You can often charge interest or a late fee on an overdue invoice, but only if you set it up the right way. It usually has to be in writing before the job starts. The rate has to be legal in your state. And the customer has to be able to see it on the quote and the invoice. There is no single national rate for ordinary customer invoices, so the number you pick matters less than the paper trail behind it.
This guide is for solo plumbers, electricians, HVAC techs, handymen, landscapers, and cleaners. It covers what to write, how to do the math, what to skip, and how to avoid needing a late charge at all.
TL;DR
- There is no one US rate for late payment interest on customer invoices. Your agreement and your state's rules decide what is allowed.
- Put the due date and late terms on the quote, repeat them on the invoice, and get the customer to approve before work starts.
- Simple interest is easy: balance × yearly rate × days late ÷ 365. A $1,200 invoice at 12% for 30 days is $11.84. That is an example, not a recommended rate.
- The IRS interest rate is for unpaid taxes. Do not copy it onto a customer invoice.
- Fast invoices, an online pay link, and steady reminders collect more money than a scary late fee does.
Table of Contents
- What "late payment interest" means for a trade business
- Who you are billing changes the answer
- The IRS rate is not your rate
- Step 1: Decide if you want a late charge at all
- Step 2: Pick terms that are simple and fair
- Step 3: Show how to calculate it
- Step 4: Get it in writing before the job
- Quote, estimate, invoice, deposit: keep them straight
- Step 5: Send the invoice fast and make paying easy
- When a bill is already overdue
- Our view: the best late fee is the one you never need
- Where Quotewren fits
- FAQ
- Sources
What "late payment interest" means for a trade business
When a customer pays you late, two things can be added to the bill. People mix them up, so let's separate them.
- Interest grows with time. It is a percentage of what is owed, charged for each day or month the bill stays open.
- A late fee is a set charge, like $25, or a one-time percentage, like 5%, added once the due date passes.
Both are "late payment charges." Which one you use, and what is allowed, depends on your state and your agreement. The Better Business Bureau tells businesses to look up their state's rules on maximum interest or fees before choosing a number. It also describes monthly fees of roughly 1% to 2% as common practice. Common does not mean legal everywhere. A rate that works in one state, for one type of customer, might not work in another.
We are not lawyers, and this is not legal advice. Before you print a rate on your paperwork, check your state's rules or ask a local attorney or your state's consumer or business office. That one phone call is cheap next to a dispute.
Who you are billing changes the answer
A homeowner, a landlord, a property manager, and a general contractor are not the same customer. Rules can differ by customer type and by how your business is set up. Think about these cases:
- A homeowner who hired you for a water heater swap. Residential customers often get more protection. Do not assume you can add a charge just because the invoice is overdue. Check the signed agreement and your state's rules first.
- A landlord with six rental units. This is closer to a business-to-business sale. Written terms still matter most.
- A general contractor who subs you for rough-in wiring. Your subcontract may already set payment terms and late charges. Read it before you add your own.
If you are not sure which bucket a customer falls in, treat the charge as something you must be able to prove they agreed to.
The IRS rate is not your rate
Search results for this topic are full of IRS pages. That is because "late payment interest" also describes what the government charges on unpaid tax. It is a different thing.
The IRS sets underpayment interest each quarter. For 2026, the published rates are 7% for January to March, 6% for April to June, 7% for July to September, and 7% for October to December. The IRS compounds that interest daily until the balance is paid.
Separately, there is a failure-to-pay penalty. IRS Notice 433 says the usual rate is 0.5% of the unpaid tax for each month or part of a month. It is lower, at 0.25% a month, while you are in an approved installment agreement, and it can go up to 1% a month after a levy notice. That notice is older, so check your own IRS account and current notices for your balance.
Here is what this means for you:
- If you owe the IRS, these rules apply to you.
- If a customer owes you, these rules say nothing about what you may charge.
- Do not copy the IRS rate onto an invoice and call it legal.
