The simple estimate
The calculator uses a daily interest approach. This makes the result easy to understand and adjust before sending a reminder.
- enter the invoice amount
- choose or enter an annual rate
- count only the days after the due date
Interest and fees
How late payment interest estimates work
Interest calculations look precise, but the right rate depends on contract terms and local rules. Treat the calculator as a structured estimate, not a legal conclusion.
Overdue Invoice CalculatorFormula
Amount × annual rate ÷ 365 × overdue days.
Rate source
Use your contract or a verified statutory rule where available.
Review
Check whether flat fees, caps or notice rules apply.
Why local rules matter
Some jurisdictions use statutory rates, fixed recovery compensation or business-only rules. A number can be useful and still need review.
- check the contract first
- check the applicable country
- avoid adding fees you cannot justify
How to mention it
In early reminders, it is often enough to say that the amount may include agreed interest or fees where applicable.
- be specific when you have verified the basis
- separate principal, interest and fees
- keep the payment request clear
This guide is general information and not legal, tax or financial advice.