Totalization agreements decide which country’s social security system a cross-border worker pays into and let contribution periods count toward benefits in both. The US–Spain agreement is why an American employee in Madrid can stay in one system; the absence of a US–Türkiye agreement is why a self-employed American in Istanbul keeps paying US self-employment tax with no certificate-of-coverage exit — a cost line the “0% tax in Turkey” posts omit.
Totalization agreement
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