Finance calculator
Payment Due Date Calculator
Turn an invoice date and credit terms into a due date, and see how many days are left or overdue. Your entered values stay out of analytics.
Formula and assumptions
Due date = invoice date + credit days. Overdue days = as-of date − due date, when positive. Late fee = balance × rate ÷ 100 × overdue days ÷ 365.
- Credit days are counted as calendar days from the invoice date.
- A late fee is shown only if you enter both a balance and a rate. The rate is yours; none is assumed.
- The late fee is simple interest on the balance for the days overdue, using a 365-day year. It is an estimate for information, not a legal entitlement.
- The late fee is rounded to 2 decimal places (half up).
Formula version 1.0, last reviewed 1 October 2026.
Frequently asked questions
Are credit days calendar days?
Yes. Weekends and holidays are counted, so 30 days from 1 January is 31 January.
Is the late fee something the customer must pay?
Not necessarily. It is simple interest at a rate you choose, shown for information. Whether you can charge it depends on your agreement with the customer.
Which date should I use as the as-of date?
Today by default. Change it to see the position on another date.