Log in to Yapta.com, Kayak.com or Sidestep.com. Bing Travel and Fare Compare provide a similar service.
Start a trip search. Choose your departure and arrival airports and dates, then search for flights.
When the current search results come up, click on the "Fare Charts" link on the top of the left sidebar to see how today's price compares to price trends in the days and weeks surrounding your trip. Another graph shows how the ticket price has fluctuated in the past three months. By paying attention to these trends, you will see what a good low price would be and whether or not that price has been offered yet. Bing Travel will give you a "Price Predictor" that advises you on whether to buy the ticket now or wait, given the tracking information.
Enter your email address for notifications when the price of the flight changes. You can also log back into the website and refer to your saved searches to see the flight price later.
Search again using the "Flexible Dates" option to see how the price of the trip changes if you fly a few days sooner or later. The sites listed above provide one-week to one-month calendars for tracking prices.
Log back in at different times on different days of the week to continue tracking the flight price, or just read your tracking emails from the appropriate websites. Fare Compare suggests that the best time to purchase tickets is on Tuesdays at roughly 3 p.m. Eastern Time, according to its historic airfare research.
