Can Charging Too Much Late Payment Interest Be Illegal?

Guides · Updated October 2026

Can charging too much late payment interest be illegal? The short answer is yes, but the longer answer is the one that actually protects you, so I will not leave it at yes. For a freelancer or small business charging interest on an overdue invoice, the risk rarely comes from a single national usury rate, because there is no single national rate for invoices. It comes from three quieter places: charging more than your own contract allows, charging a rate your state caps for that kind of debt, and calling something interest when a court would call it a penalty. Get those three right and a reasonable rate is usually defensible. Get one wrong and the whole interest claim can collapse.

Start with the contract, because it is the limit most people break without noticing. In Arizona, for example, the general statute allows parties to contract in writing for any rate of interest, but Arizona courts have held that the contract rate then becomes the legal limit: a lender who charges more than the contract allows forfeits all interest, not just the excess. The principle travels well beyond Arizona. If your contract says 1 percent per month, and you bill 2 percent per month because the client has been slow, you have not just overcharged by 1 percent. You have charged outside the agreement that justified the interest in the first place, and a court or a client dispute can treat the whole interest charge as unenforceable. The fix is boring and effective: charge exactly what the contract says, and if you want a higher rate, amend the contract before the next invoice, not after the client is already late.

State law is the second layer, and it is where people get tripped up by assuming their state works like another state. New York, for instance, has a general 16 percent per annum rule for loans and forbearances under General Obligations Law section 5-501, with exceptions for corporations and for larger amounts, but New York courts have treated a late charge on a delinquent account as something different from a loan or forbearance: a charge to cover the extra expense of late payment, not interest on a loan. That means a late fee in New York may exceed 16 percent per annum without being usury in the loan sense. Other states draw the line differently, and some states cap rates for specific kinds of debt, such as consumer credit, far lower than commercial rates. A rate that is lawful for a business to business invoice in one state can be unlawful for a consumer invoice in another. There is no shortcut here. Check the law for your state and your debtor type, or keep your rate modest enough that the question never gets litigated.

Can charging too much late payment interest be illegal when it is a late fee?

This is the distinction that decides many disputes, and it is worth slowing down for. Interest compensates you for the time value of money: the client held your money longer, so you charge for that time. A late fee compensates you for the extra cost of chasing payment: staff time, collection letters, disrupted cash flow. Courts in several states treat those differently. A late fee that reflects real extra cost is easier to defend than a late fee that is just interest wearing a different label. If you charge both a late fee and interest on the same invoice, make sure each one has its own basis in the contract, and make sure the combined total is not so high that it looks punitive rather than compensatory. A $25 late fee plus 1 percent per month on a $5,000 invoice reads as reasonable. A $500 late fee plus 2 percent per month on the same invoice reads as punishment, and punishment is what courts strike down.

Run the numbers on a concrete invoice so the risk is visible. A $10,000 invoice, 90 days overdue, at 1 percent per month simple interest, accrues $300 of interest. At 2 percent per month, it accrues $600. At 5 percent per month, it accrues $1,500 in 90 days, which annualizes to a rate most courts would look at closely, especially if the contract said something lower. The difference between the first and third figures is not just money. It is the difference between a client who pays with a grumble and a client who disputes the whole invoice, hires a lawyer, or reports the charge. High rates do not just risk a legal ruling. They risk the principal, because a disputed invoice gets paid later than an undisputed one, if it gets paid at all.

So what rate is safe? I will not give you a single number, because a single number would be wrong for half the states. Instead, use this test. First, is the rate in your signed contract, stated clearly, before the work started? Second, is it at or below the rates your state allows for this kind of debt, and have you checked that rather than assuming? Third, can you explain the rate as compensation for time and cost, not as a penalty for annoying you? Fourth, is the total, fee plus interest, proportionate to the invoice? If you can answer yes to all four, you are on solid ground. If you answer no to any one, lower the rate or fix the contract before you bill the interest.

One last trap deserves a mention, because it catches good faith people. Do not backdate a higher rate, do not add interest to an invoice that never mentioned it and then claim the client agreed by paying the principal, and do not charge interest on interest unless your contract explicitly allows compounding and your state permits it. Each of those moves turns a defensible interest claim into a dispute about honesty, and honesty disputes are harder to win than rate disputes. Charge what you agreed, document it, and let the calculator do the arithmetic. The interest is supposed to compensate you for waiting. It should not become the reason you wait longer.

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Related: Late Payment Interest Clause · Reasonable Late Payment Interest Rate · Simple vs Compound Late Payment Interest

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