Invoice Late Fee Calculator
Enter the invoice amount, an annual interest rate, and how many days it's overdue to calculate the late fee and the new total owed.
Put a real number on late payments
Late-paying clients are a tax on freelancers and small businesses, and a clearly stated late fee is the simplest deterrent. This calculator prorates an annual interest rate across the days an invoice is overdue, so you can show a client the exact fee they've accrued and the new total they owe — backed by a defensible formula rather than a guess.
The best late fee is the one you never have to charge, so state your terms up front: the rate, the grace period, and when interest begins. Because enforceable limits vary by jurisdiction, check your local rules before setting a rate. The per-day figure is useful in reminders — it makes the cost of continued delay concrete.
How it's calculated
Late fee = invoice × (annual rate ÷ 100) × (days overdue ÷ 365). Total owed = invoice + late fee. Per day = late fee ÷ days. Everything updates live in your browser.
Frequently Asked Questions
How is a late payment fee calculated?
A late fee is usually interest charged on the overdue amount. This tool prorates an annual interest rate over the days a payment is late: invoice × (annual rate ÷ 100) × (days ÷ 365).
What is a reasonable late fee to charge?
Common terms are 1–2% per month (roughly 12–24% annually), but the enforceable maximum varies by state and country. Check local law and state your terms on the invoice in advance.
Can I charge a flat late fee instead?
Yes. Many freelancers use a flat fee or a percentage, whichever is higher. This calculator focuses on the interest-based method; a flat fee is simply a fixed amount you add.
Is this calculator free and private?
Yes. It runs entirely in your browser with no sign-up, and nothing you enter is uploaded.
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