If you are a U.S. citizen or resident and you are self-employed in a country that does not have a Totalization Agreement with the United States, you may face the possibility of being subject to self-employment taxes to both the U.S. and the country where you are working.
U.S. self-employment tax applies to your net earnings from self-employment, including income earned abroad. The tax is composed of Social Security and Medicare taxes.
If your net earnings from self-employment exceed $400, you are required to file a U.S. tax return and pay self-employment taxes, regardless of where you live or work.
If the country where you are self-employed has its own social security system, you may also be required to contribute to that system. The specifics will depend on the country's laws and tax regulations.
Without a Totalization Agreement, there is no formal mechanism to prevent dual taxation on the same self-employment income. This means you could potentially be required to pay social security taxes to both the U.S. and the foreign country on the same earnings.
Know more about the Totalization agreement here: How Do Totalization Agreements Affect Your Expat Taxes?