Book Early

• Book airline tickets at least 21 days in advance. Flights booked three or more weeks ahead of time are advance-purchase tickets and tend to be more reasonably priced. Prices begin to rise after this three-week time frame. The fares go up again 15 days in advance and once more seven days before the flight.
  
  

But Not Too Early

• Do not buy your airline ticket more than four months in advance, unless you are flying around a major holiday and want to lock in a reservation. Four or more months before a flight, there is no competition yet with other airlines, so carriers do not have the incentive to offer discounted rates.
  
  

Wednesday, Early Morning

• Try to book flights between midnight and 1 a.m. in the time zone of the airline's headquarters. Many people will search for flights, find a discounted fare and begin to book it. They will go all the way to the payment step of the purchase and then stop. The airline's computer systems will hold on to these tickets as 'reserved but unbooked.' Most airlines have their systems set to release these tickets, many of which were selected because of the discounted rates, between midnight and 1 a.m on Wednesday.
  
  

Find a Sale

• Airfare sales tend to take place earlier in the week, and airfare rises later in the week. While many people look for and book flights on Tuesdays, it is a myth that flights are cheapest on Tuesdays. Watch for airlines to offer sales, or sign up for email notifications. Airlines will email you when fares go on sale.
  
  

Travel Wisely

• Regardless of when you book your ticket, it is almost always cheapest to fly on a Saturday. The most expensive day to fly is Sunday. Airlines know that weekend travelers want to start their weekend on Friday. If you can travel on Saturday instead, you will find a cheaper fare. Airlines also know that weekend travelers will be flying home on Sunday. If you can fly back on Monday, you'll save yourself some money.