What is the cheapest day to fly with Southwest Airlines? Southwest Airlines is already a low-cost airline that is known to handle passengers' expenses and save a lot of money. At the same time, passengers who are looking for the airline to book the tickets in such a way that the airline does not compromise with the comforts of travel but also is affordable, their research ends with Southwest Airlines. However, if you want to make your travel even more affordable with Southwest Airlines then here are some tips that will give you the information on the best time to buy tickets on Southwest Airlines which are mentioned further in this article. Knowing the Best and Cheapest Days to Book Southwest Airlines! When finding the best time to book Southwest Airlines then it is Tuesday afternoon. As it is the day of the week when Southwest Airlines starts their ticket sale. And Tuesday afternoon is the best time because it is the time when sales are not known and the prices are affordable