Calculate overdue invoice interest based on principal, annual rate, and days late.
Last updated: February 23, 2026
Days past the payment due date (Net 30)
Late payments are one of the biggest cash flow challenges for freelancers and small businesses. Charging interest on overdue invoices compensates you for the time value of money and incentivizes clients to pay on time.
Daily Interest = Invoice Amount × (Annual Rate / 365)
Interest accrues from the day the payment becomes overdue (after the payment terms expire). For example, on a Net 30 invoice, interest begins on day 31. Many businesses also charge a flat late fee in addition to interest.
Late payment terms must be disclosed in your contract or on the invoice before the work begins. Many jurisdictions cap the interest rate you can charge (typically 1-1.5% per month or 12-18% annually). Check your local usury laws before setting rates.
Beyond charging interest, consider requiring deposits or milestone payments for large projects, offering early payment discounts (such as 2/10 Net 30), and using automated invoicing software that sends reminders before and after due dates.
Calculate overdue invoice interest based on principal, annual rate, and days late. This tool runs in-browser for fast results without account setup.
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