If both the U.S. and Japanese social security systems cover a worker's employment
or self-employment, the Agreement provides that beginning October 1, 2005, only one
country's system will cover the worker's employment or self-employment. The Agreement
does not affect a worker's coverage prior to that date.
If a worker had dually covered earnings before October 1, 2005, those earnings remain
subject to social security taxation in both countries.