BOSTON -- Knowing how far in advance you need to buy a ticket on your next flight could save you a lot of money. Here's a site that may help you predict what a flight will cost depending on when you book it.

FareCast.com will tell you where fares are going and show you where they've been. Just choose your departure and arrival cities and the dates you plan to travel.

The site will give you a list of flights from dozens of carriers. FareCast will then predict what the chances are that a specific flight will go up in price over the next few days.

Right now, the site offers information only on flights out of Boston and Seattle, but new cities will be added during the rest of the year.

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