Flexible travel date airfare search is the best way we know how to save money on air travel. In fact, it's the principle on which Airfarewatchdog.com was founded.

No discussion of flexible date airfare search can exclude ITA Software’s Matrix Airfare Search function; and although it's much beloved by airfare hounds, read why it shouldn’t be relied on as the Holy Grail of Search.

ITA Software is neither an online travel agency nor a meta-search site. Instead, it’s the airfare search “brains” behind many online travel agencies, airline websites and meta-search sites.

You cannot book airfares here, so once you find what looks like a good airfare you have to try finding it on an online travel agency site, airline site, or meta-search site; but you can use its powerful search functions to locate possible airfares and it has a lot of advanced features that airfare geeks plotz over. The “simple search option” link is very easy to use. Enter a departure and destination airport, click on “See calendar of lowest fares,” choose a departing month and a length of stay, and hit search.

But while this is a useful tool, too many “fare hackers” put blind faith into it. As the case with all third-party airfare search tools, it’s not infallible, in part because no airfare search tool includes “airline-site-only” fares and none of them allow you to enter promo codes. Case in point: on Nov. 8, 2012 South African Airways sent out an email alert to subscribers advertising fares to Africa from Washington and New York for $860 roundtrip including tax, an amazing deal (in fact, it was an Airfarewatchdog “fare of the day”. Searching on the airline’s site, I was able to book Washington Dulles to Capetown for $889 roundtrip leaving on Nov. 11 and returning on Nov. 27. Moreover, the outbound was a direct flight with one stop, the return nonstop. So I tried a search on ITA for the same flights and dates. The lowest fare was indeed on SAA, but for $1232 and the only option shown at that fare required two changes of plane in each direction. For the record, searching the same flights/dates on Expedia showed a lowest fare of $936 with two stops in each direction. And Kayak showed the same results as Expedia, unless you clicked on a box specifying South African Airways, which opened a new window, in which case you’d see the SAA.com-only fare.

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