Step 1: Decide if you want a late charge at all
A late charge has two jobs. It nudges people to pay on time, and it covers some of your cost when they do not. But it also can sour a relationship, and collecting a small fee can cost more time than it is worth.
Some owner-operators use the charge mostly as a signal. They rarely collect it, and they waive it for good customers who pay a few days late. That is fine if the terms are clear and you apply them evenly. BBB's guidance makes this point: a late fee should be a predictable business term, not a reaction to one difficult customer.
If you would never enforce it, do not print it. A threat you do not follow through on teaches customers to ignore your due dates.
Step 2: Pick terms that are simple and fair
Keep it plain. A customer should read it in ten seconds. Here are common setups, with a $600 electrical repair as the example.
| Setup | How it works | On a $600 bill |
|---|---|---|
| Flat fee | One set charge after the due date | $25 once, if allowed |
| One-time percentage | A percent of the balance, added once | 5% adds $30 |
| Monthly percentage | A percent each month or part of a month | 1.5% a month adds $9 for the first month |
| Simple yearly interest | Daily math from a yearly rate | 12% for 30 days adds $5.92 |
These are examples to show the math. They are not rates we recommend or that any state has approved. Your state may cap what you can charge, or may treat some of these differently.
Two habits keep you out of trouble. First, use the same wording every time. Second, write the method, not just the number, so the customer can check your math.
Step 3: Show how to calculate it
For a simple late charge, use this formula, unless your contract and state law call for another method:
Balance × yearly rate × days late ÷ 365
Worked example for a handyman who finished a $1,200 deck repair:
- Balance: $1,200
- Yearly rate in your agreement: 12%
- Days late: 30
- $1,200 × 0.12 × 30 ÷ 365 = $11.84
That is simple interest. It does not compound, so it is easy to explain. If the customer pays 45 days late instead, the same bill adds $17.75.
A monthly rate is even simpler. A 1.5% monthly charge on $1,200 is $18 for a month. Pick one method and use it every time.
Notice what the numbers say. Interest on a normal home-service invoice is small. On a $1,200 bill, a month of 12% interest is less than twelve dollars. The real cost of late payment is that you wait for your own money. That is why prevention beats penalties.
Step 4: Get it in writing before the job
A late charge is much easier to enforce if the customer saw it before they said yes. BBB recommends clear payment deadlines, written contract terms, and a short version of your policy on every invoice. Follow this order:
- On the quote. Add your payment terms, due date, and the late charge wording. If you take a deposit, say so here too.
- On the signed approval or service agreement. Have the customer accept the quote that contains the terms.
- On the invoice. Repeat the due date and late terms near the payment section.
A short version might read: "Payment is due within 14 days of the invoice date. Balances unpaid after the due date may be charged 1.5% per month, calculated on the unpaid balance." Check that wording against your state's rules before you use it. Your attorney can adjust it in minutes.
For more on picking terms, see our guides on invoice terms solo contractors use and practical invoice late fees. If you want to ask for payment at the end of the job, our payment on completion checklist helps.
What a clear invoice shows
For a $600 electrical repair, the invoice should show:
- What you did, in plain words (replaced two GFCI outlets, rewired a kitchen switch)
- The total and the balance due
- The due date
- A payment link or other ways to pay
- A short late charge line, if you use one
If it takes the customer a minute to find any of that, you will get questions instead of money.
Quote, estimate, invoice, deposit: keep them straight
These words get tossed around, and mixing them up causes disputes.
- Estimate: a rough guess of cost. It can change once you open the wall or see the equipment.
- Quote: a firm price for a defined job. This is the best place to attach your terms.
- Deposit: money paid up front, before or when work starts. It reduces the balance later.
- Invoice: the bill for work done. It says what is owed and when.
If you use a deposit, show it on the invoice as a credit. Interest should only apply to the balance that is actually unpaid. Charging a late fee on the full job price when half was already paid is a quick way to lose a customer and a dispute.
