Finland runs two layers: the earnings-related työeläke (TyEL), which accrues about 1.5% of each year's earnings with no minimum vesting period, and Kela's residence-based national pension as a floor. The agreement coordinates U.S. Social Security with this structure and prevents double contributions for posted workers.
U.S. retirement benefits normally need 40 quarters (10 years) of credits. If you split a career between the U.S. and Finland, 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 Finland 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. Finland's authority issues the equivalent when Finland covers you.
Under the U.S.–Finland 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 Finland's system. Your employer obtains a U.S. Certificate of Coverage as proof. Beyond 5 years, coverage shifts to Finland.
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 Finland credits to reach the 40-quarter (10-year) threshold for a pro-rated U.S. retirement benefit.
The agreement has been in force since 1992.
Pension taxation depends on Finland's domestic law and the separate U.S.–Finland 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.
For the earnings-related työeläke, effectively no — rights accrue from your first insured earnings and are payable to the U.S. at retirement. The residence-based Kela national pension has its own residence requirements, but the earnings-related layer alone means short Finnish careers still produce real money.