Clarification: That individual/taxpayer is a US citizen living in the United States and the retirement income he receives is for twenty years of work in Poland before he migrated to the US. He never worked in Poland as a US citizen. Currently, as a US citizen, he is subject to worldwide income. Had he worked in the United States for forty years, his entire Social Security benefits would have been entered on line 6a, and treated preferentially, meaning non-taxable at all, or partially taxable, but maximum 85% includable in income. Since part of the same kind of income is being received from another country, does that change the tax treatment of Polish Social Security?