You can check in for a United Airlines flight starting 24 hours before the scheduled departure time through the official United website, mobile app, or airport kiosk. Online check-in is available for both domestic and international flights and remains open until 45 minutes before domestic departures and 60 minutes before international flights. This check-in process allows travelers to select or change seats, add checked baggage, and receive digital boarding passes, which can be saved to a mobile device or printed at home. For those flying with carry-on bags only, completing online check-in saves time at the airport by allowing you to proceed directly to security. United Airlines also offers airport check-in at self-service kiosks and ticket counters. Kiosks typically open about 3 hours before departure and close around 30 to 60 minutes before the flight, depending on the destination. Curbside check-in is available at select airports, opening approximately 4 hours before departure and closing 40 to 45 minutes before takeoff. Passengers who need special assistance, are traveling with pets, infants, or unaccompanied minors, or have international travel with document checks should check in at the airport counter. United recommends arriving at the airport at least 2 hours before a domestic flight and 3 hours before an international flight to allow time for check-in, baggage drop, security screening, and boarding. Boarding gates close 15 minutes before domestic departures and 30 minutes before international flights, so completing check-in early helps ensure you don’t miss your flight. Using the online check-in option at the 24-hour mark is a good strategy for selecting better seats and reviewing your itinerary. The system is easy to use and offers prompts for any additional services needed. Many travelers find that checking in early reduces airport stress and helps them stay organized on the day of travel. In summary, United Airlines allows check-in 24 hours before your flight, with cut-off times of 45 minutes before domestic and 60 minutes before international departures. Airport kiosks and counters typically open 3 to 4 hours before the flight, providing multiple options to complete the check-in process based on your needs. For a smooth travel experience, it’s important to follow United’s check-in deadlines, arrive early, and use online tools when possible to make your journey more efficient and comfortable.