The agreement with Denmark became effective October 1, 2008.

Workers whose employment or self-employment would otherwise be covered by both the U.S. and Danish Social Security systems are covered and taxed by only one country's system beginning October 1, 2008. The agreement does not affect a worker's coverage prior to that date. If a worker had earnings before October 1, 2008 that were dually covered, those earnings would be subject to Social Security taxes in both countries.