The "+1” just means that you arrive the next day. It doesn't say anything about the number of travel days you need.

If you want to check travel times, please do not use the rail planner app or the Interrail website. They don't receive enough updates to be reliable. Instead, use the national websites or apps; for international travel, the DB website or DB Navigator app is a good choice.

Thanks, but how do I know how many travel days am I using during the entire trip?

You just count them after you've looked up the timetables. You can board as many trains as you want on a travel day and a travel day runs from 0:00 until 23:59 CET.

I see the following routes:

• Barcelona-Paris. Easily doable in 1 day, two daily TGV's take 6h40 (require expensive reservation, €35).
• Paris-Amsterdam: Also easily doable, numerous Thalys trains take 3h30 (also require expensive reservation, €30. These are limitedly available, check on https://www.b-europe.com/NL/Kopen/Pass if they are still available).
• Amsterdam-Copenhagen: tight in one day, but possible. About 11-12 hrs, reservations for the Hamburg-Copenhagen train are compulsory in Summer.
• Copenhagen-Vienna: Possible with day trains, though it might be a bit tight: Easily possible with just one travel day if you connect onto the NightJet sleeper in Hamburg. Sleeper spaces sell out, so be sure to check whether they are still available. You only need to use a travel day on the day of departure (if it leaves before midnight CET), but you can remain on the train until Vienna.
• Vienna-Budapest: Easy, many trains a day
• Budapest-Split: Not sure whether this is possible in 1 day, it seems you might need to split in Zagreb. There might be night trains running there in Summer but I’m not an expert on that area.
• Split-Ljubljana: Seems to be possible in a day, but it's a long trip. I have not travelled in Croatia so maybe others can help.
• Ljubljana-Milan: Possible in a day, switch in Villa Opicina, Trieste and Venice Mestre. According to DB only with a early morning (05:47) departure if you want to avoid having to cross the border walking at Nova Gorica-Gorizia (4km), or at 07:26 via Villach (Austria). So you might possibly want to split this up too.

Based on this it looks like a 10-day in 2 months pass should be enough. There's 8 legs of which for one you’ll likely need 2 travel days (Budapest-Split). If you decide to split up other long travel days you might need more travel days, or you can use advance-purchase full price tickets instead of some travel days (eg: Vienna-Budapest tickets can be bought for less than €20 when booking in advance, and Thalys Paris-Amsterdam also can cost just €35 booked well in advance, which is nearly as much as the passholder reservation of €30).

There should be a direct night train Budapest - Split in summer but I only expect information about that a few weeks before it starts running.

Thank you very much! Another question: How do you book a night train? Is it any different than normal or day trains?

Read the community’s guide on getting reservations here:

You’ll need to look into the Nightjet section for the Hamburg-Vienna sleeper.