Free tool

Late fee calculator

Work out how many days an invoice was paid late and what late fee that adds up to, as a flat fee or as a monthly interest rate. Free, no sign-up, and the calculation runs in your browser.

Result

Days late

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Late fee

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Total with late fee

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Check the rules that apply to you

Limits on late fees and interest differ from state to state and can depend on the type of customer and on your contract. Put your late fee terms in writing on your invoices or agreements before you charge them, and check your state and local law or ask a professional. This calculator is for estimates only and is not legal advice.

Let late fees and reminders run themselves

NartPay OS can add a late fee for you: after the grace period you choose, it creates one late-fee invoice for each overdue invoice, as a flat amount or a percentage of the balance, either as a draft to review or sent automatically. Payment reminders by e-mail are built in too.

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Late fees: common questions

How is a monthly late fee calculated?

With simple interest, multiply the unpaid amount by the monthly rate, then by the share of a month the payment was late. This calculator turns the monthly rate into a yearly rate (× 12) and charges it per day (÷ 365). Interest is not added on top of earlier interest.

Flat fee or percentage?

A flat fee is easy to understand and the same for every invoice. A percentage grows with the amount and the delay, so it suits larger invoices. Whichever you choose, state it clearly before the work starts.

What is a grace period?

A few days after the due date during which you do not charge a late fee. It covers payments that are already on their way and keeps relationships friendly. If the payment comes after the grace period, you can count the fee from the due date or from the end of the grace period.

How do I avoid late payments in the first place?

Send invoices right away, state the due date and your late fee terms on every invoice, make it easy to pay online, and send a friendly reminder before and after the due date.

Late fee calculator

Invoice

Late fee terms