To leave America, you generally must prove 5 years of U.S. tax compliance. If you have a net worth greater than $2 million or average annual net income tax for the 5 previous years of $157,000 or more for 2014 (that’s tax, not income), you pay an exit tax. It is a capital gain tax as if you sold your property when you left. At least there’s an exemption of $680,000 for 2014. Long-term residents giving up a Green Card can be required to pay the tax too.
Now, the State Department interim rule just raised the fee for renunciation of U.S. citizenship to $2,350 from $450. Critics note that it’s more than twenty times the average level in other high-income countries. The State Department says it’s about demand on their services and all the extra workload they have to process people who are on their way out.
The expatriation tax provisions under Internal Revenue Code (IRC) sections 877 and 877A apply to US citizens who have renounced their citizenship and long-term residents (as defined in IRC 877(e)) who have ended their US resident status for federal tax purposes. Different rules apply according to the date upon which you expatriated.