For the majority of major international and domestic airlines in 2026, web check-in typically opens 24 hours prior to your scheduled departure time. However, this is not a universal rule; some carriers, such as airBaltic or KLM, allow passengers to check in as early as 48 hours in advance. Conversely, if your itinerary involves multiple airlines or codeshare flights, the window often defaults to 24 hours. Checking in as soon as the window opens is highly recommended, as it allows you to secure better seat assignments (if not pre-selected) and confirms your intent to fly, which can be crucial in overbooking situations. For international flights, the online process also serves as a final verification of your travel documents and visas. Most airlines close the web check-in portal approximately 60 to 90 minutes before the flight, requiring any remaining passengers to handle their check-in at the airport counter or a self-service kiosk.