Domestic airfare up 40% from start of the year: Hopper

Domestic airfare is up 40% from the start of the year and is expected to climb another 10% next month, according to online booking platform Hopper.

Last month, average airfare in the U.S. went up 5.2%, the third largest one-month jump since 1999, according to Scott Keyes, founder of Scott's Cheap Flights.

Hopper said the cost of a domestic round trip is averaging $330 -- 7% above 2019 prices. For international trips, the average round trip cost is $810, up 25% from the start of the year.

Pent-up demand and rising prices of jet fuel are driving the change.

"A tremendous amount of demand [is] from travelers who have not been able to travel the last two spring and summer seasons," Haley Berg, economist at Hopper, said in an interview with ABC News. "And the second factor is jet fuel. Jet fuel prices are also up 40% since the beginning of the year and up 75% since this time last year. Demand and higher jet fuel prices together are really driving overall domestic airfare up."

But it's not all bad news. Keyes said average airfare doesn't tell the whole story.

"A lot of folks see that headlines about airfares going up, and they're worried that they're not going to get any cheap flights anymore. And I actually think that's the that's the wrong way to look at things," Keyes said in an interview with ABC News.

In the past two weeks, Keyes has found deals like $215 round trip to Hawaii, $395 round trip to Milan and $579 round trip to Australia.

"While it's creeping back up, it's important to remember we are still living in the golden age of cheap flights. Tickets are significantly cheaper than they used to be even a decade or two ago," Keyes said.

To get those cheap fares, Keyes said it's important to book one to three months in advance for domestic trips and two to eight months ahead for international trips.