Free Late Payment Calculator
Use this calculator to estimate what an overdue invoice might look like after a flat late fee and time-based late interest are applied.
Why this page exists
Estimate flat fees, overdue interest, and the updated amount due on a late invoice.
Built for real invoice workflows
Once the amount is clear, InvoiceAgent can help automate the reminder sequence around it.
Original invoice
$2,400.00
Flat fee
$45.00
Interest
$14.20
Updated total
$2,459.20
How to use it
Enter the original invoice total.
Add any flat late fee and annual late rate you want to test.
Set the number of days overdue to see the updated total.
Why it helps
Helps you quantify overdue invoice scenarios before sending a stronger reminder.
Useful when comparing a simple flat fee against a fee plus interest.
Makes late-payment follow-up easier to explain in a final reminder.
From free tool to live invoice workflow.
Once your numbers and dates look right, InvoiceAgent can create the scheduled invoice, generate the PDF, send reminder emails, and dispatch it with live FX conversion at send time.