Invoice Late Fee Calculator

Type the unpaid invoice amount, how many days it is overdue and the late fee your terms allow, and this calculator shows the fee and the new total to request. It handles a flat fee, a percent per month charged per started month or by the day, and a yearly interest rate charged by the day.

What you enter

  • Unpaid invoice amount
  • Days past the due date
  • How the late fee is charged
  • Late fee rate
  • Flat late fee

What you get

  • Late fee
  • New balance due
  • Months charged

How it works

  1. Enter the amount still unpaid on the invoice.
  2. Enter how many days past the due date it is. The invoice due date calculator on this site can give you the due date.
  3. Choose how your terms charge late fees and type the rate or flat amount written in your contract or on the invoice.
  4. Read the late fee and the new balance, and add the fee as its own line on a reminder invoice.

Three ways late fees are written

A flat fee is the simplest: a fixed amount, such as $25, added once when the invoice becomes overdue. It is easy to explain and suits small invoices, where a percent would come to only a few cents.

A percent per month, often written as 1.5% per month, is common on business invoices. Some terms charge it for every month or part of a month that the balance is late, others charge it by the day. A yearly rate, typical in contracts, is almost always applied by the day. Read your own terms to know which you promised.

When the number misleads

The result assumes the whole amount has been unpaid for the whole period. If the client paid part of the invoice along the way, work out each period separately on the balance that was actually outstanding, then add the pieces.

A fee you can calculate is not always a fee worth sending. For a good client who is a few days late, waiving the fee once can be worth more than the money. Many businesses mention the fee in the first reminder and only add it if the second reminder is ignored.

Tips

  • Only charge a late fee your client agreed to in advance, written in your quote, contract or the original invoice terms.
  • A friendly reminder a day or two after the due date gets many invoices paid before a fee is needed. Use the fee as the backstop, not the first move.
  • Check the legal limit where you and your client are based. Some places cap late fee rates or require specific wording, and those rules change.
  • Show the fee as a separate line so the client can see the original amount and the charge clearly.
  • Keep a record of the date you sent each reminder. It helps if a dispute ever needs to be settled.

Frequently asked questions

How is a monthly late fee calculated?

Multiply the overdue amount by the monthly rate. With per started month, each month or part of a month adds a charge, so a $2,000 invoice 40 days late at 1.5% per month counts as 2 months: $2,000 x 1.5% x 2 = $60.

How do I charge late interest by the day?

Divide the yearly rate by 365, then multiply by the overdue amount and the number of days. A $1,000 invoice 30 days late at 12% a year is $1,000 x 0.12 / 365 x 30 = $9.86.

Is a monthly percent the same as a yearly rate divided by 12?

Close, but not identical when you charge by the day. This tool converts a monthly rate to a daily one as rate x 12 / 365, so 1.5% a month for 30 days gives slightly less than one full month.

Should the fee compound?

This calculator uses simple interest, charged on the unpaid amount only, not on earlier fees. That is the common and simplest approach for small business invoices.

Is this legal or accounting advice?

No. It is an estimate of the arithmetic only. Whether you can charge a late fee, and how much, depends on your contract and local law, so check with an accountant or lawyer if unsure.

Related: Invoice due date calculator, Invoice generator, Payment processing fee calculator.

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