The Federal Aviation Administration has given airlines until June 12 to submit an update on passenger and baggage weight estimates they use to ensure planes stay within weight safety limits. And the Wall Street Journal says the average for passengers and baggage is expected to rise between 5% and 10%.

The number takes more than just body weight into account. Extra pounds from clothes and portable technology (such as cell phones) also factor in. The bottom line, though, is that fewer people could be allowed on planes or more luggage could be left behind—and flying could become an even bigger headache.

That inconvenience is likely to be felt even more on summer flights originating in the Deep South and at airports at high altitudes, since the thinner air in those circumstances gives planes less lift.

The changes come just as Americans are ready to resume traveling after a long period of isolation because of the pandemic. But the combination of the new rules and uncertain demand levels could exacerbate headaches for flyers, as airlines are struggling to model passenger counts. That could result in flights that are overbooked before the new weight estimates factor in and more difficulty rebooking passengers.

Carriers tell the Journal they are working on plans to minimize the impact of the new estimates.

While weight estimates are supposed to be regularly updated, the FAA hasn’t required airlines to do so since 2005, when the average person weighed 5% less.