How much time do you really need for a layover?

Theoretically, when you book air travel online, any available tickets that include layovers should allow you enough time to make your connecting flight. In reality, it’s not quite that simple. The itinerary may technically meet an airport or airline’s required minimum connection time, but the layover could still prove to be too close for comfort when you’re actually en route. “At the end of the day, it’s up to you to do the research to ensure you have sufficient time to make your connection,” said Daniel Gillaspia, CEO and founder of travel rewards blog Upon Arriving. “Just because an [online travel agency] is offering you an itinerary...doesn’t mean it will work for you on your travel day.” As for how much time you do need to allow on a layover, that answer depends on the specifics of your journey:

Traveling domestically

“For the most part, an airline isn’t going to give you less than an hour [or so for a layover] because it’s a miss for them if you miss [your next flight] too,” said Kristin Addis, CEO of Be My Travel Muse. “If it’s domestic — especially if there [are] going to be multiple flights to the same destination — [if] my incoming flight is delayed [and] they can just easily bump me to another one, then I don’t worry too much. ...Maybe that’s playing with fire a bit, but I don’t love long layovers, so it’s always trying to strike a balance between not being at the airport forever and not missing your flights.”

If you’re also comfortable with a tight layover, do the research in advance to make sure there are indeed additional flights to your destination scheduled in case you do miss the second leg of your trip. Otherwise, build in a bit more time. Gillaspia recommends 60 to 90 minutes for domestic layovers; if you like to play it safe, aim for the 90-minute options.

Traveling internationally

“If you are arriving at a large airport from an international flight, you should give yourself a minimum of three hours between flights to allow yourself to clear customs [and] passport control, re-position at the appropriate terminal and re-check bags, as you must claim bags and re-check them at the first port of entry,” said Stephon Owens, CEO of home exchange platform Vezpuchi. That’s also commonly the case, noted Michelle Anderson, supplier marketing manager at Hotwire, if you’re flying from the U.S. and have a layover in a foreign country before continuing on to a different destination. Not only may you have to pick up your checked bags and wait in lines for customs and immigration checkpoints, but you also may be subject to bag searches which can add even more time.

Even if the airport you’re connecting in isn’t a huge one, Gillaspia recommends giving yourself two hours for an international layover. “On bad days, you could get stuck waiting 45 minutes to an hour [to get] through immigration,” he said. “If you had a delay to go along with that, you could be cutting it very close in many cases.” He noted you can find data on customs and immigration wait times on the U.S. Customs and Border Protection website, which could help you plan your itinerary.

When facing likely delays

“It’s most important to remember that you have no control over delayed flights,” Gillaspia said. “You can plan your way through the airport terminals by the minute, but that plan will be worthless if you end up having to deal with an unexpected delay. So always plan for delayed flights.” That’s especially important if you’re flying to or from a destination that’s likely to have inclement weather, or connecting in an airport that’s prone to delays. “This would include cities in the Northeast and Midwest during winter; and the NYC area airports in general, since NYC is prone to operational delays because of congested airspace,” Owens said. With a bit of searching, you can find information on the most delayed airports in the world and in the United States; and you can even check out the on-time history of the specific flights you’re booking through sites like FlightAware and the U.S. Department of Transportation.

In general, Owens recommends allowing yourself at least two hours between flights if you’re traveling from or connecting in a city that’s prone to delays and your layover is in a large airport; and one hour if the layover is in a small airport.

When connecting in big or complicated airports

In fact, the airport you’ll be passing through is an important factor in determining the appropriate layover time. Start by looking up the size of the airport: If it’s pretty compact, you don’t need as much time. But if it’s sprawling, even moving between two gates in one terminal could be a hike. “I’ve had to run across Amsterdam airport before because [of] an hour-long layover,” Addis said. “Even if there’s a 10- or 20-minute delay [with your incoming flight], if you only have an hour and it’s a big airport, you can really end up having a bit of stress there.”

That said, small airports don’t guarantee easy connections either. “Each airport is different but it’s important to keep in mind that even small airports can be complicated and have shuttles between terminals,” Anderson said. “My advice is that if your connection is tight and you are unfamiliar with the airport, do some research on the layout of the airport prior to departure.” On any given airport’s website, you should be able to find information about not only the layout and the terminals you’ll be flying into and out of, but also protocol specific to that airport. As Anderson said, “Some airports require you to go through security, baggage claim or passport control again before boarding a connection, causing delays.” If that’s going to be the case with your trip, consider adding an extra 30 minutes or even an hour to allow yourself plenty of time for lines, questioning and the like.

When checking bags

In most cases — especially if you’re flying one airline on one ticket — any bags you check will be checked all the way through to your destination. But, again, depending on the airport, you might have to pick them up and re-check them during your layover — so you’ll definitely want to pad your connection time if that’s the case. And even if it’s not, keep in mind that, just as you have to get from airplane A to airplane B, so does your bag. If the connection is extremely tight, there’s always the possibility (even if rare) that the airport crews won’t have enough time to unload, transport and re-load your luggage before your second flight takes off. “A couple times my bag hasn’t made it because my incoming flight was delayed, and I just barely made [the second one],” Addis said. “If you really want to minimize the possibility of that, a couple hours, minimum, is good.”

Flying with multiple airlines

If you can, your best bet is to book your entire journey on a single ticket with a single airline. In that case, the airline should be able to fairly easily re-book you on the next available flight if you miss your connection. But, “if you booked them separately and you encounter a delay on your first leg [and] miss that second flight...you’re probably just going to eat that ticket,” Addis said. That said, if you do book a multi-airline trip through an online travel agency, that company may provide the necessary re-booking assistance — but be sure to check the terms and conditions before buying your ticket.

Rebooking aside, flying on two different airlines could mean a more complicated layover. “A lot of times, different airlines will serve different terminals and these may not be connected airside,” Gillaspia said. “In those cases, you’ll probably need to add extra time. The airport’s website should tell you which airlines serve which terminals so you should have an idea of that before you book.”

Owens said he gives himself at least four hours for a connection if he’s traveling abroad on separate itineraries within the same day; but, again, it’s important to consider the many various circumstances of your trip to determine what makes sense for you.

Remember, too, that you don’t have to figure this out on your own. “If you’re considering a flight with a connection time that looks tight, call the airline directly to discuss your options,” Anderson said. “While traveling, flight attendants are also very knowledgeable and excellent resources who might be able to tell you more about the terminal you’re flying into. If you are running low on time, it’s worth asking your fellow passengers to let you de-plane sooner — they often help you out so you don’t miss your flight.”

You can also communicate the urgency to airport and airline employees and security agents, as well as other travelers standing in line, all of whom may help you get to the front and get on your plane.

Ultimately, “there’s no perfect equation,” Anderson said. “Sometimes it takes 10 minutes to connect, and sometimes it takes an hour. Use your judgment and don’t put yourself in a position where you feel you are cutting it too close.” And if the thought of a close connection or a potential missed flight sends your stress levels through the roof, consider embracing a long layover instead — you might even get a bonus adventure out of it.