using turbo tax to do a pro forma return, using different income amounts

Since you say you are using Premier, I assume that you have the desktop (downloaded) TurboTax software installed on your computer. The quickest way to see the effect of different income amounts is to use the What-If Worksheet in forms mode. To get to the What-If Worksheet:

 

• Click the Forms icon at the top right.
• Click the Open Form icon at the top left.
• In the search box type "what" (without the quotes).
• The What-If Worksheet will appear in the window. Click on it,
  then click the Open Form button at the bottom of the window.
• Click Help Center for instructions for using the form.

 

The What-If Worksheet is not available in TurboTax Online.

If you prefer, you can create several different tax returns for different scenarios. Create one pro forma return and save it. Then you can make changes and save it with a different file name. You can repeat that process as many times as you want. But this is slower and more work than using the What-If Worksheet. Also, the What-If Worksheet lets you look at several variations side by side.