Whether you can check into a flight 48 hours before departure depends entirely on the airline you are flying with. While the industry standard for most major carriers (like Delta, United, and British Airways) is 24 hours before the scheduled departure time, some airlines—particularly low-cost and international carriers—offer a much wider check-in window. For example, Lufthansa and Swiss typically allow check-in starting 23 hours before, whereas Ryanair allows guests who have purchased a specific seat to check in up to 60 days in advance. Other airlines, like Air France and KLM, open their check-in window at the 30-hour mark. If you have a connecting flight, you are often checked in for the second leg at the same time as the first, which can sometimes be more than 48 hours before the final arrival. It is essential to check your airline's specific policy via their mobile app, as checking in as early as possible is the best way to secure your preferred seat and avoid being "bumped" in the event of an overbooked flight. If the window hasn't opened yet, the app will usually display a countdown timer indicating exactly when you can begin the process.