Basically, the long term cap gains rate is zero as long as your regular tax rate is at the 12% or 10% level, but once you hit the 22% tax bracket, your long term capital gains are taxed at 15%. For married filing jointly, the 22% bracket starts at $85,051. Then you add the standard deduction of $25,100.
So if your total income is less than $110,151, the part of that income that is LTCG would be tax-free. If your total income is more than that, you will start to pay tax on your LTCG.