Welcome to the Online Community. I’ll be sure to point you in the right direction about adding interest charges on the statement.
Since there’s not a direct way of adding these items on a statement, you can either create a separate invoice or add the charges on an existing invoice. To begin, create the interest charges item in your account.
Go to the Gear icon at the top, and select Products and Services.
In the Products and Services window, select New.
Select the product or service type.
Enter the name such as Interest charges.
Fill in the field boxes.
Once done, click on Save and close.
To record the charges, check out this article for the step by step process: How to enter late fees on invoices. Once you create a statement, the interest amount will automatically show on the transaction.
I've attached an article that will help manage your statements efficiently: Create Statements.
By following the resolution steps,you'll be able to see the interest charges added on the statement.
Feel free to leave a comment below if you have questions about working QBO. I'll be around to help. Have a great rest of your day.