For most airports, you must be checked in at least 30 minutes before your scheduled departure time (airports requiring additional time are listed below, Go to footer note). Additionally, you're required to be at the gate and ready to board 15 minutes before scheduled departure.

The deadline for checking in for a flight varies depending on whether the flight is domestic or international and the specific policy of the airline. For domestic flights within the U.S., the most common deadline is 45 minutes before the scheduled departure time if you have bags to check, and 30 minutes if you are traveling only with carry-on luggage. For international flights, the requirement is much stricter, typically requiring you to check in at least 60 to 90 minutes before departure to allow for passport verification and more complex security protocols. It is important to note that "check-in" is different from the "boarding" deadline; most airlines close the aircraft doors 15 to 20 minutes before takeoff. If you arrive at the airport after the check-in window has closed, the airline's computer system will often lock your record, and agents may not be able to issue a boarding pass even if the plane is still at the gate. To be safe, travel experts recommend arriving at the airport at least two hours before domestic flights and three hours before international ones to account for unpredictable security lines and ensure you meet these non-negotiable deadlines.