This Is The Best Time to Buy A Plane Ticket
Dan Bannister

This article originally appeared on Fortune

Most travelers know they should purchase plane tickets in advance if they want to save money on seats. But too much preparation can actually lead to a more expensive flight.

A new study from has revealed that the best time to buy a domestic plane ticket is, on average, 54 days before the scheduled flight.

The study found that “first dibs” tickets — six to 11 months in advance — tend to be on the higher side, as flights have just opened and airlines are less desperate to make sales. Even “peace of mind” tickets — three and a half to six months in advance — can have moderately pricey fares, though there are typically more affordable fares than first dibs. Three weeks to three and a half months is the “prime booking window.” Any shorter and you’ll “push your luck” (two to three weeks) or risk a “Hail Mary” (zero to two weeks).

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“The most important rule is fairly obvious: don’t wait until the last minute, as that rarely works out,” Jeff Klee, CEO of CheapAir, said in a statement. “But beyond that, you also want to be careful not to buy too early. I always suggest that travelers check fares early and often and get familiar with the market. Then, when you see a good deal pop up, grab it, because it likely won’t last very long.”

CheapAir found that the fare for a flight changes an average of 71 times between its opening and the day it takes off. That’s an average price change of every four and half days at a rate of $33 up or down.

To obtain the results of the study, the company said it surveyed data from 921 million airfares from 2.9 million trips.