In 2026, the best time to buy your Interrail Pass is roughly 1 to 3 months before your trip, but there are a few nuances to consider. You can purchase a pass up to 11 months in advance, which is useful if you catch one of Interrail's frequent "Flash Sales" (often in March or December) where prices are slashed by 10% to 15%. However, the most important factor isn't the pass itself, but the seat reservations. For high-speed trains like the Eurostar, TGV, or Italian Frecciarossa, and all night trains, a seat reservation is mandatory and can sell out months in advance during the peak summer season (June–August). Since you need your Pass Number to book these reservations in 2026, you should secure your pass as soon as your travel dates are firm. If you are traveling in the "off-season" or plan to stick primarily to regional trains (which don't require reservations), you can wait until a few days before departure. Most 2026 travelers opt for the Mobile Pass, which allows you to buy the pass instantly and "activate" it on your phone the moment you board your first train.