Earnvella
English

Invoice Late Fee Calculator

Work out the late fee on an overdue invoice using a monthly percentage, an annual rate or a flat charge, with an optional grace period.

Last reviewed 2026-11-09

Your numbers

$
d
d
%
$

Results

Days charged
30
Late fee
$37.50
Total now due
$2,538
Equivalent annual rate
18%

Results update as you type.

Estimates for planning only. This is not tax, legal or financial advice. Read the full disclaimer.

Common late fee structures

A flat fee is simple and easy to explain. A percentage per month, such as 1.5%, is common in service agreements and works out to 18% a year when simple interest is applied. An annual rate, expressed as a percentage per year, is prorated by the number of days late.

This calculator prorates monthly rates over a 30-day month and annual rates over 365 days, using simple interest and no compounding. You can also add a flat fee on top of a percentage. Grace days are subtracted before any percentage is applied.

Make the fee enforceable

A late fee is far easier to collect when it is stated in your contract or on the invoice before the work begins, together with the payment due date. Some jurisdictions limit how much interest or penalty you can charge, and rules can differ for consumers and businesses. Check local rules or ask a professional before setting your rate.

Many freelancers use late fees mostly as a deterrent and waive them for first-time delays. Friendly reminders at one day and one week overdue also help.

Write late payment terms before the project starts

A late fee is only enforceable if the client agreed to it in advance. A simple clause is enough: "Invoices are due within 30 days. Overdue balances accrue 1.5% interest per month." Put the same wording on every invoice.

Rules differ by state and country, and some places cap late fees or interest. Check the limits that apply to you before you set a rate.

Frequently asked questions

How do I calculate a 1.5% monthly late fee?

Multiply the invoice amount by 1.5% for each month late. This tool prorates by days over a 30-day month, so 45 days late is 1.5 months, or 2.25% of the invoice.

Is a flat late fee better than a percentage?

A flat fee is predictable. A percentage scales with the invoice size and grows with delay, which encourages faster payment on large invoices.

Can I charge late fees without a contract?

It is much harder. State the terms in a contract or on your invoice in advance, and check local rules.

Does this calculator compound interest?

No. It uses simple interest, which is how most late fee clauses are written.

What is a reasonable late fee for an invoice?

Many freelancers use 1% to 1.5% per month on the overdue balance, or a flat fee. Legal limits vary, so check your local rules.

Can I charge a late fee that is not in the contract?

Generally not. Late fees should be agreed in writing before the work starts.

How do I get a client to pay an overdue invoice?

Send a polite reminder, then a firmer message that references the due date and the agreed late fee. Offer a payment plan before escalating.