Invoice Late Fee Calculator
Calculate interest owed on an overdue invoice.
Enter your values
Enter the invoice amount in $.
Enter the monthly late fee rate in %.
Enter the days overdue in days.
Results update instantly as you type — no submit needed. Your values are remembered on this device, and the shareable link reopens the calculator with exactly these numbers.
- Late fee owed
- $33
- Total amount due
- $3033
- Effective annual rate
- 18%
- Fee per day
- $1.5
Quick answer
Late fees are calculated by prorating the annual or monthly interest rate over the exact number of days overdue.
fee = invoice amount x monthly rate x (days late / 30)
At a glance
| What it does | Calculate interest owed on an overdue invoice. |
|---|---|
| Category | Business |
| Inputs needed | Invoice amount, Monthly late fee rate, Days overdue |
| Main output | Late fee owed |
| Formula | fee = invoice amount x monthly rate x (days late / 30) |
| Cost | Free — no sign-up, no download |
How to use the Invoice Late Fee Calculator
- 1Enter the unpaid invoice amount.
- 2Enter the late fee rate stated in your contract, usually monthly.
- 3Enter days overdue to prorate the fee.
Inputs explained
- Invoice amount($)
- Enter the invoice amount in $.
- Monthly late fee rate(%)
- Enter the monthly late fee rate in %.
- Days overdue(days)
- Enter the days overdue in days.
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.
What do I need to enter into the Invoice Late Fee Calculator?
Just 3 values: invoice amount, monthly late fee rate, days overdue. Every field starts with a realistic example, so you can change one number at a time and watch the result update instantly.
How does the Invoice Late Fee Calculator work out the answer?
Late fees are calculated by prorating the annual or monthly interest rate over the exact number of days overdue. It applies the formula fee = invoice amount x monthly rate x (days late / 30) and shows the working so you can check each step by hand.
Is the Invoice Late Fee Calculator free, and do I need an account?
It is completely free with no sign-up, no download and no usage limit. Everything is calculated in your browser, so the numbers you type never leave your device.
Results are estimates for general information. For medical, legal, structural or financial decisions, confirm with a qualified professional.