What is the Alternative Minimum Tax (AMT)?
As the name says, it's an "alternative" tax which we calculate behind-the-scenes, along with your regular federal tax. If the alternate method results in a higher tax than the regular method, you'll pay the difference on top of your regular tax.
AMT calculations are too complicated to explain here. If you're really interested, you can fill out Form 6521 according to the 6521 instructions; your AMT amount, if any, will appear on line 35 of the 6521 (or you can just let TurboTax figure it for you).
For tax year 2017, the AGI thresholds subject to the AMT start at $54,300 (single and head-of-household), $84,500 (married filing jointly), and $42,250 (married filing separately). Next year, as a result of tax reform legislation, the AGI thresholds increase to $70,300 (single, HOH), $109,400 (MFJ), and $54,700 (MFS).
Based on what you've entered into your return, we'll let you know if you are subject to the AMT, which will transfer to line 45 of your 1040 form. We'll also add Form 6251 to your return. Your final refund/taxes owed amounts will already include the AMT – you don't pay it separately.