Summer still isn't over, but Expedia.com flight data released today shows that getting an early start on planning holiday travel can yield significant savings. Thanksgiving and Christmas are two of the busiest travel periods each year, and in 2016, Expedia data revealed more than 85 percent of holiday travelers missed out on locking in the lowest fares.

"Timing is a big factor in getting a good deal on airfare," says Sarah Gavin, vice president of global communications for Expedia. "People typically know pretty far in advance whether they're going to travel for the holidays, so it's a good idea to keep an eye on prices months out. Even with holiday travel, a general rule of thumb applies: If you find a fare that seems like a good deal, buy it."

When to book for Thanksgiving

According to Expedia flight data for 2016, the sweet spot for booking Thanksgiving travel is 61-90 days out. Travelers who booked during that timeframe saw savings of up to 10 percent, while those that waited until the last minute, zero to six days out, paid more than 20 percent above the average ticket price. For 2017, the optimal window to book and save begins today and runs through September 23.

When to book for Christmas

For Christmas, the cheapest time to book travel is 14-20 days out, where travelers saw savings of around five percent in 2016. Like Thanksgiving, last minute bookers are in danger of paying a premium, more than 15 percent above average ticket prices.

Where to go this fall

As the summer comes to an end, many global destinations are heating up in terms of savings. Expedia flight data shows several destinations across Europe and Asia that are cheaper for U.S. travelers in the fall. During the months of September – November, these are the destinations where fall means savings: