How to Calculate Invoice Aging

Invoice aging shows how long an unpaid invoice has been outstanding, making it easier to review receivables and follow up consistently.

What is invoice aging?

Invoice aging measures the time between an invoice's due date and today, or another review date. An invoice that has not reached its due date is current. Once the due date passes, the number of days overdue increases as time passes.

Calculate days overdue

A simple calculation is days overdue = review date − invoice due date. If the result is zero or negative, the invoice is not overdue on that review date. If it is positive, the result is the number of days past due.

Use aging buckets

Businesses often group unpaid invoices into ranges such as current, 1–30 days overdue, 31–60 days, 61–90 days, and more than 90 days. The exact buckets can vary by business. The purpose is to make older receivables easy to identify and review.

Review the amount as well as the age

Age alone does not tell you which invoice matters most. Review the outstanding amount, client relationship, payment history, agreed terms, and any documented dispute alongside the age of the invoice.

Connect aging to your follow-up process

Use clear payment terms and send invoices promptly. When an invoice becomes overdue, check the invoice and payment status first, then send a factual reminder. Keep records of follow-up and escalate according to your agreed process.

Invoice aging is different from a late-payment fee

Days overdue can be used as an input for a late-payment calculation, but an aging report does not establish that a fee or interest is legally owed. Check the contract, invoice terms, and applicable rules before charging a late fee.

Related guides

How to Follow Up on an Overdue Invoice · Invoice Payment Terms · How to Get Paid Faster as a Freelancer · How to Number Invoices

Planning note

This guide provides general business information. Invoice terms, late fees, interest, and collection requirements can vary by contract and jurisdiction.