Free Late Fee Calculator
Enter your invoice amount, days overdue, and state to calculate the maximum legal late fee. Includes your state's interest rate cap and total amount now due. Free, no signup required.
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Frequently asked questions
How is the late fee calculated?▾
The calculator multiplies your invoice amount by the applicable monthly interest rate and the number of months overdue (days / 30). If you enter an agreed rate, it uses that — capped at your state's legal maximum. If you leave the rate blank, the state maximum is applied.
Is the state maximum rate always what I can charge?▾
Not necessarily. The state maximum is the legal ceiling. You can only charge what's specified in your contract or invoice terms. If your contract says 1% per month but the state allows 1.5%, you can only charge 1%. If you have no agreed terms, courts may apply the state's default judgment rate.
Can I add late fees if my contract doesn't mention them?▾
It depends on your state. Some states allow statutory interest on overdue amounts even without a contract clause. However, having late fee language in your invoice or contract makes enforcement much easier. Our Payment Terms Generator can help you draft this language.
Does this calculator account for compound interest?▾
No. This calculator uses simple interest (the most common method for invoice late fees). Most states limit late fees to simple interest. If your contract specifies compound interest, consult an attorney to confirm it's enforceable in your state.
What should I do after calculating the late fee?▾
Send a formal reminder or demand letter to your client with the updated total. Our free Demand Letter Generator can help you create a state-aware letter. Or let InvoiceFlows automate the entire reminder process — $9/month with a 30-day free trial.
Learn more
How to add late fees to an invoice