As a general rule, any train shown in its database can be used with an Interrail pass, although supplements or special fares must be paid on some. It will also show which trains have compulsory reservations.

While an Interrail pass covers the base fare of your journey, you often have to pay extra for seat reservations, which can feel like an "extra" charge for many travelers. In most of Western and Central Europe, high-speed trains (like the TGV in France, Eurostar, or AVE in Spain), international routes, and overnight sleeper trains require a mandatory reservation fee that is not included in the price of your pass. These fees can range from a few euros for a standard regional seat to over 30 euros for premium high-speed links. However, in countries like Germany, Austria, and Switzerland, many regional and even long-distance trains do not require reservations, allowing you to simply hop on and off with just your pass. To travel without paying anything extra, you can often choose slower, regional routes that don't require booking. So, while the "ticket" is paid for by the pass, the "right to a specific seat" on a popular train often comes with an additional cost that you must budget for when planning your European rail adventure.