Portugal requires 15 years of contributions for a contributory old-age pension, funded by a combined contribution of about 34.75% of salary (11% employee, 23.75% employer). With Portugal now one of the top European destinations for American remote workers and retirees, the agreement increasingly matters on the way in (avoiding double coverage) rather than only on the way out.
U.S. retirement benefits normally need 40 quarters (10 years) of credits. If you split a career between the U.S. and Portugal, you might fall short in each country alone. As long as you have at least 6 quarters of U.S. credits, the agreement lets you add your Portugal credits to reach eligibility — the U.S. then pays a benefit pro-rated to your U.S. credits only.
A Certificate of Coverage is the document that proves you're exempt from one country's social security. For U.S. coverage, the employer requests it from the SSA Office of Earnings & International Operations. Portugal's authority issues the equivalent when Portugal covers you.
Under the U.S.–Portugal agreement, a worker sent by a U.S. employer for 5 years or less normally stays under U.S. Social Security only and is exempt from Portugal's system. Your employer obtains a U.S. Certificate of Coverage as proof. Beyond 5 years, coverage shifts to Portugal.
Yes. If you have at least 6 quarters (about 1.5 years) of U.S. credits, the agreement lets you combine ("totalize") your U.S. and Portugal credits to reach the 40-quarter (10-year) threshold for a pro-rated U.S. retirement benefit.
The agreement has been in force since 1989.
Pension taxation depends on Portugal's domestic law and the separate U.S.–Portugal income tax treaty (if any), not the totalization agreement. The totalization agreement only governs which country's social security system covers you and how credits combine. Confirm pension taxation with a cross-border tax advisor.
It depends on how your work is structured. A U.S. employee formally posted to Portugal can generally remain under U.S. Social Security for up to 5 years with a certificate of coverage; a local hire or genuinely Portugal-based self-employed worker is normally covered by Segurança Social. Settle the classification and paperwork early — retroactive fixes are painful.