The highest federal marginal capital gains tax rate in the United States sits at 20 percent for long-term capital gains applicable to high-income earners exceeding specific annual statutory threshold limits. When combining this top bracket with the 3.8 percent Net Investment Income Tax (NIIT) levied on high earners, plus applicable state income taxes, the total effective tax burden on investment profits can approach or exceed 30 to 37 percent depending on the state of residence.