It's my first time paying AMT (due to receiving a chunk of backpay early in 2017).  

I noticed that on the Tax Summary, turbotax has added "other taxes" of $156. After a LOT of searching, I found that most of this amount is equal to 0.9% x my income that is above $200,000.  

This is the Additional Medicare Tax that applies to wages/income >$200K for single filer. 

The problem is that my w2 form shows that my employer has already withheld the additional amount of medicare tax.  My employer withheld 1.45%x$200,000 PLUS 2.35%x ($217,333-$200,000) or $3307, from my paychecks.

It looks like turbotax is making me pay the extra 0.9% TWICE!  

If I already paid it (through withholding on my paychecks) why would I have to pay it again?

Is this an error in turbotax?

Please advise...