Capital gains in the United States would be 15%.
People active in the world of finance often use bank accounts in different countries. Regions such as Belgium, Belize, and even Hong Kong do not have any capital gains for Bitcoin as of right now. Opening a bank account in that country and using it for Bitcoin exchange purposes is within the confines of the law. However, this activity will still be scrutinized by the government, and may result in an investigation regarding the origins of said funds.
There are also laws regarding owning a foreign bank account which should be taken into account if you decide to go this route.