This year, hotels in Florence, Italy, in September were charging close to summer highs. I was priced out of Key West, Fla., in November, a historically slow month. Considering the eco-friendly resort Playa Viva near Zihuatanejo, Mexico, for the first week of December — long a bargain time to travel — I could find only one night available at rates below $500.

What, I wondered, happened to the off-season?

“September is the new August,” said Jack Ezon, the founder of Embark Beyond, a high-end travel agency based in New York City, explaining that the frenzy for European travel stretched the calendar. Nearly a third of his clients who regularly travel to the Mediterranean in July and August rescheduled for June, September or October.

“People are making choices to avoid the crowds and the heat,” said Virgi Schiffino Kennedy, the founder of Lux Voyage, a travel agency based in Philadelphia.

“I’m seeing summer rates creeping into shoulder season,” she added, noting that destinations like Santorini and Mykonos in Greece, which peak in July and August, “are now impossible to book in September.”

School calendars still largely dictate the biggest peaks in travel annually, but the dips are not as dramatic — in numbers and in rates.

“I think we’re at the beginning of a change,” said Henry Harteveldt, a travel industry analyst who runs the firm Atmosphere Research Group based in San Francisco, crediting flexible work schedules for the trend. “Summer will always be peak season, but I think we’ll see more off-peak travel in fall, winter and spring so those valleys may be less deep.”

Travel is most certainly back — the World Travel & Tourism Council said the industry will recover 95 percent of 2019 activity this year — but it’s not a replica of prepandemic patterns.

Compared to 2019, global leisure stays were up 12 percent in spring 2023 at more than 230 Sofitel and MGallery hotels. Fall 2022 bookings were up 7 percent for leisure guests compared to the same period prepandemic.

“Booking shoulder season was once travel’s best-kept secret, but more people are catching on to the trend,” said Matt Berna, the president for the Americas of Intrepid Travel, a global tour company. He said fall and spring bookings this year have grown by 56 and 70 percent, respectively, compared to prepandemic business, inspiring the company to increase its departures to meet the demand.

The river cruise line AmaWaterways has done the same, adding new itineraries for November and February.

G Adventures, which offers small-group trips, said bookings by Americans are up 40 percent this year over 2019. When summer trips in Italy sell out, travelers are bound to look deeper into the calendar, said Steve Lima, the vice president of growth for the U.S. and Latin America for G Adventures.

“It’s like Disney’s always busy and there’s no good time, so you just go,” Mr. Lima said.

Katie Parla, a Rome-based cookbook author who guides private food tours, described a pig-in-the-pipeline scenario where travelers who booked a tour for their 35th wedding anniversary weren’t able to take it until their 37th because of travel restrictions and complications over the past few years.

“The high season used to be Easter to October, but this year Rome started to be slammed a full month earlier and my calendar is nearly full through the end of December already, which is very rare,” Ms. Parla said.

Under a canopy of brightly colored fall leaves in orange and yellow, a family group is scene in front of a large R.V. A man hands a woman firewood while children sit near a dog and another man tends a firepit in the background.

Kampgrounds of America recently found 67 percent of campers had changed their travel plans this year because of the weather.Credit...Kampgrounds of America

The seasonal switch isn’t just a European phenomenon. Apple Leisure Group, which offers value-priced vacation packages in Mexico and the Caribbean, has seen bookings more evenly distributed throughout the year over the past three years. As a result, its prices are more consistent year-round.

In an August report, Kampgrounds of America found 67 percent of campers had changed their travel plans this year because of the weather. Nearly 64 percent of campers who delayed trips planned to take them after Labor Day. The R.V. rental platform RVSharesaid shoulder season reservations have grown twice as fast as those in their core summer season, which it attributes to flexible work policies and efforts to avoid extreme heat.

Claire Ramsdell, 31, who works nomadically in customer service for an outdoor company and blogs about hiking, spent the summer in Bozeman, Mont., but found it too hot to work from her vehicle, forcing her to rent high-price accommodations with roommates and poor Wi-Fi.

“I’m not sure why I tried to branch out and do such a popular and expensive destination this summer,” she wrote in an email from Colorado where she plans to hike this fall. “I should go back to off-season travel and less-crowded places.”

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