If you work as an employee outside the United States, U.S. Social Security and Medicare taxes usually aren't withheld from your salary. However, there are certain exceptions. (Ex: You work abroad for an American employer). Instead, your foreign employer might withhold Social Security taxes under that country's system.
If you're self-employed outside the U.S., you'll still owe self-employment tax on foreign earned income. This is true even if you're able to claim the foreign earned income exclusion. However, agreements between the United States and many foreign countries may prevent you from being subject to self-employment taxes in both countries.
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