Invoice Late Fee Calculator
Calculate interest owed on an overdue invoice.
Enter your values
ⓘ Live results
Results
- Late fee owed
- $33
- Total amount due
- $3033
- Effective annual rate
- 18%
- Fee per day
- $1.5
Quick answer
Late fees are calculated by prorating the annual or monthly interest rate over the exact number of days overdue.
fee = invoice amount x monthly rate x (days late / 30)
How to use the Invoice Late Fee Calculator
- 1Enter the unpaid invoice amount.
- 2Enter the late fee rate stated in your contract, usually monthly.
- 3Enter days overdue to prorate the fee.
Worked example
Using the values the calculator loads with:
Inputs
- Invoice amount3000 $
- Monthly late fee rate1.5 %
- Days overdue22 days
Results
- Late fee owed$33
- Total amount due$3033
- Effective annual rate18%
- Fee per day$1.5
Frequently asked questions
What rate can I legally charge?
This varies by state/country — check local rules on maximum interest for late payments.
Does it compound?
This calculator uses simple proration; some contracts compound monthly, which grows faster.
About this calculator
- Built and reviewed by James Whitfield · How we build and test calculators
- Report an error
Results are estimates for general information. For medical, legal, structural or financial decisions, confirm with a qualified professional.