TORONTO — The magic number is 54. 54 days before takeoff is, on average, when domestic airline tickets are the lowest you will see. However if you miss the magic 54 number, it is recommended that you book between 112 to 21 days before departure, which is the “prime booking window” to secure the lowest possible prices.

Staff at CheapAir spent 2015 analyzing three million airline trips, tracking ticket prices from 320 days before departure all the way to the day before takeoff. The calculated which day each ticket hit its lowest price point.

Their findings have shown that booking last minute does not save travellers money, in fact, it is more costly. Researchers discovered that on average, a ticket costs about $200 more when booked within seven days of departure, compared with tickets booked in the “prime window.” Those who bought tickets between seven and 13 days before departure paid about $75 more.

Even though 54 is the magic number, the best price for your flight depends a lot on the specific trip you are taking. Going somewhere popular at a popular time, such as spring break in Florida, shows that you should book before the “prime booking window.” When a flight has constant and strong demand, airlines are less incentivised to lower ticket prices as time goes on. This rule also applies to flights to hard-to-reach airports in small cities, where little airline competition leads to less price drops in ticket fares.