To find the AGI calculated on the current year return, click on the "forms" icon on upper right of the screen and select the Form 1040 or whatever form version you are using. AGI is line 11 on Form 1040. Might be a different line for other forms but it will be on the 1st page.
To find your previous year's AGI, entered for identification purposes, go the the step by step and click on the "File" tab. Continue a few screens in to find where it asks for your AGI. If you already entered AGI, you will see what you entered there.
