Hi langesmn!

Good news for you because QuickBooks has a feature that automatically calculates late fees or finance charges on overdue invoices. It can be a fixed amount or a percentage of the remaining balance per invoice, week, or month.

Once set up, the condition will be applied to future invoices that become overdue and exceed the grace period. They will have an additional late fee item, and their balances will be updated. All you need to do is send the updated invoice to your customer to make them aware that a late fee has been added to their invoices. Please check out this article for more information: Apply late fees to overdue invoices automatically in QuickBooks Online.

To enable to feature:

1. Go to the Gear icon and choose Accounts and settings.
2. Choose Sales and click the Late fees section.
3. Click the Switch icon and set the conditions. The instructions are straightforward, but let me know if you have questions.
4. Click Save, and then Done.

If you don't want to send out updated invoices manually, you can enable the Reminder feature and set strategic date of when to send a reminder. For example, if your invoice has a 5-day grace period, you can set the invoice reminder to be sent 6 days after the due date.

Let me know how I can help you handle late fees further, so we can make the most of the feature. Have a good one!