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Late Payment Interest Calculator

If an invoice is overdue, this works out exactly what you're owed: the original amount, interest, and any late fee. Then copy a firm but polite reminder to send.

Common references: many US contracts use 1.5% per month (18%/yr). UK statutory is 8% above the Bank of England base rate. The EU late-payment reference is 8% above the ECB rate. Use whichever rate your contract or local law allows.
Total now owed
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Days overdue—
Original amount—
Interest—
Late fee—

How late-payment interest works

Interest on an overdue invoice is usually simple interest: the outstanding amount, multiplied by the annual rate, multiplied by the fraction of a year it is late. This tool uses amount × rate% × days ÷ 365, then adds any flat fee your terms allow.

Can a freelancer charge interest?

Yes, in two situations: your contract or invoice states a late-payment interest rate, or your local law grants a statutory rate for overdue commercial invoices. If your written terms are silent and there's no statutory right, you can still ask, but you may not be able to enforce interest. That is a good reason to put a late-payment clause in every contract. You can copy one from the contract clause library.

The reminder ladder

  1. Day 1 overdue: a friendly nudge that assumes it just slipped their mind.
  2. Day 7: a firmer note restating the amount, due date, and how to pay.
  3. Day 14+: state the interest now accruing and a clear final date before further steps.

Keep it factual and unemotional. Most late invoices come down to disorganisation rather than malice, and a clear reminder with a payment link usually does the job. You can set stronger terms on your next invoice with the invoice generator.

Not legal advice. Rules on charging interest and fees vary by country and contract. Check what applies to you before enforcing a charge.

Frequently asked questions

What interest rate should I use?

Use the rate written in your contract or invoice. If you're relying on a statutory right, use the rate your country sets for late commercial payments. Don't invent a rate you never disclosed.

Does interest compound?

For overdue freelance invoices, simple interest (what this tool calculates) is the norm and the easiest to justify. Some jurisdictions allow compounding, so check the rules where you are.