Hello Nunniyer,
Glad to learn you're using QuickBooks to help streamline your business. I'll be glad to share more invoicing in QuickBooks.
In order to accomplish your goal, you'll have to manually calculate the percentage and add it as a line item in $ amounts. I can see the benefit of having the option to add the late fee percentage and I encourage you to send feedback about this to our software developers. You can do this by clicking on the Gear icon and looking for Feedback.
In the meantime, feel free to ask other questions. I'm here to assist.