Step 5: Send the invoice fast and make paying easy
The cheapest fix for late payment is operational. BBB's guidance points to prompt invoices, clear deadlines, convenient payment options, and automated reminders. Reducing friction often works better than making the penalty bigger.
Try this routine after every job:
- Invoice the same day. An HVAC tune-up invoice sent from the driveway gets paid faster than one sent Friday.
- Put the due date in plain view. Say "Due May 12," not just "Net 14."
- Add a pay link. Customers pay when it takes one tap. Our guides on online invoice payments and ACH payments show the options.
- Remind on a schedule. A friendly nudge before the due date, one on the day, and a firmer one after works for most jobs. See the six touch reminder schedule and the reminder setup guide. You can copy payment reminder email subjects too.
- Ask why. If a customer is late, ask what happened. A short payment plan can protect your cash and the relationship.
BBB also lists early-payment discounts as an alternative. A 2% discount for paying within 7 days costs you $12 on a $600 job. That might be less than the hours you spend chasing it.
When a bill is already overdue
Stay calm and keep a record. Here is a simple order:
- Check the due date and the terms the customer approved.
- Send a friendly reminder with the pay link.
- Call if there is no reply in a few days.
- Send a firmer written notice that states the balance, the due date, and any late charge in your agreement.
- If the customer still does not pay, talk to a local attorney or your state's small claims court office about next steps.
We lay out the steps and wording in our overdue invoice process templates.
A word of care: do not threaten anything you cannot or will not do, and do not add a charge that is not in your signed terms. If the customer is a homeowner, be extra careful, and check your state's rules before you add anything.
Our view: the best late fee is the one you never need
We build for solo operators, so we hear the same story a lot. The job went well. The customer was happy. Then the invoice sat for three weeks, and nobody wanted to be the person who brought up a late fee.
Here is what we have learned from that.
Terms beat penalties. A due date on the quote and invoice does more than a threat on page two of a contract. Customers pay people who are clear.
Speed is a form of collection. The sooner the invoice lands, the sooner the clock starts, and the fresher the work is in the customer's mind.
Do not make it personal. A late charge should be a standard term that applies to everyone. When it is, you are not the bad guy. The paper is.
Cash flow and reviews go together. The same moment a customer is happy enough to pay is the moment they are most likely to leave a Google review. If you chase money and reviews as two separate chores, one of them gets dropped. We built Quotewren so quote, invoice, and review request live in one flow.
— jaras
Where Quotewren fits
Quotewren turns finished jobs into branded quotes, then invoices with pay links, then sends a three-touch review request by SMS after the job is done. It is made for solo operators, with flat pricing instead of features that big field service teams need. You can start on the Free plan. The paid plans are Quotewren at $19 per month and Quotewren Crew at $39 per month.
You can write your payment terms and due date into your quotes and invoices, then add a pay link so customers can pay right away. Try Quotewren on your next job. If you want a head start on the paperwork, our free quote templates and HVAC quote template are printable.
FAQ
Can I charge interest on a late invoice?
Often yes, but it depends on your written agreement and your state's rules. The customer should have seen the terms before work started. Check your state's limits or ask a local attorney before you print a rate.
How much interest is normal?
BBB describes monthly fees of around 1% to 2% as common practice. That is not a legal safe harbor, and some states or customer types may limit it. Look up your state's rules first.
Can I use the IRS interest rate on my invoices?
No. The IRS rate applies to unpaid federal tax. It does not set what you may charge a homeowner, landlord, or contractor. Your contract and state law decide that.
What is the difference between a late fee and interest?
A late fee is a set charge, like $25, or a one-time percentage added after the due date. Interest grows with time, by the day or month. Whichever you pick, state it plainly on the quote and the invoice.
What if I forgot to put late terms on the quote?
Do not add them after the fact and expect them to hold. Send a friendly reminder with the pay link, and ask about a payment plan if needed. Then add terms to every quote from now on.
Sources
- BBB Business Tip: How to set and enforce late payment penalties
- IRS quarterly interest rates
- IRS Notice 433