CleanUtils

Invoice Late Fee Calculator

Calculate overdue invoice fees from amount, due date, flat fee, monthly rate, and as-of date.

Also useful for: invoice late fee calculator late payment fee calculator overdue invoice interest invoice penalty calculator Invoice Late Fee Calculator

Invoice Late Fee Calculator

Runs in your browser. Inputs are not uploaded.
Input
Results 
Summary: 17 days late. Estimated late fee: $35.20.

Stats
- Days Late: 17
- Fee: 35.20

Issues
- Note: This is arithmetic only, not legal, tax, or collections advice.

Output
Invoice amount: $1200.00
Days late: 17
Flat fee: $25.00
Interest: $10.20
Total late fee: $35.20
Amount plus fee: $1235.20

Invoice Late Fee Calculator Example Run

Estimate an overdue invoice fee from simple terms.

Sample inputs
Invoice
Invoice amount: 1200
Due date: 2026-04-01
As of: 2026-04-18

Fee terms
Flat fee: 25
Monthly rate: 1.5

Generated result
Summary: 17 days late. Estimated late fee: $35.20.

Stats
- Days Late: 17
- Fee: 35.20

Issues
- Note: This is arithmetic only, not legal, tax, or collections advice.

Output
Invoice amount: $1200.00
Days late: 17
Flat fee: $25.00
Interest: $10.20
Total late fee: $35.20
Amount plus fee: $1235.20

What the Invoice Late Fee Calculator Checks

  • Invoice amount

    The original invoice amount is used as the base for interest calculations.

  • Days late

    Due date and as-of date are compared to calculate overdue days.

  • Flat fee

    A one-time late fee can be included when the invoice is overdue.

  • Monthly interest

    Monthly percentage interest is prorated by days late.

  • Advice caveat

    The report is arithmetic only and includes a legal/tax/collections disclaimer.

Invoice Late Fee Calculator Questions

  • Q: Does the invoice late fee calculator upload my invoice details? A: No. Inputs are processed in your browser, and pasted content is not sent to analytics or a server.
  • Q: What should I paste into the invoice late fee calculator? A: Enter invoice amount, due date, as-of date, flat fee, and optional monthly interest rate.
  • Q: What can I copy or download? A: You can copy the fee breakdown as plain text.
  • Q: What does the invoice late fee calculator not verify? A: It does not determine whether a fee is legally allowed, calculate taxes, send notices, or replace accounting advice.

Related Tools

Updates

  • v1.0.0 New 2026-05-17: Initial overdue-day, flat-fee, and prorated monthly interest calculator added.

Use Invoice Late Fee Calculator with an LLM

Copy the prompt or pass the llms.txt contract link to your assistant.

Prompt 
Use the CleanUtils Invoice Late Fee Calculator tool for this request.
Tool contract: https://cleanutils.com/business-tools/invoice-late-fee-calculator/llms.txt

Read the llms.txt contract, ask me for any missing required input, then follow the contract exactly. If the contract includes JavaScript, run `runCleanUtilsTool(userInput)` in a sandboxed JavaScript runtime and return the result with any warnings or errors.
llms.txt https://cleanutils.com/business-tools/invoice-late-fee-calculator/llms.txt