The direct day trains Copenhagen-Stockholm have mandatory reservations. You can book them on sj.se. If you don't have a reservation, you'll get a fine and/or you'll have to leave the train.
You can travel from Stockholm to Copenhagen with reservation free regional trains. There are several options. You will have to change trains several times and it will take between 9 and 12 hours. There are many more options than those shown in the Railplanner. There are reservation free trains from Stockholm to Gothenburg which incorrectly are marked as âmandatory reservationâ in the Railplanner. From Gothenburg there are reservation free ĂresundstĂ„g to Copenhagen.
During the summer all trains going south from Gothenburg will start in Mölndal due to track works so you need to take public transportation from Gothenburg main station to Mölndal if you choose to travel this way,
When do you plan to travel?