Most US businesses are owed money right now that they're too polite to chase. A clear late fee policy — stated upfront, calculated correctly — changes client payment behavior without damaging relationships.
What is a late fee on an invoice?
A late fee (also called a finance charge or interest penalty) is an additional amount charged when a client fails to pay by the agreed due date. It's standard practice, legal in all 50 US states, and one of the most effective tools for getting paid on time.
Most small business owners either don't charge late fees at all, or add them inconsistently. As a bookkeeper working with US clients daily, I see this constantly — and it costs real money.
What rate should you charge?
The US standard is 1.5% per month (18% APR). You'll see this on invoices from accountants, attorneys, consultants, and contractors across the country.
Most states allow up to 18% APR (1.5%/month) for commercial transactions. If you're billing other businesses — not consumers — 1.5%/month is safe in virtually every state. Check your state's specific rules for consumer invoices.
Alternatives to the standard rate
- Flat fee: A fixed dollar amount (e.g., $50 per month overdue). Simpler to explain to clients who aren't comfortable with percentages.
- Lower rate: Some service providers use 1%/month for long-term clients they want to protect.
- Tiered: 1.5% for 1–30 days late, 2% for 31–60 days. Increases urgency as time passes.
How to calculate late fees — step by step
The formula for simple (non-compounding) interest late fees:
For compounding interest, the balance each month includes the prior month's fee — meaning fees grow faster. Most small businesses use simple interest to keep it transparent and easier for clients to verify.
How to state late fees on your invoice
The most important rule: your late fee policy must appear on invoices before the work is done, not after an invoice goes overdue. Add this exact language to every invoice footer:
"Payment due within 30 days. A finance charge of 1.5% per month (18% APR) will be applied to all overdue balances. Overdue accounts may be subject to collection costs."
Put the same language in your client contract or engagement letter before work begins. If a client disputes the fee later and you never notified them, a court is unlikely to enforce it.
When and how to actually charge the fee
Step 1: Decide on a grace period
Many bookkeepers allow 5–10 days before charging fees. This is professional and reduces disputes with good clients who had a slow payment run. Document your grace period in your terms.
Step 2: Send a reminder first
Send a polite reminder at 7, 14, and 30 days overdue before adding fees. Most late payments are forgetfulness, not bad faith. Automation handles this well — most invoicing software (QuickBooks, FreshBooks) can do this automatically.
Step 3: Issue a new invoice with the fee
Don't modify the original invoice. Create a new invoice showing the original amount, the finance charge line item, and the new total. Reference the original invoice number. This creates a clean paper trail.
Step 4: Be consistent
If you waive fees for one client, do it deliberately — not as a default. Inconsistent enforcement makes your terms meaningless and teaches clients that due dates are optional.
What if a client refuses to pay?
In most cases you'll negotiate rather than pursue — the relationship usually matters more than $50. But know your options:
- If your terms were clearly stated and agreed to, the fee is legally enforceable
- For amounts under $5,000–$10,000, small claims court is an option in most states
- For larger amounts, a collections letter from an attorney often resolves it without court
Rather than doing this math manually every time, use the free Invoice Late Fee Calculator to get the exact amount with a month-by-month breakdown you can paste directly into a client email.
Disclaimer: This article provides general bookkeeping information and is not legal or financial advice. Late fee laws vary by state and transaction type. For significant amounts or disputes, consult a licensed attorney.