Air travelers in the U.S. can expect a little price relief this summer, airfare data and forecasting website says. Its new Consumer Airfare Index evaluates and predicts the price of domestic air tickets for leisure travelers.

Airfare prices were down 9.7 percent on average in March, compared with the same month in 2014. And Hopper predicts that peak summer airfares will be 5.7 percent lower this year than they were last year.

"More Americans will be able to afford a summer getaway this year," said Patrick Surry, Hopper's chief data scientist. "We believe peak summer prices will be much cheaper this year due to how late and low prices bottomed out this winter relative to last year."

Of course, many of the price changes you can expect depend on what city you'll be flying from -- and where you'll be going. For example, fares from Dallas were up 21 percent from February to March of this year, while fares from Fort Myers, Florida, saw a nearly 5 percent decrease over the same time period.

And even though prices are lower on balance this year than they were last year, fares are still going up as summer approaches. Hopper predicts that May will have the largest monthly increase this spring, with airfares increasing by 7 percent. Prices will reach a peak in June.

The bottom line: Book your tickets for the summer as soon as you know where you plan to go.