Work & Business
Invoice Late Fee Proration Calculator
A late charge should follow the written contract and applicable law. This calculator first reduces the invoice by any payment, removes the grace period, and prorates an annual simple rate over the remaining overdue days before adding a fixed fee. It is an arithmetic aid, not a determination that a fee is enforceable or tax-compliant.
Planning estimate only. Check measurements and real-world constraints before buying materials or making a commitment.
Calculate your scenario
Change any input. Results update immediately.
Your results
Estimated total late charge
$75.69
Prorated interest plus the scenario fixed fee.
Chargeable overdue days
37
Days overdue after the entered grace period.
Outstanding balance before fee
$3,600.00
Original invoice less payment received.
How the calculation works
The calculator applies this relationship to the inputs above. Keep every measurement in the unit shown.
Worked example
Use this example to check the calculator by hand before relying on a result.
Assumptions behind the result
- • Simple interest is used.
- • A 365-day year applies.
- • Payments reduce principal before the estimate.
- • The fixed fee is charged once after the grace period.
- • Contract and law are checked independently.
Mistakes that change the answer
- • Charging the original balance after payment.
- • Applying an annual rate as a monthly rate.
- • Adding a fee that the contract or law does not permit.