Holiday travelers may need to brace themselves for the millions of people taking to the skies for the holidays — and depending on your location, some airport crowds and difficulties may be worse than others.

A total of 47.5 million people are expected to fly all over the world on U.S. airlines during the Christmas and New Year’s holiday period this year, and passenger rights company Airhelp has broken down the numbers and trends at popular airports.

Passengers flying in and out of Chicago’s O’Hare International Airport should allot extra time in their trip as the Midwest transit hub came in as having the most travel disruptions over Christmas last year.

Analyzing flights from last year’s peak holiday travel period, Airhelp found that O’Hare (the busiest airport in the U.S) came in as having the most travel disruptions over Christmas, while the second most hectic hub was Atlanta’s Hartsfield-Jackson International Airport followed by Los Angeles International Airport.

“While there is no way to avoid delays and disruptions, travelers can prepare for common issues such as traffic delays, long lines, and overcrowding at the airport,” Johnny Quach, AirHelp’s chief product officer, told Travel + Leisure. “A high volume of travelers means that delays, overbookings, and cancellations are highly likely. Weather delays will most likely increase as well, as many regions of the United States are impacted by colder weather.”

When it comes to the routes most plagued with issues, the one travelers had to watch out for last year was between San Francisco’s International Airport and LAX, according to the report. These short California flights — both ways — were the two most disrupted in the whole country during the Christmas travel period last year.

Travelers check-in for flights in the airport terminal at Ronald Reagan Washington National Airport
Credit: SAUL LOEB/Getty Images

And while flight issues are inevitable, AirHelp estimated that 81 percent of American travelers don’t know their rights when they are delayed, bumped, or their flight is canceled. If you’re traveling to or from the European Union on an EU airline, for example, Quach said, you are entitled to up to $700 for flight delays of more than three hours.

“If you are denied boarding or experience a cancellation, it is important to keep all of your travel documents, find out why the disruption occurred, and request compensation for the disruption,” Quach said. “If you’re flying within the U.S., while you won’t be eligible for compensation after a lengthy delay, if you are bumped from your flight or denied boarding because the airline oversold seats, you do have rights you should know about and be prepared to exercise.”

Quach noted that the earlier in the day you book your flight, the better chance you have of it taking off without a hitch. Pro tip: The best time of the day to fly may require an early wakeup call as it was found to be between 6 a.m. and 11:59 a.m.

“If you have a later flight booked, make sure you know your rights in case you experience overbookings or delays,” he added. “Because delays seem inevitable, it is important to read up on your rights and be prepared.”