ASSUMING for the moment that your taxable income is below the top dollar amount where LTCGs are taxed at 0%, you will pay 0% on that LTCG as long as the sum of your other taxable income and the LTCG remain below the threshold. But the moment that sum exceeds the top dollar amount the additional LTCG will be taxed at the next higher LTCG rate of 15%. So ultimately it's possible to pay 0% on some of the LTCG and pay 15% on the rest of the LTCG.
