Invoice Late Fee Calculator
Calculate the late fee on an overdue invoice: days late, monthly interest (simple or compound), flat fee and new total due. Free, private, no signup.
Not ready? Start with Freelancer Invoice Tracker ($9). See all templates.
How invoice late fees are calculated
Most freelancers and small businesses charge late payment as interest on the unpaid invoice, often 1% to 1.5% per month, and sometimes add a one-time flat fee. The calculator supports both and counts days from the invoice due date to the payment date (or today).
- Days late = payment date − due date − grace period (never below zero)
- Simple interest = invoice amount × monthly rate × days late × 12 ÷ 365. This spreads the monthly rate evenly over the days, so a partial month is charged fairly.
- Compound monthly = invoice amount × ((1 + monthly rate)days late × 12 ÷ 365 − 1). Interest is charged on earlier interest. Many places restrict compounding, so simple interest is the safer default.
- Total late fee = interest + flat fee (the flat fee only applies once the invoice is late after any grace period)
- Yearly rate = monthly rate × 12. 1.5% a month is 18% a year.
Worked example
A $2,000 invoice was due on September 15 and paid 45 days later, on October 30. Your terms say 1.5% per month with no grace period. Simple interest is $2,000 × 0.015 × 45 × 12 ÷ 365 = $44.38. If your contract also has a $25 late fee, the total is $69.38 and the client owes $2,069.38. With a 15-day grace period, only 30 days count and interest drops to $29.59.
Make the fee enforceable
- Agree on it up front. Put the late fee in your contract or proposal and repeat it on every invoice. A fee you didn't disclose in advance is hard to collect.
- Stay within the law. Many US states cap interest rates or late fees, and the rules differ for consumers and businesses. If you are unsure, use the wording "or the maximum rate permitted by law, whichever is less". This calculator is not legal advice.
- Sample wording: "Payment is due within 30 days of the invoice date. Late payments accrue interest of 1.5% per month (18% per year) on the unpaid balance, or the maximum rate permitted by law, whichever is less."
- Be consistent but human. Send a friendly reminder before the due date and on the day after. Many freelancers waive the first late fee for a good client in exchange for paying today. The fee still sets expectations.
Prevent late payments in the first place
Ask for a 25–50% deposit before starting, use shorter terms (Net 15 instead of Net 30) for new clients, invoice the same day you deliver and track every open invoice so nothing slips. Price the cost of slow payers into your rate with the freelance hourly rate calculator.
FAQ
What is a typical late fee for freelance invoices?
1% to 1.5% interest per month (12% to 18% a year) is common, sometimes with a flat $25–$50 fee. Check your state's limits and keep the fee reasonable relative to the invoice.
Can I charge a late fee if it wasn't in my contract?
It is hard to enforce a fee you didn't agree on in advance. You can still ask, but the stronger move is to add late-payment terms to every new contract and invoice.
Should I use simple or compound interest?
Simple interest is clearer and more widely allowed. Compounding increases the fee only slightly over a few months and can conflict with local rules.
Does the grace period remove the fee entirely?
If the client pays within the grace period, the fee is $0. After it ends, this calculator charges interest only for the days beyond the grace period. Some contracts instead charge from the original due date; match what your terms say.