Congratulations, you survived another year of holiday travel. However, before you settle into your leather sectional and refuse to lift your "Complete Purchase" finger for another 316 days, you might want to rethink your non-strategy strategy.

"This is a great time of the year to start planning a trip," said Patrick Surry, chief data scientist at Hopper, the online booking site and soothsayer. "The further ahead you start to watch [fares], the greater the chance you'll see a downward bump."

The company released its Travel Cheat Sheet for booking holiday flights in 2018. It culled several years' worth of historical data to help answer the nagging question: How far ahead should I book for [insert name of holiday]?

"There are similarities between what the airlines did in the past and what they are going to do in the future," he said. "They are pretty predictable."

Though some variables can convulse airfares, such as a rise in oil prices, Surry said travelers should typically book their flights from three weeks to two months in advance, depending on the special day. For example, Martin Luther King Jr. Day (whoops, you missed this one), Presidents' Day (still time), St. Patrick's Day, Memorial Day, Fourth of July and Labor Day require the shortest window of time — at least three weeks ahead. For Easter and Columbus Day, the lead time jumps to six weeks. For Thanksgiving, start poking around for flights at least a month ahead. For Christmas and New Year's Eve, book no later than Oct. 30 and Nov. 5, respectively.

"For holidays, it's very rare to see last-minute price drops," Surry said.

Typically, prices fall in January and February, when traveler fatigue is high, and start to climb in June. For instance, round-trip domestic fares in January are 2.6 percent lower than last month, according to the study. The company highlighted several possible bargain spots in the States and overseas, such as Phoenix, San Diego, Shanghai, Delhi, Aruba and Morelia, Mexico. Surry also circled Europe.

"If you are thinking of taking that once-in-a-lifetime trip to Europe," he said, "this is a good time."

Several factors are yanking down fares to Europe. Demand is low, for instance, due to an increase in Americans sticking closer to home and a spate of terrorist attacks. There is also more competition in the skies, thanks to the emergence of low-cost foreign carriers such as Wow and Norwegian Air.

If planning ahead makes your head hurt, Surry suggests procrastinators zoom in on destinations that appeal more to leisure travelers (say, Hawaii and the Caribbean) than to business warriors (Chicago, Atlanta and Dallas). Airlines often hold back seats for desperado bookings and exact a high price for the short notice.

As for the age-old question of what are the best days to book a flight: Surry says Tuesday and Wednesday are still optimum, because airlines typically post flash sales midweek. But, he cautions, "You can't predict which Tuesday."