Source: Data from CheapAir.com.
Airlines are practicing a yield management strategy where the airfare will vary as the date of departure approaches. At the aggregate level, it appears that 54 days before the flight offers the lowest fares and that fares are the lowest within a 30 to 100 days window. The most expensive time to book airfare is the day before the flight is scheduled, mainly if it is almost fully booked. Airlines are capitalizing on the willingness of last-minute travelers to book a specific flight (often for urgent personal or business purposes where the price is of lesser consideration). Airfares are constantly changed to reflect the dynamics between supply and demand. On average, in the United States, the airfare on a specific flight will be changed 92 times between the time seats are first made available and the departure time.