How does TurboTax determine if I have to report AMT?

The AMT is an "alternative" tax which TurboTax calculates behind-the-scenes, along with your regular federal tax. If the alternate method results in a higher tax than the regular method, you pay the difference on top of your regular tax.

Common reasons for getting hit with the AMT include:

• Exercising or selling ISOs (incentive stock options)
• Deducting interest from a large second mortgage for a house boat or recreational vehicle
• Realizing a large capital gain (for example, when you sell a home or other investments for a profit)
• Having a household income greater than the phase-out thresholds while also having a significant amount of itemized deductions

Instructions for Form 6251 (2022)

Thanks for the explanation on AMT. But that wasn't my question!

You mentioned "TurboTax calculates behind-the-scenes...". My question was if this behind-the-scene calculation is based on form 6251 (which seems to be the case per your response), shouldn't a copy of that form be included in the complete copy of full forms in PDF saved for my own records?

Yes, TurboTax creates a Form 6251 Worksheet. When you get ready to print your tax return, under What forms  would you like to generate?, select Tax Return, all calculation worksheets.  

• You may also select the 6251 worksheet and print it out. Select Specific Forms.

Great! Thanks. Yes, I can find/print the form selectively now that I look for it. But for whatever reason, it is not included in the PDF when I print by selecting Tax Return, all calculation worksheets, which is what triggered posting this question.