What is the best way to add interest to a customer's overdue invoice?

Hi @metzgertransport.

Welcome to the Intuit Community and thank you for reaching out here! QuickBooks is a flexible program that helps you to manage your accounting with ease. I'll be glad to share more information on adding interest to a customer's past due invoice.

At this time, there isn't the option to automatically add interest/late fees to invoices. However, you can manually add service fees to invoices. Here is a helpful guide for your reference. I can see how being able to automatically add lates fees to invoices would be beneficial for you. I recommend leaving feedback by heading to the Gear icon and selecting the Feedback option. These comments are viewed and considered by our developers as they create new features and updates for QuickBooks.

If you have any other questions, feel free to reach out to us here.