Late fee calculator
Type what is still owed on the invoice and how many days it is past due, then choose a flat fee or a percentage a month. This works out the fee and the new total. It runs in your browser — nothing is sent anywhere and nothing is saved.
Check your state before you charge one
The calculator does arithmetic. Whether you can charge the result is a separate question, and the answer depends on where you work and who the customer is. Three things are common enough to check for:
- Many states limit late fees or interest on unpaid bills. The limit, and whether it applies, can differ for a homeowner and for a business customer.
- Many require the fee to be agreed in advance — written into the contract, the signed estimate or the payment terms before the work starts. A fee that first appears on an overdue invoice is the easiest kind to dispute.
- A monthly percentage may be treated as interest, which can bring a state’s interest-rate rules into play even where a modest flat fee would not.
This page does not give a maximum, because there is no national one and a number here would be wrong in some state. Ask your state attorney general’s consumer protection office, your licensing board if you hold a trade license, or a local attorney. This is general information, not legal advice.
How the fee is worked out
- Flat fee: charged once as soon as the invoice is late, whatever the number of days. $25 on a $1,200 invoice is $25 whether it is a day late or a month.
- Percentage, simple: amount × monthly rate × months late. Months are counted as days ÷ 30, so 45 days is 1.5 months. $1,200 at 1.5% a month for 45 days is $1,200 × 0.015 × 1.5 = $27.00.
- Percentage, compounded: each month’s fee is charged on the earlier fees as well: amount × ((1 + rate)months − 1). The same invoice comes to $27.10. Over a year the gap grows — on $1,000 at 1.5% a month it is $180 simple against $195.62 compounded.
Some agreements charge a full month for any part of one, so 31 days counts as two months. If yours does, enter the days as whole months (30, 60, 90) to match. A monthly rate also reads bigger than it looks: 1.5% a month is 18% a year before any compounding, which is why the calculator shows the yearly figure next to it — state limits are often written as a yearly rate.
Flat fee or percentage?
A flat fee is simple to explain and simple to check: one number, once. It is often the better fit for small jobs, where a percentage of a $300 invoice comes to a few dollars and is not worth the conversation. A monthly percentage grows the longer the bill sits unpaid, which gives a larger customer a reason not to let it drift — and it is also the kind of fee most likely to be treated as interest.
Some businesses combine the two, or offer a grace period of a few days before anything is added. Whichever you choose, the version that holds up is the one the customer saw and agreed to before you started.
Putting it on the paperwork
Terms that customers can see usually read something like: “Payment due within 15 days of the invoice date. Balances unpaid after the due date will be charged [your fee], where permitted by law.” Put them in the contract or the signed estimate as well as on the invoice, so the fee was agreed before the bill went out.
When you do charge it, add it as its own line — “Late fee on invoice 1043, 45 days” — on a new invoice or statement that refers to the original, rather than changing the invoice the customer already has. On this site that is a new invoice with the fee as a line item; the papers here do not yet have a free-text terms box, so if you charge late fees, set the terms out in your written agreement or in the message you send with the estimate.
Charging a fee is not the same as getting paid
A late fee is a nudge, not a collection method. Plenty of businesses waive it when the customer pays the original amount promptly after a reminder, and keep the goodwill. The guide to what to do about a past-due invoice has the reminder timeline and three emails to copy — friendly, firm and final — and what your options are after that. To find the date the clock starts from, the Net 30 calculator turns an invoice date and terms into a due date, and what makes an invoice collectable covers the rest of what an unpaid bill needs behind it.
Questions about late fees
What is a typical late fee on an invoice?
There is no standard one. On small-business invoices you will often see a monthly rate of around 1% to 1.5%, or a one-off flat fee in the tens of dollars. Seeing a figure often is not the same as it being allowed where you work: states set their own limits, sometimes different ones for homeowners and for businesses, so check yours before you put a number in your terms.
Can I charge a late fee that was not in my contract or on the invoice?
It is much harder. In many states a late fee or interest is only collectable if the customer agreed to it before the work — in a contract, a signed estimate or the payment terms. A fee that first appears on an overdue invoice is easy for a customer to dispute. If you have no agreed terms, the practical move is to add them for future jobs and ask your state what applies to this one.
Is a late fee the same as charging interest?
Not always. A flat fee is a fixed charge for paying late; a monthly percentage behaves like interest, and some states treat it as interest, which can bring their limits on interest rates into play. How your state classifies each one decides which rules apply, so it is worth asking about the kind of fee you actually plan to use.
When does the late fee start?
Whenever your terms say it does. Commonly it is the day after the due date, and some businesses allow a grace period of a few days first. Write the start into the terms so there is nothing to argue about; the Net 30 calculator gives you the due date to count from.