Can You Charge Interest on Overdue Invoices? (Yes — Here's How)

Yes, you can charge interest on overdue invoices — but only if your agreement with the client established the right to do so before the invoice was issued. You cannot add interest retroactively to an invoice that was sent without any mention of late charges. The legal basis for charging interest on a business invoice is contractual: the client agreed to the terms when they signed your contract, accepted your proposal, or received your invoice with the terms clearly stated. This is not a legal advice article, and you should consult a qualified attorney for guidance specific to your situation, but the general principle is well-established across US jurisdictions.

The most common way to establish the right to charge interest is to include a late payment clause in your contract or service agreement. The clause should state the interest rate (typically expressed as a monthly rate, such as 1.5 percent per month), when interest begins accruing (usually the day after the due date), and how it is calculated (on the outstanding principal balance). If you do not have a formal contract, you can include the same language in your standard invoice template. The key is that the client sees the terms before you invoice them, not after the invoice is overdue.

Typical late payment interest rates for service businesses in the United States range from 1 to 2 percent per month, or 12 to 24 percent per year. Some businesses use a flat late fee instead of a percentage — for example, a $50 or $100 fee per month the invoice remains unpaid. Either approach is legally defensible if disclosed in advance. Be aware that some states have usury laws that cap interest rates on commercial transactions. The caps vary by state and by the nature of the transaction; a few states have no cap for commercial debts, while others set limits in the range of 10 to 18 percent per year. Checking your state's commercial usury limits before setting your rate is advisable.

Adding accrued interest to an overdue invoice in practice means sending a revised invoice or a separate statement that shows the original balance, the number of days past due, the applicable rate, and the interest amount added. Many accounting systems can calculate and add this automatically if you configure late fee rules. Sending a revised invoice with the accrued interest included gives the client a clear, updated balance and reinforces that the late payment clause is active and being enforced.

In practice, many small businesses include interest clauses in their contracts but rarely enforce them rigorously — either because they are concerned about the relationship or because the administrative overhead of tracking and billing accrued interest is not worth the recovered amount. The more common use case is as a deterrent: clients who know they will accrue 1.5 percent per month on overdue balances are more motivated to prioritize payment than clients who face no stated consequence for lateness. Whether you choose to enforce the clause aggressively or use it primarily as a deterrent, having it in your contracts costs nothing and gives you options.