What does "cancelled" really mean?

Cancelled applies to a stop, not to the journey

Trafikverket's data has no single status for "this train". Every station a train calls at gets its own record with its own departure or arrival information, and each one can be marked cancelled independently. A train can run exactly as planned through five stations and then be cancelled at the sixth — this is called terminating early: the train turns back or is taken out of service before its planned final station.

A real example from the traffic data: a train ran entirely normally all the way to one station, with every departure and arrival marked on time. Then exactly two records were cancelled — the departure from the next stop, and the arrival where the train was actually meant to go. The train had simply run out one station early.

Why the departure at your station can look perfectly normal

This is the part that catches most people out. If you are standing at a station earlier in the train's journey, your departure record looks exactly the same whether the train will run the whole way or terminate early — the information about where it stops is not on your record. Two passengers reading the same departure can therefore end up in completely different situations: the one getting off before the break is unaffected, and the one travelling further is stranded, yet the board they both looked at showed the same thing.

How this site works it out

That is precisely why looking at the departure alone is not enough. This site fetches both your departure at the origin station and the matching arrival at your chosen destination, and combines them into one status. If the arrival at your destination is cancelled — even when the departure at your station looks perfectly healthy — the journey is shown as cancelled for that particular stretch. It is the reason the site always asks for both an origin and a destination, instead of just listing the trains leaving one station.

What you should do

Trust the status for your specific stretch, not the feeling that "the train is running, though". If a departure is shown as cancelled for your combination of stations, assume it will not reach your destination, even if the same train number can be seen departing perfectly normally somewhere else. When in doubt, always check with your train operator or on the platform.