What's a Reasonable Invoice Late Fee?

There's no federally mandated late fee for business invoices — it's a contractual matter you and your client agree on. That said, clear norms exist: 1–1.5% per month (roughly 12–18% annually) is the most common B2B practice, chosen partly because it comfortably stays under most states' usury law caps while still motivating prompt payment.

The Three Common Fee Structures

Percentage-based fees scale naturally with invoice size and work well for ongoing client relationships. Flat fees are simpler to communicate and common for smaller, fixed-price invoices where a percentage would be trivial.

How to Use This Calculator

Enter your invoice amount and how many days it's overdue. Pick the fee structure that matches your contract terms — most businesses use a monthly percentage. The calculator shows the fee amount, new total due, and the equivalent annual rate so you can sanity-check it against usury limits.

Why Disclosure Timing Matters

Late fees are only enforceable if the client agreed to them before the work began — typically in your contract, statement of work, or the original invoice terms. Adding a late fee retroactively to an invoice the client never saw the terms for is legally shaky and often unenforceable. Always state your policy upfront: due date, grace period (if any), and the exact fee or rate that applies.

Usury Laws: The Limit You Can't Ignore

Every state sets a maximum interest rate (the "usury limit") that applies to late payment charges. Common B2B ranges run 12–24% annually depending on the state, with stricter limits often applying to consumer transactions than business-to-business ones. Charging an excessive rate risks the fee being void or unenforceable even if your client agreed to it — when in doubt, staying at or below 1.5%/month (18% annually) is a generally safe, widely used benchmark.

Simple vs. Compounding Interest

• Simple interest: the fee is calculated on the original invoice amount each period — the standard, more client-friendly approach
• Compounding interest: each new fee is calculated on the growing balance (invoice + previous fees) — grows faster, and some states restrict or prohibit it

This calculator uses simple interest for the percentage-based modes, the more common and more defensible structure.

Worked Example

A $2,500 invoice, 45 days overdue, at a 1.5% monthly rate: the late fee comes to about $187.50 (1.5% × 1.5 months), bringing the new total to $2,687.50 — an effective annual rate of 18%, comfortably within typical B2B usury limits.

Beyond the Calculator: Reducing Late Payments

A late fee is a backstop, not a strategy. Sending invoices promptly, offering an early-payment discount, making payment easy (multiple methods, one-click links), and following up professionally before the due date all reduce how often you need to apply a late fee at all.

Where This Fits Your Bigger Picture

If chronic late payments are affecting your cash flow planning, check our freelancer hourly rate calculator to make sure your rates account for the admin cost of chasing payments, and our break-even calculator for broader cash flow planning.

Frequently Asked Questions