Cheap plane

If you’ve spent any amount of time shopping for flights, you probably know that airfares change a lot. Airlines will tell you that the price fluctuations are based on meticulous real-time calculations to match supply and demand, but to travelers the ups and downs seem random, totally unpredictable, and utterly without rhyme or reason.

Whether there is really a method to the madness or not, everyone just wants to know one simple question: when is the best time to buy an airline ticket?

To answer that question, we looked at 1, 336, 030, 117 air fares (that’s about 1.3 billion) as part of our annual air fare study. Since “it’s complicated” doesn’t make for a very good headline, we’ll start by focusing on a bottom line number, and that number is 54 days. That was, on average, the best number of days in advance to buy a flight in 2015, for travel within the U.S.A.

The reason it’s a little more complicated than that, though, is that every trip is different. While 54 days in advance might have been the average best time to buy based on everybody’s trips last year, that doesn’t mean it will be the best time to buy for your trip this year.

In our study we looked at 2, 926, 668 “trips”. That’s just under 3 million. We defined a “trip” as an itinerary going from Point A to Point B on a specific date with a specific return date. For each trip we looked at the lowest fare offered for that trip every day from 320 days in advance until 1 day in advance.

If you look at all 3 million itineraries, the best times to buy were all over the map (no pun intended). For a lot of them (about 13, 000 in total) 54 days out was indeed the best time to buy, but for almost as many the best time to buy was 53 days out, or 52 days, or 45 days, or 60 days. In fact, for almost 30, 000 trips the best time to book was actually the day the flight first went on sale! And for a fraction of them (a tiny, tiny fraction) it was best to book at the very last minute.

The point is there is just no one magic number that you can rely on to create a calendar reminder x number of days in advance and know that that day is the best day to book. We can say, though, that there are some general rules that do usually hold up (except for super-busy holiday times where all the rules go out the window.)

As you move from the time a flight initially opens for sale, to the day the flight departs, we see a pattern of how fares change – typically starting off high, slowly coming down, and then a few weeks before flight time starting to climb, with a particularly sharp increase once you’re inside 14 days.