Late Payment Calculator
Work out interest and fees for overdue invoices.
Interest due
$0.00
Late fee
$0.00
Total due
$0.00
What this tool does
Calculate how much an overdue invoice grows when you apply a late payment interest rate and a one-time late fee. Use the result to send an accurate, professional reminder instead of guessing.
How to use it
- 1Enter the original invoice amount.
- 2Add the number of days the invoice is overdue.
- 3Set an annual interest rate (for example 8% per year) and an optional flat late fee.
- 4The calculator shows the interest due, the fee, and the new total.
Worked example
A $1,000 invoice that is 45 days overdue at 8% annual interest with a $20 late fee → interest ≈ $9.86 + $20 fee = $1,029.86 due.
Frequently asked questions
Can I charge interest on late invoices?
Only if your contract or payment terms allow it — and local rules vary by country. Mention the rate on your invoice and in your agreement so the client has agreed to it up front.
How much interest can I charge?
There is no universal answer. Some jurisdictions set a legal default rate (such as a statutory rate linked to the central bank), while others prohibit interest without a written agreement. Check your local rules before applying a rate.
Is a flat late fee better than interest?
A flat fee is simpler to communicate and enforce. Interest better reflects the real cost of waiting for money. Many businesses use a combination of both, set out in writing.
Turn the result into a real invoice
Create a professional PDF from your numbers in under two minutes.
Create an invoice