All three countries use the Roman Iron Age for the time period up to 400 AD. Then there are differences:
Norway: The Late Iron Age: The Migration Period 400-570/600, the Merovingian Period 570/600-800 and the Viking Age 800-1050.
Sweden: The Late Iron Age (400-1050) includes the Migration Period 400-550, The Vendel period 550-750 and the Viking Age 750-1050.
Denmark: The Germanic Iron Age 400 AD – 750/800 AD. This period is divided into the ’Early Germanic Iron Age’ or the Migration Period 400 – 550, The Later Germanic Iron Age’ 550-750. Then follows the Viking Age 750/800-1050.