Late Payment Calculator

Calculate the total amount owed on an overdue invoice, including accrued interest and flat late fees. Generate a polite payment reminder email ready to send.

Invoice Details

Invoice Amount

Currency Symbol

Invoice Due Date

Calculate As Of

Annual Interest Rate (%)

Applied as simple daily interest on the overdue balance.

Flat Late Fee (optional)

One-time fixed charge added on top of accrued interest.

Email Reminder Details

Your Name / Business

Client Name

Invoice Number (optional)

Preferred Payment Method (optional)

Calculation Results

Original Invoice Amount

Days Overdue

Daily Interest Rate

Accrued Interest

Flat Late Fee

Total Amount Due

Payment Reminder Email

How It Works

The calculator uses simple daily interest (not compound) applied to the original invoice amount:

Daily Rate   = Annual Rate / 365
Accrued Int. = Invoice Amount x Daily Rate x Days Overdue
Total Due    = Invoice Amount + Accrued Interest + Flat Fee

Days overdue counts from the due date up to and including the calculation date.
If the calculation date equals the due date, no interest is charged (0 days overdue).
The flat late fee is a one-time charge and is not compounded.
Check your jurisdiction's legal limits on late-payment interest before applying them to clients.

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