If you are a self-employed U.S. citizen or resident, the rules for paying self-employment tax are generally the same whether you are living in the United States or abroad.
Generally, self-employed taxpayers must file a US income tax return if net earnings from self-employment were $400 or more.
Self-employment income is income that arises from the performance of personal services, but which cannot be classified as wages because an employer-employee relationship does not exist between the payer and the payee. The Internal Revenue Code imposes the self-employment tax on the self-employment income of any U.S. citizen or resident alien who has such self-employment income.
Self-employed individuals generally must pay self-employment tax as well as income tax. Self-employed tax is a Social Security and Medicare tax primarily for individuals who work for themselves. It is similar to the Social Security and Medicare taxes withheld from the pay of most wage earners. Your payments of these taxes contribute to your coverage under the U.S. social security system.
The self-employment tax rate is a percentage set by law of your net earnings from self-employment. This rate consists of 12.4% for social security and 2.9% for Medicare taxes for 2013. The maximum amount of net earnings subject to the social security tax is set by law and changes annually. All of your net earnings are subject to the Medicare tax. For 2014, the maximum amount of net earnings from self-employment that is subject to the social security portion of the tax is $106,800. All net earnings are subject to the Medicare portion of the tax.
Self-employed expats may exclude all or part of their self-employment income through the foreign earned income and housing exclusions. However, they still are responsible for the self-employment taxes unless there is a social security agreement between the host country and the US.