Working out what a late invoice should cost the client? Enter the invoice amount, how many days it is overdue and the interest rate or fee you agreed, and this free calculator shows the late charge and the new total due.
| Interest charged | – |
| Interest per extra day | – |
How it works
This calculator uses simple interest. Interest = invoice amount × yearly rate × days overdue ÷ 365. Any flat fee is added on top. Total due = invoice amount + interest + flat fee.
The tool does not know what you are allowed to charge. Late fees and interest can be limited by law and by what you agreed in writing, so check the rules where you and your client are based.
Worked example
A 1,000 invoice is 30 days overdue at 8% a year. Interest is 1,000 × 0.08 × 30 ÷ 365 = 6.58. With no flat fee the total due is 1,006.58.
Tips
- Put your late fee terms in your contract and on every invoice before you need them.
- A polite reminder often works before you add a charge. See our unpaid invoice email templates.
- Some freelancers waive the fee for a first late payment to keep the relationship good.
Frequently asked questions
Can I charge a late fee on any invoice?
Only if it is allowed where you work and was agreed in advance, for example in your contract or on your invoice.
Is interest calculated daily?
This tool uses a simple daily calculation from a yearly rate. Some agreements use monthly or compound interest.
What rate should I use?
Use the rate in your contract or the rate that applies by law in your country. We do not provide legal rates.
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This calculator is general guidance, not legal advice. Late fee rules differ by country.