The Late Payment Penalty Generator
Calculate late fees and generate a professional notice PDF.
Late payment interest calculator + notice generator for freelancers with jurisdiction-aware rates (later).
Inputs
Calculate late fees and generate a professional payment notice.
Parties
Invoice
Dates & method
Notice notes
Result
Updated total due and ready-to-send notice.
What this tool does
The Late Payment Penalty Generator calculates interest on overdue invoices and generates a ready-to-send late payment notice. You enter invoice amount, due date, as-of date, and an annual interest rate, then the tool returns the late fee, updated total due, and a clean PDF report.
What you get
Days overdue, late fee amount, updated total due, notice text you can copy (plain or formatted), and a downloadable PDF report.
What it prevents
Inconsistent math, vague follow-ups, and emotional messages. This keeps your notice factual, procedural, and tied to clear numbers.
How the late fee is calculated
The tool first computes days overdue, then applies your selected method to calculate a late fee from the annual rate. If dates are missing or invalid, the tool shows an error and does not produce a late fee.
Step 1: Determine days overdue
Days overdue is the number of whole days between due date and paid or as-of date, clamped at zero. If the invoice is not overdue, the late fee is zero.
Step 2: Apply the annual rate
The annual interest rate is converted to a decimal rate and applied using one of three methods: simple interest, daily compounding, or monthly compounding.
Simple interest (pro-rated by days)
Late fee equals invoice amount multiplied by annual rate multiplied by days overdue divided by 365.
Daily compounding (365-day approximation)
Late fee equals invoice amount multiplied by (1 + annual rate / 365) raised to days overdue, minus 1.
Monthly compounding (month fraction approximation)
Days overdue is converted into months using days divided by 30. Late fee equals invoice amount multiplied by (1 + annual rate / 12) raised to months, minus 1.
Step 3: Updated total due
Updated total due equals invoice amount plus late fee. Values are rounded to two decimals for clean invoicing and notice text.
Key inputs, in plain language
This tool is designed to be practical. Most fields are optional for the notice, but the calculation needs valid dates and invoice amount.
Invoice amount
The original principal before any penalty. The late fee is computed from this base.
Due date and paid or as-of date
Due date is when payment was expected. Paid or as-of date is the date you are calculating up to. Use today’s date if you are preparing a notice before payment arrives.
Annual interest rate
The annual rate used to compute interest. The tool treats it as an annual percentage rate applied to the invoice amount.
Method
Choose simple interest for straightforward terms, or compounding when your agreement specifies it. Compounding in this tool uses practical approximations for daily and monthly methods.
Currency
Used for formatting values in the notice and PDF report.
Notes
A short payment request or instruction that appears inside the notice. If left blank, a neutral default line is included.
Turn the result into a clean follow-up
This tool gives you a consistent process: calculate, paste the notice, and send it without rewriting the story every time.
Copy and send the notice
Use Copy Text to send a plain version, or Copy Formatted to paste a rich version into email clients that support it.
Save scenarios
Save two scenarios on the device to compare outcomes, for example different interest rates or different as-of dates.
Export the PDF report
Download a PDF report that contains inputs, results, and a notice block. It is useful as an attachment or internal record.
Questions people ask before they send a notice
No. It is a calculation and notice generator based on user inputs. Use rates and terms that match your contract and local rules.
Use the date you want the calculation to run up to. If the invoice is still unpaid, use today’s date to generate the current total due.
Use simple interest unless your agreement clearly specifies compounding. Compounding produces higher fees as days overdue increases.
Daily uses a 365-day year and monthly uses a days-to-months conversion. These are practical approximations that keep the tool predictable and easy to explain.
Yes, but the late fee will be zero. The tool clamps days overdue at zero so you do not accidentally add penalties when the invoice is not late.