Reservations for Sweden are best booked via SJ but you have to indicate you have an Interrail pass, otherwise the website will of course show the normal fares.

You'll need a pass cover number to enter on the SJ website.

USe FAQ on sj.se: there it will tell how to do it with pass-it will go via the way of PRIO fixed customer card-you really have to know-and probably try it out once-how it works

For the superfast X2000 trains the price is more near to 10€-most other trains are optional REServ.

It's only on the SJ snabbtåg (high speed train) and the night trains where you need a reservation.

On the other trains that are included in Interrail/Eurail you don't need a reservation. However, if you are travelling a longer distance on a busy day you might want to make a reservation anyway.

If the planner says that the reservation fee is €3 then the reservation is not mandatory. There is an error in the planner.