The Arctic is a highly seasonal environment with a harsh climate and extensive sea ice cover during the winter. Consequently, most Arctic-breeding seabirds migrate south to reach more benign environmental conditions. Knowledge of migration routes and wintering areas is integral for successful conservation of these globally important breeding populations. In this study, we deployed light-level geolocators on female common eiders Somateria mollissima breeding in Kongsfjorden, Svalbard, to track movements during the non-breeding season. We retrieved functioning loggers from 47 individual birds in 2009–2013 and mapped their migration routes and wintering areas. Thirty-six birds (77 %) wintered around the Icelandic coast and 11 (23 %) off the coasts of North Norway. Autumn migration took place between late August and late December, and spring migration from late March to late May. The migration (ca 1700 km to Iceland and 1300 km to North Norway) lasted for about 4 days in autumn and 3 days in spring. Later arrival resulted in later nest initiation, implying a carry-over effect of winter conditions on subsequent breeding. Birds that migrated to Norway departed later from Svalbard in autumn and consequently spent less time in the wintering area than individuals that migrated to Iceland. As just two countries, Iceland and Norway, appear to host all common eiders from Svalbard during the winter, the new information provided by this study on the core areas and timing of migration should provide the impetus for improved bilateral conservation management of this important Arctic breeding population of common eiders.