How do I charge fixed late fees for the customer?

To charge a fixed late fee (rather than a finance charge based on an annual interest rate), create an "other charge" item for the fee, and assign the item to an income account called Late Fee Income. You can then use this item to charge your customers any fixed amount, by using it as a statement charge in the customer's register or as a line item on an invoice.

If you wish, you can also send a reminder statement or reprint an invoice as a late notice. You may want to change the statement or invoice title to "Late Notice." See Customizing invoices or statements.