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.
What you can do here
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.
Preparing your calculator with today’s date…
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.
Use the result when creating your invoice in InvoiceAgent. Planner setup links carry the settings they describe into a draft. Review your dates, amounts, PDF, and reminder settings before scheduling.
Move from the quick answer into the rest of the invoice system.
Late payment calculator guide
Late payment calculator guide
Use the editorial calculator page for overdue-fee context, follow-up strategy, and related resources.
Payment reminders
Payment reminders
Use overdue calculations alongside reminder templates and escalation workflows that stay professional.
Invoice templates
Invoice templates
Use the result inside invoice formats that are ready for clients and easier to automate.
Knowledge base
Knowledge base
Review the billing concepts behind the numbers before they go onto a live invoice.
Profession pages
Profession pages
See how freelancers, consultants, and agencies apply the same calculator output in different workflows.