Days past due is the number of calendar days between an invoice’s due date and the date you are checking it. An invoice due on September 1 is 1 day past due on September 2. Enter the due date and a comparison date to see how late an invoice is. No amount, rate or customer details are needed.
days past due = as-of date − due date
The result counts calendar days and is never below zero. On the due date an invoice is 0 days past due; the following calendar day it is 1 day past due. Weekends, holidays and bank holidays are counted as ordinary days, and the tool does not interpret business-day payment rules.
This number is context. It does not decide whether interest or fees can be charged, and it does not decide which reminder stage to use — that depends on your agreement, earlier contact and local rules. The tool never changes your original invoice.
Count the calendar days from the due date to the date you are checking. An invoice due on September 1 is 17 days past due on September 18.
No. On the due date an invoice is 0 days past due. It becomes 1 day past due the following calendar day.
Subtract the due date from the as-of date, and use zero if the result would be negative.
Yes. This calculator counts every calendar day and does not apply business-day, weekend or bank-holiday payment rules.
No. Use the late payment interest calculator for a simple-interest estimate using a rate you enter. It does not determine any legal or statutory entitlement.
No. Which reminder stage to use depends on your own process, earlier contact and agreement. You choose the stage in the payment reminder generator.
No. The calculation runs in your browser and does not modify an invoice or send a message.
Reviewed 2026-09-29. This is a deterministic date calculation; it does not require an external tax or legal source.
