All low-cost carriers have the most expensive tickets on Sunday (15-20% more expensive than the average price) and the cheapest tickets on Tuesday and Wednesday (15-20% cheaper). Flying on Friday and Saturday will cost you 5-10% more. Although, for example, at Ernest Airlines, the difference between days of the week varies only within 5%.
For scheduled airlines, the direction of travel and the number of days between flights also matter. For example, a ticket departing and returning the same day will cost about 15% more and returning the next day will cost 5% more, almost regardless of whether you fly on Tuesday or Sunday.
For longer trips, the most expensive option is to fly out on a Saturday and return the following Saturday or Sunday. Slightly cheaper is a two-day trip Friday-Sunday. The cheapest option (average 10% savings) is to fly out Tuesday through Thursday and return 5-6 days later (but not Sunday). Interestingly, 7-day tickets even with a Wednesday or Thursday departure will not save you much.
The above-mentioned flight direction implies a difference in demand in finding a route from point A to point B and vice versa - from point B to point A. For example, on the Warsaw - Milan route, approximately 80% of travelers book tickets with the first segment from Warsaw to Milan and return to Warsaw. Accordingly, the same two-day trip Friday-Sunday Warsaw - Milan - Warsaw will cost you on average about 5% more than the same trip on the route Milan - Warsaw - Milan. Similarly, tickets Warsaw - Milan - Warsaw from Sunday to Saturday will also be about 5% cheaper than tickets for the same dates Milan - Warsaw - Milan.
Rule #3. High and low season
For scheduled and low-cost airlines, this translates more into changes in the schedule of the flight program in winter and summer than into changes in prices. Usually airlines have a winter schedule from the end of October to the end of March and a summer schedule from the end of March to the end of October. And the frequency of flights to certain destinations can vary significantly. This balances the demand and price for all destinations, but still sometimes prices in the high season can differ many times, especially for popular destinations.
High season is summer vacation (June - August), Christmas and New Year (mid-December - early January), Easter vacations (March or April). During these periods, there is a good chance that tickets are optimally inexpensive if purchased 3-5 months in advance.
Low season is the period from mid-January to early March (excluding winter vacations), mid-April to mid-June, and September to mid-December (excluding fall vacations). During these periods, airfares are usually more affordable and it is possible to find good deals even if you book 1-2 months before departure.