Sorry I missed your drift regarding a TurboTax professional. I've had mixed results with phone calls. Realizing that the person is caught cold with your question is a challenge. A written response is better and provides a history.
A new posting would be interesting but given no responses to this, that may not happen.
If you are trying for an answer to make a sale before 12/31, that might be a stretch. Hopefully dmertz will reply. He is the sharpest I've found.
Bottom line using your example, I see the following:
250,000 LTCG not subject to NIIT plus, I believe, your exposure for selling half is the 50,000 of LTCG + the 3.8% NIIT on the 50,000.
At a 15% LTCG tax rate:
15% x 250,000 = 37,500
15% x 50,000 = 7,500
3.8% NIIT = 1,900 NITT for the 50,000.
Total = 46,900
Does not include other taxable income
