I don't see any results when I try Milano Centrale to Interlaken Ost on Rail Europe. Please mention the departure time you're trying to book.
Please also take into account:
- You don't have a 5-trip pass, but rather a pass with 5 travel days. You can use as many trains as you like on each of those days.
- The annual timetable change is on 14/12 this year, and not all timetables have been published yet. Also, not all trains are bookable yet, e.g. the earlier trains on 2/1/2026 Milan-Zurich, e.g. at 8:10 and 9:10.
- The normal route from Milan to Interlaken is via Spiez. Via Zurich is a big detour. No timetables have been published yet for the route via Spiez.
- Reservations for Swiss domestic trains are a waste of money, in the trains where they're at all possible.
- Reservations via Eurail are best avoided, since they add a €2 booking fee per person and train. Check this page for the best places to book pass reservations. raileurope.com is a good place to book Milan to Switzerland. Reservations should be €13 per person for these trains. On Rail Europe, always set currency to euro to avoid their 5% mark-up for other currencies.
Honestly, I wouldn't book any reservation yet before it's clear what's happening on the route via Spiez.
Alternatively, you can also travel reservation-free and (if you want) via the Gotthard mountain route, where you'll have much more beautiful views than in the long Gotthard tunnel. Or travel via Luzern-Interlaken.