Invoice Late Fee Calculator
Calculate late payment fees and interest on overdue invoices.
Formula
Late Fee (flat) = Fixed Dollar Amount per occurrence Late Fee (interest) = Outstanding Amount × (Annual Rate / 365) × Days Overdue
How to Calculate
Late fees can be structured as a flat fee per occurrence, a percentage of the invoice amount, or daily/monthly interest on the outstanding balance. The most common approaches are a flat fee (e.g., $25–$50) for simplicity, or a periodic interest rate (e.g., 1.5% per month, which equals 18% annually).
For interest-based late fees, multiply the outstanding invoice amount by the annual interest rate, divide by 365 to get the daily rate, then multiply by the number of days the payment is overdue. Alternatively, divide the annual rate by 12 for a monthly rate if you assess interest monthly.
Before charging late fees, ensure they are clearly stated in your contract, engagement letter, or invoice terms. Many states have usury laws that cap the interest rate you can charge—typically 1–2% per month. Including late fee terms upfront sets expectations and provides legal standing to enforce them.
Worked Example
A $10,000 invoice is 45 days overdue. Your terms specify 1.5% monthly interest on late payments.
Monthly interest rate: 1.5% Daily interest rate: 1.5% / 30 = 0.05% per day Late fee: $10,000 × 0.05% × 45 days = $225
Or using annual rate: 1.5% × 12 = 18% annually Late fee: $10,000 × (18% / 365) × 45 = $221.92
Total amount owed: $10,000 + $225 = $10,225
Alternatively, with a flat $50 late fee: Total owed = $10,050.
Why It Matters
Late payments are one of the most common cash flow challenges for small businesses. On average, 61% of B2B invoices are paid late. Late fees incentivize timely payment, compensate you for the time value of money and collection effort, and establish professional boundaries. Even if you rarely enforce them, having late fee terms in place gives you leverage in collections conversations.
Practical Tips
- ✓State your late fee policy clearly on every invoice and in your contracts—it is difficult to enforce fees not agreed to in advance.
- ✓Check your state's usury laws to ensure your late fee rate is legally permissible.
- ✓Be consistent in applying late fees—selective enforcement undermines the policy.
- ✓Consider offering an early payment discount as a carrot rather than relying solely on late fee sticks.
Frequently Asked Questions
What is a reasonable late fee to charge?
Can I legally charge late fees?
Should I waive late fees for good clients?
Skip the Manual Calculations
FiscalInsights automates your financial calculations, tracks your metrics in real time, and gives you actionable insights to grow your business.
Start Free Trial