For a domestic connection, plan on at least 60 to 90 minutes between flights. For an international connection, give yourself 2 to 3 hours, since you may have to clear customs and immigration. Airlines set their own official minimums per airport, but those are the bare floor, not a comfortable buffer.
Here is the honest version: the number the airline uses to sell you a tight connection is not the number you actually want. Airlines set a minimum connection time (MCT) for every airport, and it is the smallest legal gap they will let you book. It assumes everything goes right. Real travel rarely does, so smart planning means giving yourself more room than the minimum.
MCT is a published standard, agreed between airport and airline committees and listed by IATA, that says how quickly a person can realistically get from one gate to the next at a given airport. It factors in things like walking distance, whether you change terminals, and whether bags move automatically. If a connection meets the MCT, the airline's booking system will sell it. If it does not, you cannot book it as one trip. The key thing to remember: MCT is the floor, not a recommendation.
How much time you need depends heavily on the type of connection:
The international arrival step is the one that surprises people. Even with a bag checked to your final city, entering a new country often means grabbing it for customs, then handing it back. That is real time on the clock.
This is where being on one ticket matters. If both flights are on a single reservation and an airline delay makes you miss your connection, the airline will normally rebook you on the next available flight at no extra charge under its contract of carriage. If it cannot get you there and you decline the alternative it offers, US Department of Transportation rules require the airline to refund the unused part of your fare. If you built the connection yourself on two separate tickets, that risk is on you, and a missed leg can mean buying a new one. Europe works similarly on rebooking, and EU air passenger rules can also add cash compensation for long delays on covered flights.
Book at or above the MCT, then add a real buffer: aim for at least 60 to 90 minutes domestic and 2 to 3 hours international, and stretch that if you are connecting through a huge hub, traveling in winter, or cannot afford to miss the second flight. Use the FlightBeat calculator to see your first leg's true flight time and landing time, so you can judge whether that layover is comfortable or a gamble before you buy.
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