How do I calculate a late fee on a repair invoice?

Take the monthly rate your written terms state, divide it by 30 for a daily rate, and multiply by the unpaid balance and by the number of days past the due date after any grace period. Add any one off administrative fee your terms allow. The calculator on this page does that arithmetic as you type.

What late fee can a mechanic legally charge?

That depends on your state and on what your written terms say, and this page deliberately does not answer it. Limits on late fees and finance charges are set by state law, they differ, and a page that printed a maximum would be wrong for most of the people reading it. Check your own state rules, and take advice if the amount matters.

Can I add a late fee if my invoice never mentioned one?

Adding a charge the customer never agreed to is a good way to turn a slow payment into a dispute. The usual fix is forwards rather than backwards: put the terms on the estimate, get them approved with the work, and the fee is agreed before it is ever needed.

Is a late fee the same as interest?

Not always, and the distinction can matter legally. A flat administrative charge and a percentage that accrues over time are different things, and some rules treat them differently. The calculator keeps them as separate fields for that reason rather than rolling them into one number.

Calculator

Mechanic invoice late fee calculator

Apply the late payment rate already written into your own invoice terms to an unpaid balance and the days it is overdue. Late fee limits vary by state, this page states no maximum, and none of it is legal advice.

Unpaid balance

What is still owed on the invoice, not what the invoice was originally for.

Monthly rate in your written terms

Copy the figure off your own invoice terms. If your terms say nothing, there is nothing to charge.

Days past the due date

Counted from the due date on the invoice, not from the day the work was done.

Grace days before anything is charged

Days after the due date you let pass for free. Zero if your terms give none.

One off administrative fee

Only if your written terms state one. Leave it at zero otherwise.

Late charge on those terms

$12.60

New balance $852.60. Whether a rate this size is enforceable where you work is a question for your state, not for this page.

Chargeable days after grace: 30
Daily rate, monthly divided by 30: 0.05%
Interest on the balance: $12.60
Administrative fee: $0.00
Same monthly rate stated yearly: 18.0%

Read this before the calculator

Late fees on an unpaid invoice are regulated, and the rules are not the same in every state. Some cap what may be charged on a consumer debt, some require the charge to be disclosed in a particular way before the work starts, and some treat a fee that is really a penalty differently from one that is really interest. This page does not tell you what you may charge, does not state a maximum, and does not say that any rate is lawful where you work.

It does one job: it takes a rate you have already agreed with your customer in writing and works out what it comes to on a given balance after a given number of days. If your invoice terms do not mention a late fee at all, there is usually nothing to apply, and the answer to that problem is a change to your terms rather than a charge added after the fact.

This is arithmetic, not legal advice. Check your own state rules, and if a balance matters enough to fight over, check them with somebody qualified.

The formula, written out

A rate written by the month has to become a daily one before it can be applied to a part month. This calculator divides the monthly percentage by 30 to get a daily percentage, multiplies that by the balance still unpaid, and multiplies again by the number of chargeable days. Chargeable days are the days past the due date minus whatever grace period your terms give.

Any one off administrative fee your terms allow is then added on top, once, rather than per day. The total is the late charge, and the balance the customer owes is the original balance plus that charge.

The divisor is a convention, not a law of nature. Dividing by 30 is the simplest way to do it and is what this page uses. Terms written as an annual rate applied over 365 days, or applied on calendar month boundaries, land on a slightly different figure. If yours are written either of those ways, use the divisor your own terms imply rather than this one.

The daily rate is the number that surprises people

A monthly percentage sounds small and a daily one sounds smaller still. In the example this page opens with, 1.5% a month is 0.05% a day, which on the unpaid balance is well under a dollar a day. That is why a fee like this rarely frightens anybody into paying.

Stated as a yearly rate the same figure is 18.0%, which sounds like a completely different animal and is the same number. Both are worth knowing before you set your terms: the daily figure is what the customer feels, and the yearly figure is what a regulator, or an annoyed customer with a search engine, will compare it against.

The practical conclusion is that a late fee is a signal rather than a revenue line. What actually gets a repair invoice paid is asking for the money on the day the work is finished, while you are still standing next to the car, rather than sending something a week later and waiting.

What makes a late fee stick

Three things, none of them arithmetic.

It has to be in writing before the work starts, on the estimate the customer approved, not first mentioned on the overdue invoice. It has to be a number the customer saw and agreed to, which in practice means the terms have to be somewhere they actually read rather than in small print nobody opened. And it has to be applied consistently, because a fee waived for everybody who complains is a fee that has already been abandoned.

The grace period field exists for that last point. A written grace period is a much easier thing to enforce at the end of it than an unwritten habit of letting the first week slide.

The example the calculator opens with, done by hand

Unpaid balance: $840.00
Monthly rate from your own terms: 1.5%
Monthly rate divided by 30, the daily rate: 0.05%
Days past the due date: 30
Grace days given: 0
Chargeable days: 30
Balance times daily rate times days: $12.60
One off administrative fee: $0.00
Late charge, and a new balance of: $12.60 on $852.60

Questions people ask about late fees on repair invoices

How do I calculate a late fee on a repair invoice?: Take the monthly rate your written terms state, divide it by 30 for a daily rate, and multiply by the unpaid balance and by the number of days past the due date after any grace period. Add any one off administrative fee your terms allow. The calculator on this page does that arithmetic as you type.
What late fee can a mechanic legally charge?: That depends on your state and on what your written terms say, and this page deliberately does not answer it. Limits on late fees and finance charges are set by state law, they differ, and a page that printed a maximum would be wrong for most of the people reading it. Check your own state rules, and take advice if the amount matters.
Can I add a late fee if my invoice never mentioned one?: Adding a charge the customer never agreed to is a good way to turn a slow payment into a dispute. The usual fix is forwards rather than backwards: put the terms on the estimate, get them approved with the work, and the fee is agreed before it is ever needed.
Is a late fee the same as interest?: Not always, and the distinction can matter legally. A flat administrative charge and a percentage that accrues over time are different things, and some rules treat them differently. The calculator keeps them as separate fields for that reason rather than rolling them into one number.