How late can I be to an airport and still board?

Thanks to being a loyal TSA PreCheck and Clear member, I usually experience little to no wait time at all to go through the U.S. Transportation and Security Administration line at airports where Clear and TSA PreCheck are available.

Even when I have this peace of mind, derived from flying out of airports and with airlines offering both expedited security programs, I still tend to arrive at the airport earlier than necessary just in case something unexpected occurs.

Even for travelers like me though, sometimes unusual circumstances prevail, resulting in a later-than-planned arrival at the airport, which recently happened to me.

An unexpected, nearly hourlong Uber ride to Los Angeles International Airport (LAX) had me panicking ever so slightly about navigating security at LAX's Terminal B without TSA PreCheck or Clear, since the airline I flew does not participate and Clear was not available in the terminal.

As I waited approximately 45 minutes to get through security, I wondered how late I could arrive at the gate without missing my plane.

Although some airlines provide a bit more leniency for travelers than others, most airlines have standard check-in time requirements that vary depending on whether you are flying on a domestic or international route.

Although this is the absolute latest time you can check in at the airport and still receive a boarding pass, you'll also need to consider how late you can arrive at your gate.

This guide details check-in and gate arrival requirements for major carriers.

Alaska Airlines

Regardless of whether you are checking a bag, all Alaska Airlines passengers must check in for their flight no less than 40 minutes before domestic flights and one hour before international flights.

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To ensure your bags are turned over in time, Alaska advises travelers checking bags to be at the airport even earlier to be in the bag drop line before the aforementioned cutoff time.

After checking in, Alaska flyers should be at the gate, ready to board, no later than 30 minutes before their flight.

"Being late may cause the cancellation of your reserved seats and/or your entire reservation," says Alaska.

American Airlines

AA travelers can expect AA flights to board within 30-50 minutes before scheduled departure, though the exact boarding time depends on your destination and aircraft.

For American Airlines flights, boarding ends 15 minutes before departure, regardless of the destination. This 15-minute gate closure time is standard for most domestic carriers in this guide.

"If you're not on board, we may reassign your seat to another passenger," per American. "You will not be allowed to board once the doors close."

To check in and also check bags, you must do so at least 45 minutes ahead of your flight for flights within the U.S., and within an hour for international flights.

Delta Air Lines

Like Alaska, Delta passengers must check in at least a half hour before their flight and be at the gate and ready to board at least 15 minutes before scheduled departure.

If you are flying Delta internationally, the minimum check-in time is one hour before departure, while Delta says you must be at your gate 45 minutes ahead of your flight.

JetBlue

In perhaps the most generous international check-in policy of all the carriers mentioned in this guide, JetBlue allows passengers on international flights to arrive at the gate up to 20 minutes before departure, while following the somewhat standard 15-minute window for boarding domestic flights.

Customers traveling on international flights, though, must check in at the airport no later than 60 minutes before departure, in which case the 20-minute window before boarding would only apply if you experienced a delay between checking in and arriving at the gate. There's also a 60-minute window for international passengers checking bags to check in at the airport. Otherwise, all other JetBlue bags must be checked at the airport 40 minutes before departure.

Related: What to do if a boarding pass isn't marked TSA PreCheck

Southwest

Southwest takes the cake among domestic carriers for being the most generous with its check-in policy. It allows customers to board all the way up to 10 minutes before their flight's scheduled departure.

Even so, the Dallas-based airline encourages all passengers to plan to arrive in the gate area no later than 30 minutes before departure.

United Airlines

Of the Big Three —American, Delta and United — United has the most varied check-in policies for its travelers based on the route, as follows:

• For most United- and United Express-operated domestic flights, travelers not checking bags must check in for their flight at least 30 minutes before departure.
• For most United- and United Express-operated domestic flights, travelers with checked luggage need to check in at least 45 minutes before departure.
• For most United- and United Express-operated international flights, travelers must check in at least an hour before departure, regardless of whether they are checking luggage.

When it comes to being at the gate, all customers must be on board the aircraft 15 minutes before the scheduled departure time for flights within the U.S.

"We recommend being at the boarding gate at least 15 minutes before departure to ensure that you're on the aircraft before the doors are closed," says United. "For international flights, we encourage you to be at the gate no later than 30 minutes before your scheduled departure."

Bottom line

In addition to the above policies set forth by airlines, also know that airports set requirements for travelers regarding the latest time you can arrive at the airport without risking missing your flight.

Most U.S. airports require passengers to check in for their flights at least 30 minutes before their scheduled departure time, though some require additional time, regardless of whether you are checking a bag.

For example, all passengers flying out of Toronto Pearson Airport (YYZ) must check in 90 minutes ahead of their flight, while those departing from Amsterdam Airport Schiphol (AMS) must check in within 75 minutes. If you have questions about a specific airport, we recommend contacting the airport directly to verify its minimum check-in time.

If you are checking a bag and flying within the U.S., the majority of airports require you to check in 40-45 minutes before your flight, though John F. Kennedy International Airport (JFK) is a notable exception to this, requiring passengers to do so 60 minutes before. If you are like me and refuse to check a bag, plan on being able to arrive at the airport within 30-45 minutes for domestic flights and at least one hour when traveling internationally.

If you find yourself in a long security line, at risk of missing your flight, kindly ask a TSA agent or the relevant airport security employee if you might be able to skip ahead in line. I have seen people do this before and the TSA agent usually helps these travelers in my experience.

Despite your best efforts, sometimes travel days do not go according to plan. Be sure to review the minimum requirements for the latest time you can check in for your flight and arrive at your gate, set by the carriers and some airports.

Read more: 7 ways to get free or discounted TSA PreCheck, Global Entry and Clear