Invoice Late Fee Calculator

Estimate statutory interest penalties and late fees for past due client invoices based on annual interest percentages and days late.

Input Details

Invoice Amount

The original amount of the outstanding invoice

Days Past Due Date

Number of calendar days since the invoice was due

Annual Late Fee Interest

Annual APR interest charge for late payments (default 8.0%)

Results

Late Fee Breakdown

Calculated Penalty Late Fee

$9.86

An annual interest rate of 8% accrues $0.33 in penalties every day. The total due is now $1,509.86.

Original Invoice Amount$1,500

Total Due (with Penalties)$1,509.86

Interest Accrual Rate$0.33/day

The Formula

Formula Overview:

1. Late Fee = Invoice Amount × (Annual Late Rate ÷ 100) × (Days Late ÷ 365)
2. Daily Accrual Rate = (Invoice Amount × (Annual Late Rate ÷ 100)) ÷ 365
3. Total Outstanding Due = Invoice Amount + Late Fee

Example Calculation

If your invoice is for $1,500, it is 30 days past due, and your contract specifies an annual interest rate of 8%:
Annual Interest: $1,500 × 0.08 = $120.00 /year | Daily Rate: $120.00 / 365 = $0.329 /day Late Fee (30 days): $0.329 × 30 = $9.86 | Total Due: $1,500 + $9.86 = $1,509.86

How to Use This Calculator

Enter the original **Invoice Amount** that is past due.
Input the total number of **Days Late** past the original due date.
Input the **Annual Interest Percentage** stated in your contract (standard commercial rate is typically 8-10%).
Review the daily accrual rate and total outstanding fee.

When This Calculator is Useful

Use this calculator when **sending payment reminders to late clients**, accounting for unpaid company receivables, or reviewing cash flow losses due to delayed client payments.

Disclaimer Note

All results are estimates based on standard business formulas and rates. Actual project costs, ROI, and rates may vary based on market conditions, specific requirements, and contract agreements.

Frequently Asked Questions

Late payment interest is typically calculated as an annual percentage rate (APR) prorated by the number of days the invoice is past its due date. The standard formula is: Invoice Amount × (Annual Interest Rate ÷ 100) × (Days Late ÷ 365).

Standard business-to-business interest rates typically range from 5% to 12% per year. Many jurisdictions have statutory limits (e.g. the UK Late Payment of Commercial Debts Act allows charging 8% plus the Bank of England base rate). Self-charging fees above 15% can sometimes be legally contested as punitive penalties.

It depends on your local laws, but in many regions, commercial statutory laws allow you to charge reasonable interest on late business transactions even without a contract clause. However, it is always best practice to outline your payment terms (e.g. Net 30) and late fee interest clauses clearly in your signed client contracts.

Keep the tone firm, polite, and professional. State the invoice number, due date, original amount, and the calculated late fee. Attach a copy of the original invoice and the signed agreement. Offer a clear payment link and ask them to confirm receipt of the email and state their payment ETA.