Hello there, @RangeRover, 

Calculating the subtotal item's quantity is only available in the Enterprise version. You can also add the Price and Cost columns when editing this item to reflect these on your invoice. Please see the screenshot for your reference. 

For more information about the different item types in the program, you can refer to this helpful article: Add, Edit, and Delete Items. 

Adding the Quantity column to calculate your subtotal's quantity in the lower versions of QuickBooks Desktop is a great idea. I want you to know that we are listening to your insights. Rest assured, I'll pass your suggestion to our product engineers so they can consider it for future updates. 

To help you stay up to date on all the product news and updates, I suggest visiting this article: What's New in QuickBooks Desktop for Windows 2019. Also, you can check out our helpful articles if you have other product-related questions in the future. 

You can count me in if there's anything else you need, @RangeRover. Have a nice day.