QB Issue Resolution:

QuickBooks Online does not have the ability to automatically calculate finance charges or late fees on open invoices at this time. Also, there is not a separate area on invoices for service charges or late fees. To assess an additional fee of this type, you must either create a separate invoice for the charge or include it as another line item on your invoice.

To include an additional charge as you create a new invoice:

Go to the (+) icon and select Invoice.
Fill out the invoice as usual, including the applicable products/services.
In the next unused line select the Product/Service item for service charges or late fees, or choose Add New under Product/Service and follow the prompts if an item for this type of fee has not yet been set up. You can call it Finance Charge (or whatever fits best).
Enter the amount of the charge.
Save.

Resolution for Issue 'How come the online version of QB does NOT calculate finance charges, as the desk top version does. When are you going to have this available. One of the' available: Yes (Solved).
Source: Intuit Community forum.

How come the online version of QB does NOT calculate finance charges, as the desk top version does. When are you going to have this available. One of the: this issue or error code is a known issue in Quickbooks Online (QBO) and/or Quickbooks. Support for this issue is available either by self-service or paid support options. Experts are available to resolve your Quickbooks issue to ensure minimal downtime and continue running your business. First try to resolve the issue yourself by looking for a resolution described below. If it is a complex issue or you are unable to solve the issue, you may contact us by clicking here or by using other support options.

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