Invoice Late Fee Calculator
Enter the invoice amount, days overdue, and interest rate to see how much late payment interest is owed.
Simple interest: invoice amount x rate x (days / 365).
late fee after 30 days at 8% per year
This tool calculates the late payment interest on an overdue invoice using simple annual interest, with preset rates for common jurisdictions.
Late payment is a major issue for freelancers and small businesses. In the UK, the Late Payment of Commercial Debts Act entitles businesses to charge 8% above the Bank of England base rate on overdue invoices. In practice most businesses do not charge it, but knowing the figure gives you a useful data point when chasing payment.
How we work it out
We use simple interest: invoice amount multiplied by the annual rate divided by 100, multiplied by days overdue divided by 365. This matches the standard calculation used by most late payment legislation and business contracts.
Questions
What is the UK statutory rate?
The Late Payment of Commercial Debts Act 1998 sets the statutory rate at 8% above the Bank of England base rate for business-to-business transactions. The base rate changes periodically, so the effective rate does too. 8% is used here as a baseline, not a live rate.
Do I have to charge late fees?
No. Statutory late payment interest is a right you can exercise, not an obligation. Many businesses choose not to charge it to preserve the client relationship. That is your call.
Is this compound or simple interest?
Simple interest only. Compound interest would increase the figure further, but most late payment legislation and standard contract terms use simple interest.
Waiting on payment. At least the interest is ticking.