Can QBO be set up to charge interest on overdue accounts?

Hi there, @zimmjoa.

Are you referring to your customer's overdue invoices? If that's the case, you have two options to charge interest to your customers. I'll share with you how.
 

First, you can create a separate invoice for the charge.  If you haven't yet, I recommend creating an interest item following these steps:

1. Sign in to your QuickBooks Online (QBO) account.
2. Go to the Gear icon, then choose Products and Services.
3. Click New.
4. Choose either Non-inventory or Service.
5. Enter a desired name of the interest.
6. Choose the Income account, then click Save and close.

Now, here's how you can add the item on the new invoice:

1. Go to the +New icon, then select Invoice.
2. Under the PRODUCT/SERVICE column, add the interest item.
3. Enter the amount manually in the AMOUNT tab.
4. Tap on Save and close.

The second option is to add the charge on the existing invoice.

1. Click Sales, then go to the Customers tab.
2. Choose the customer, then look for the past due invoice.
3. Add the interest item in the unused line, then enter the amount.
4. Hit Save and close.

For more tips about handling your invoices in QuickBooks, you can open this article: Create invoices in QuickBooks Online.

Additionally, you can get more hints while handling your other customer entries in the future by opening the topics from this link: Topics about your company's income and customers.

If you're referring to something else, please let me know by adding a comment below. I'll get back to your as soon as I can help you again. Have a good one!