How is a late payment fee calculated?

It's either a flat fee or a percentage of the overdue amount, sometimes accruing per day or month based on the terms specified.

Are there legal limits on late fees?

Many jurisdictions cap allowable late fees for certain contract types, so check local regulations before setting a policy.

Does compounding matter for ongoing late fees?

Some structures compound (fees added to a growing balance) while others apply a flat fee each period — check which method applies.

Invoice Late Payment Fee Calculator

Find out how much interest or late fee applies to an unpaid invoice.

Invoice Amount ($)

Annual Late Fee / Interest Rate (%)

Days Late

Daily Rate -

Late Fee Amount -

Total Amount Due -

What Is the Invoice Late Payment Fee Calculator?

The Invoice Late Payment Fee Calculator estimates how much extra a client owes when an invoice is paid past its due date, based on a simple daily interest accrual of the annual rate stated on the invoice or contract.

Formula Used

Late Fee = Invoice Amount × (Annual Rate ÷ 365) × Days Late

This uses simple daily interest. Always check your contract or local regulations, as some jurisdictions cap late fees or require compounding.

How to Use This Calculator

Enter the original invoice amount.
Enter the annual late fee or interest rate agreed in your contract.
Enter how many days past the due date the payment is.
Click Calculate to see the fee and new total due.

Worked Example

A $2,500 invoice charges 18% annual interest and is 30 days late. Daily rate = 18% ÷ 365 = 0.0493%. Late fee = $2,500 × 0.000493 × 30 ≈ $37.00, making the total due about $2,537.00.