Late Fee Calculator

How late fees work

A late fee is an extra charge added to an invoice when a client pays after the due date. Its purpose is to compensate you for the delay and to encourage prompt payment. The fee is calculated from the number of days an invoice is overdue - counted from the due date to the date the client actually pays (or is expected to pay).

To estimate a fee, you need three things: the outstanding amount, the due date, and the payment date. From there you decide how the penalty is structured.

Flat vs percentage, and per-month vs one-time

There are two common ways to structure a late fee:

• Flat fee - a fixed amount, such as a set administrative charge, applied once the invoice becomes overdue.
• Percentage fee - a percentage of the outstanding balance, commonly 1%-2%. This scales with the size of the invoice, so it feels fairer on both small and large amounts.

You also choose how often the fee applies. A one-time fee is added once, no matter how long the invoice stays unpaid. A per-month fee accrues for each month (or part of a month) the invoice remains overdue, so the penalty grows the longer the client waits. Per-month percentage fees behave like simple interest on the balance.

When you can legally charge a late fee

A late fee is only enforceable if your client agreed to it before the debt arose. That agreement usually lives in your contract, your terms of service, or a clearly stated clause on the invoice itself - for example, "A late fee of 2% per month applies to overdue balances." Without prior agreement, you can request the fee but may not be able to enforce it.

Many regions also cap the maximum interest or penalty you can charge, and some have statutory late-payment rules for business-to-business invoices. Keep your rate reasonable and check the limits that apply where you and your client operate.

Communicate late fees up front

• Include the late-fee policy in your contract before work starts.
• Print the policy and the due date clearly on every invoice.
• Remind clients of the policy in a friendly way before the due date - the payment reminder generator can help.
• Apply the fee consistently so it never feels arbitrary.

Practical tips

• Use a short grace period (a few days) before the fee kicks in to preserve goodwill.
• Set realistic due dates so clients have a fair window to pay.
• Waive the fee occasionally for reliable clients - flexibility can be worth more than the penalty.

Disclaimer: This tool provides an estimate only and is not legal or financial advice. Late-fee and interest rules vary by region and by contract. Confirm what you are allowed to charge before applying a fee.