Late Payment Interest Calculator
Find out exactly how many days an invoice is overdue and how much interest is owed, then copy a ready-made reminder message — all calculated instantly in your browser.
To calculate late payment interest, enter the invoice amount, due date and your annual interest rate — days overdue, interest owed and total now due are calculated instantly, along with a copyable reminder message.
Enter the invoice amount and due date to see interest owed.
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How to use Late Payment Interest Calculator
- 1Enter the invoice amount and due date.
- 2Enter the annual interest rate from your contract or local statutory rate.
- 3See days overdue, interest owed and the new total instantly.
- 4Copy the ready-made payment reminder message.
Why invoices go unpaid — and what to do about it
Roughly 4 in 10 small-business invoices are paid late, straining cash flow. Charging late interest — and clearly communicating it — is a standard, professional way to encourage on-time payment.
This calculator uses simple daily interest: annualRate ÷ 365 × daysOverdue × invoiceAmount, the same convention used by most invoicing software and late-payment statutes.
Setting your interest rate
Many contracts specify a late-fee rate; if yours doesn't, check your local statutory late-payment interest rate (these vary by country and change periodically) or use a conservative default like 1.5%/month (18%/year).
Frequently Asked Questions
How is the interest calculated?
Simple daily interest: (annual rate ÷ 365) × days overdue × invoice amount. This is the standard convention used by most invoicing tools and late-payment regulations.
Can I use this for statutory late payment interest?
Yes, as long as you enter the correct statutory annual rate for your jurisdiction — this tool doesn't look up rates automatically, since they vary by country and change over time.
Is my financial data uploaded anywhere?
No. Every calculator on this site runs entirely in your browser — nothing you enter is sent to a server.
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