a stop date, if you want one. Some contractors stop accrual at 90 days and move to collections instead of letting a charge grow past what a judge would look at kindly.

One more, and it is not part of the clause: charge it consistently. If you have never once applied the fee and then apply it to a single customer, it looks like retaliation rather than policy — and in small claims the question you get asked is where the term is written and whether you enforce it.

Where state law puts the ceiling

This is the part to check locally rather than copy.

Usury caps are state law, they differ between consumer and commercial transactions, and they are not all in the same neighborhood. An 18% annual equivalent is above what some states allow on consumer accounts, and some states also cap late charges on specific kinds of contracts separately from the general usury statute. A rate over the limit is not just unenforceable in some states — it can carry a penalty of its own.

The words matter as well. "Finance charge" has a defined meaning in federal consumer credit law, and whether a term that lets a customer pay later brings any disclosure obligation with it depends on facts specific to your business. Most one-off contractor invoices do not, but if you routinely let customers pay over time, that is a conversation for an attorney and not a template.

Start with your state attorney general's consumer-protection pages and contractor licensing board, which may have residential-contract requirements. Then have a local attorney review the clause you plan to reuse.

Getting the term onto the document the customer signs

The clause only works from the document the customer approved, which means it has to be there every time and not just when you remember. Keep your terms with your estimates in DoneQuote and the late-fee language goes out with the priced work, so the version the customer agreed to is the version you can point at 52 days later. The fee you wrote is the fee on the record.

If the work is already done and there is no clause

You cannot add one retroactively, and trying tends to cost you the goodwill you still need to get paid at all. What you have instead is the reminder sequence, a call, a payment plan if the money is genuinely not there, and — on larger jobs — mechanic's lien rights that run on their own statutory deadlines and matter far more than $126 ever will.

Then fix the paperwork for the next job. Write the clause this week, while the argument is still annoying you enough to do it.