Airline prices are constantly changing -- and that's why trying to score the best price can be an exercise in extreme frustration. Consumers can check a ticket price one day, be unsatisfied it and not buy, only to see it jump up the next day, and then come down again -- but not below the original price they found when they first started searching. It's impossible to know if you're getting the best deal.

Travel site Hopper unveiled its new Price Prediction mobile app on Wednesday, purporting to take some of the guessing out of when to book a ticket. By analyzing historical price data from thousands of flights, the app advises you on whether you should book a ticket now or wait for a lower price. What's more, you can set an itinerary for the app to monitor and you'll get real-time alerts when the price drops. 

"A lot of the flight alert products others are offering are almost a daily digest," Patrick Surry, chief data scientist at Hopper, told Mashable. But sometimes fares have already changed by the time people get those digests. "The real-time side of it is really important."

According to Hopper, spot-checking prices can cause consumers to miss out on the best deals. The Hopper app monitors prices constantly and sends out alerts when the price pf a fare is expected to rise or fall. On some routes, Hopper claims that its monitoring tools can help users save up to 40 percent. 

The app is only available for iOS 8 devices in the U.S. and Canada right now, though a spokesperson says that Hopper is working on developing an Android version, as well.