I've often extolled the virtues of flexible travel date airfare search. The number of available seats at the lowest possible fare fluctuates minute by minute as customers book or release reservations, as the airlines adjust the number of seats available in each "fare bucket," and as they add or remove sale fares. Airfares also change depending on the day of the week or the month of the year. So consumers who have no specific dates they need to fly somewhere can save money by being flexible and searching for deals often.
But not all airlines offer a flexible travel date search function, and the number of online travel agencies and meta search travel sites that offer this capability has shrunk recently, with the latest casualty Hotwire.com, which just this week eliminated its flexible date search calendar. Travelocity (which, based on the Sabre global distribution system) once had the best flexible date search in the industry), Cheaptickets, Orbitz, and Expedia have all eliminated their 30-day (or longer) flexible date calendar searches, although they still give you the option of searching 1-to-3 days before or after the dates you choose. American Airlines (briefly) had a 30-day flexible date search but got rid of it as well.
While it's true that most people search for airfares by specific dates, for obvious reasons (they have a meeting, a wedding, a school vacation), other flyers really don't care when they go. A sales rep might want to establish a new face-to-face relationship with a client but only when the fare is cheap, or a grandmother might want to visit her grandkids whatever month it's most economical to fly and so on.
So what options still exist?
Only one metasearch site offers a true flexible date search function, and that's Kayak.com. Click on the "make my dates flexible" link, and then choose +/- 3 days, weekends, or flex month. You then choose your departure date and length of stay (maximum 7 days). Domestic and international fares are supported on most airlines (except Southwest and some non-U.S. discount airlines).
The only online travel agency left that offers a fare calendar function is CheapAir.com, but it's time-consuming to use because it will show you a calendar of dates when the fare is "valid" according to airline rules but could be sold out; so you have to hunt and peck. Also, it only covers some but not all domestic routes and no international ones.
Then there are the airline sites with flexible date calendars. These include:
United (click on the "My Dates are Flexible" button).
Hawaiian Airlines Click on the "See a monthly view of fares" link (the one in the very small typeface).
Spirit (searches automatically default to a fare calendar, which is unique in the industry)
So why don't more airlines and airfare sites offer a truly flexible date search option? For one thing, it's data-intensive. Each flexible search ties up more computer resources than a specific date search because there are more variables to crunch. And it could also be argued that there's no advantage to an airline to allow consumers to shop around for the lowest fare. Additionally, as a Travelocity executive explained to me many years ago, most people don't use flexible date searches anyway, so why offer it.
The stress on computing resources also explains why no website offers the holy grail of airfare search: let me enter my specific dates of travel (I want to leave on July 3 and return on July 10) now show me everywhere in the world I can fly at what price. That is truly a "find a needle in a haystack" data monster. Southwest Airlines briefly introduced this functionality but almost immediately disabled it (it's been "down for maintenance back very shortly" for months now).
One other flexible fare tool that should be mentioned is Google's Flight Explorer tool and its flight map function. Neither of these is a true "fare calendar" but they're fun to play with. (Like most of the tools mentioned here, they're powered by ITA Software, which Google now owns; you cannot book flights on ITA, but it's useful for finding flexible date fares).