Totalization agreement

Totalization agreements are concluded under §233 of the Social Security Act and are entirely separate from income-tax treaties — a country can have one and not the other. They do two things. First, they assign coverage to a single country under detached-worker and place-of-employment rules, so the same earnings are not charged social-security contributions twice; a certificate of coverage from the assigned country is the evidence. Second, they let periods of contribution in both countries be combined to qualify for a benefit that neither country's record would support alone. The practical consequence for a self-employed US citizen abroad is large: where the agreement assigns coverage to the foreign country, US self-employment tax does not apply to those earnings. The US has around thirty agreements in force, including Switzerland, France and Germany.