Late Fee Calculator
Calculate the exact late fee or interest charge on an overdue invoice. Supports both simple and compound interest methods.
Calculate your late fee
Interest accrues only on the original principal for each day overdue.
Formula: Principal × Rate × Days ÷ 365
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How Late Fee Calculation Works
Three steps to estimate what you can charge on overdue invoices.
Enter invoice details
Input the original invoice amount, the annual interest rate you charge, and how many days the payment is overdue.
Choose interest type
Select simple interest for a straightforward calculation, or compound interest if your terms specify monthly compounding.
Get your results
See the late fee and total due instantly. Use these figures when following up with your client.
Frequently Asked Questions
Common questions about late fees and interest charges on invoices.
Next step
Send the next invoice before it is late
Late fees are the remedy. Clear terms and an invoice that can be paid online are the prevention. Make one now, download the PDF or save it into a new account.
Make an invoice now
Start with the details that belong on your invoice.
6 fields, about a minute
12 × $15.00$180.00
Current total
$180.00
No signup, no card. Everything happens in your browser.
Invoice preview
This is what your client sees.
Green Acre Landscaping
INVOICE
INV-202609-001
Issued
Sep 25, 2026
Due
Oct 25, 2026
Currency
USD
From
Green Acre Landscaping
Bill to
Riverside Cafe
| Description | Qty | Rate | Amount |
|---|---|---|---|
| Lawn maintenance, June | 12 | $15.00 | $180.00 |
Payment due within 30 days. Thank you for your business.
Live preview, updates as you type
Automate Late Fee Tracking
Stop calculating late fees manually. Invoice My Clients automatically tracks overdue invoices and calculates interest charges for you.
Related resources
Learn more about interest on invoices and overdue payment workflows.