Nyköping has good connections to Stockholm by both train and bus. The town sits on the main southern rail line, with regular services to Stockholm Central taking around 90 minutes. Flixbus and several Swedish regional operators serve the route as well.
Stockholm Skavsta Airport is 5 kilometres northwest of the town centre. It is marketed as a Stockholm airport and used mainly by Ryanair. A dedicated airport coach runs between Skavsta and Stockholm city centre in about 80 minutes; a separate local bus links the airport to Nyköping town. If your flight lands at Skavsta and you want a night in a real Swedish town before heading to Stockholm, Nyköping is the obvious and often overlooked choice.
By car, Nyköping is about 100 kilometres southwest of Stockholm via the E4 motorway.