iming is everything -- especially when you're trying to score cheap airfare for your summer vacation.

Getting a good price on airline tickets is an art form. flight trip tracker And a mystery. Do you buy months ahead of time when there are choices galore? Do you wait until the very last minute, when airlines might be desperate to fill empty seats? Do you buy on Tuesday, the day airlines have traditionally posted sales? Each of these strategies has its adherents.

The truth of the matter is a little more mundane.

"The best prices on average are in the 21-day to 4-month window for domestic U.S. airline tickets," CheapAir.com's 2018 "When to Buy Flights" study states.

If you want to be more specific than that in your quest to land the best deal: The study concluded that in 2017 the best time to buy airline tickets, on average, was 70 days before your departure date.

The year before that the best time to buy was 54 days before the flight.

Buying before or after that sweet spot usually will cost you. "If you're going to buy early, you should know that you're going to pay a premium -- around $60 more if you buy 6–11 months out," CheapAir.com writes.

And the online travel agency calls buying tickets the week before a flight "the Hail Mary zone," finding that ticket-buyers will pay on average $170 more per ticket for purchasing at the last minute.

The study crunched the numbers on "917,000,000 [airfares] in more than 8,000 markets."

An interesting tidbit from the survey: The lowest fare for an average flight changed 62 times during the time the flight was on sale.