I have a taxable income in $252K... do i need to pay Alternative minimum taxes ? is there a threshold of $250K and i have to pay over the excess [$2K]?

The TT program will automatically compute any AMT taxes if you need to pay them.  

Good news: The number of taxpayers subject to the AMT is expected to drop dramatically in tax years 2018 through 2025, due to higher exemptions and phase-out thresholds. The AMT calculation is complicated. Review Form 6251 Alternative Minimum Tax - Individuals for the exact calculation.

See How will tax reform affect my 2018 federal tax return?

How is AMT calculated? 

The AMT calculation is complicated and beyond the scope of this article, but here’s an outline of how it works:

1. We start by figuring your AMT income (your AMTI) by adding certain deductions back into to your AGI. (This is the part that’s too complicated to explain here.)
2. Then we subtract your AMT exemption from your AMTI.
3. The result is then multiplied by the AMT tax rate to come up with your alternative tax.
   • If your alternative tax is less than your regular tax, you’re exempt from paying it (most taxpayers fall into this group).
   • If your alternative tax is more than your regular tax, you have to pay the difference. We account for this in your final tax refund or taxes owed amount – you don’t pay it separately.

Related Information:

• Why am I getting hit with the AMT (Alternative Minimum Tax)?
• How much is the AMT exemption?

if your subject to AMT form 6251 will be in your return. amt is on line 11 of the form and transfers to schedule 2 line 1