Just as it’s impossible to predict the stock market (why aren’t all those Wall Street prognosticators richer than Midas by now?), anyone who pretends to know whether airfares are headed up or down is just fooling with you. There are just too many variables, and airlines are just too capricious to allow themselves to be outguessed.

That said, over a dozen web sites will tell you when a fare on a route has gone down in price. They provide this service for free, and it’s the absolute best way to find a deal. Only caveat: you have to work fast. The best fares get snapped up and some deals last only for a matter of hours, or even minutes.

Lest you think that you can just sign up for one of these alerts services, you should know that they all work a bit differently. And lest you think that as the creator of Airfarewatchdog.com I’m a completely unreliable source, I’ll say that sites we’ve analyzed do a better job than we do in some respects. (Did I really say that? Um, yes, I did).

How do the various sites differ? For starters, some don’t all track every possible route or airline. Most don’t monitor fares on Southwest Airlines or uber-discounter Allegiant (to its credit, Airfarewatchdog does).

But what if you really only want to fly on the 9 a.m. Virgin America nonstop to Los Angeles? Or you only want to monitor nonstop flights on Delta? Then you probably don’t want to use Airfarewatchdog or Travelocity’s FareWatcher Plus, since these sites generally track only the lowest fare found, irrespective of specific travel dates, airline and other niceties. That’s where sites such as Farecompare.com, Bing.com/travel, or Yapta.com come in handy. For instance, with Yapta, after you search for a fare on a specific departure and route, you can choose to monitor only that flight. Just beware that if you are hoping that the 9 a.m. nonstop will go down to an affordable price and it remains stubbornly unaffordable, you may decide not to fly at all. So keep your options open and sign up for as many departures as possible.

To recap, if you’re flexible in your travel dates and want to visit an important client or a beloved relative only when the price is lowest, sign up for alerts that show you the lowest possible prices using a flexible travel date paradigm. Similarly, if you don’t even know where you want to go, but just want to go somewhere cheap, there are alert sites for that, too. But if you’re the picky sort and only fly United Airlines nonstops leaving between 9 a.m. and 10 a.m., and price is less important than convenience or frequent flyer points, then there’s an alert site for you, too. Please do take a look at the handy chart we’ve compiled, and if you find an inaccuracy (because, frankly, these alert sites can be pretty complex and do add new features), please leave a comment.

All products and services mentioned on Airfarewatchdog are independently selected by our team of expert travelers. If you buy something through our links, we may earn an affiliate commission.

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