Overdue Invoice Toolkit
Late fee calculator

Invoice late fee calculator for interest and overdue balances.

Estimate overdue days, daily interest, a flat fee and the updated invoice total before you follow up with a client.

Start with the invoice

Change any field and the result updates instantly.

Invoice Late Fee Calculator

Ready to copy
Days overdue0
Late fee$0.00
Updated total$0.00

Tool navigation

Late Fee CalculatorOpen the late fee calculator page.
Reminder EmailOpen the reminder email page.
Final NoticeOpen the final notice page.
Net 30 DateOpen the net 30 date page.
Follow-up ScheduleOpen the follow-up schedule page.

FAQ

How is the late fee calculated?The estimate combines daily interest from your annual rate with any flat fee you enter.
What are grace days?Grace days are ignored before the tool starts counting the invoice as overdue.
Should I charge a late fee every time?Not always. For small balances or valuable relationships, a polite reminder may be better than a fee notice.

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Invoice late fee calculator guide

Calculate the overdue balance before you decide what to send.

A useful late-fee calculation keeps the original invoice amount separate from any interest or charge you may be entitled to add. This tool is designed for estimating a clear next figure, not deciding whether a fee is legally enforceable.

How the calculator works

  1. Start with the due dateThe calculation counts days after the invoice due date, then removes any grace days you enter.
  2. Apply the annual rate as daily interestDaily interest is estimated from the invoice amount, annual rate and overdue days.
  3. Add an agreed flat fee only when appropriateUse a flat fee only when it is supported by your contract, terms or the rules that apply to the invoice.
  4. Review the updated balance before sending itUse the result as a working total, then check it against the invoice terms and any prior communication.
Should I charge interest on every late invoice?

Not necessarily. A short reminder is often the right first step. Charge interest or a late fee only where your agreement and the relevant rules support it.

What is the difference between a late fee and interest?

Interest grows with time and is based on a rate. A late fee is usually a fixed amount. Some invoice terms allow one, both or neither.

Can I use this calculator for any country?

The maths is general, but enforceability is not. Check the contract terms and local requirements before presenting a late fee to a client.