Can your frequent flyer miles really get you to where you want to go?

Members of frequent-flyer programs often spend lots of time trying to build up miles with one goal in mind: a free trip to somewhere great. Some people might even go far out of their way to earn extra points. Watch our video on snagging frequent-flyer miles.)

Today there are more than 70 frequent-flyer programs worldwide with more than 300 million members, says Tim Winship, the editor and publisher of FrequentFlier.com, a website that helps travelers navigate those programs. As a very general rule, he says, 5 percent of airline seats are allocated for frequent-flyer awards. And since the early 1990s, the number of miles needed for most domestic round-trip tickets has remained steady, at 25,000.

But when you actually try to book a seat, you face some major hurdles. For one thing, you have to deal with lots of competition and blackout dates (days during high-traffic seasons when award seats are limited or unavailable). Every program has its own policies, procedures, and partnerships with other airlines, as well as status tiers that can affect your booking success. And the programs are constantly changing. United Airlines and US Airways, for example, recently increased the number of miles needed to book some of their coach, business-class, and first-class seats.

Airlines may also require more miles to book popular routes or during busy travel seasons, says George Hobica, founder and president of Airfarewatchdog, a comparison site. And if an airline hasn’t sold enough seats on a flight, it might add more award seats at the last minute.

So when is the best time to book a free trip? To find out, we recruited Consumer Reports staff who are members of frequent-flyer programs with nine airlines: Alaska, American, Delta, Frontier, JetBlue, Southwest, Spirit, United, and US Airways. We asked them to try booking a round-trip coach ticket on the same day for the five most popular U.S. routes: Chicago to New York City, Los Angeles to San Francisco, Los Angeles to New York, Chicago to Los Angeles, and Atlanta to New York City. (Alaska, Frontier, and JetBlue don’t fly all of those routes, which was taken into account when we crunched the numbers.) The flights left on a Friday and returned on a Sunday, two of the busiest days for airlines.

The testers searched for seats on each route for three dates: flights that departed in three days; those that left in a month; and those that took off in three months. Then they filled out questionnaires, noting how many flights they could book (if any), the fewest miles they needed to use, and how long each leg of the trip would take. They also noted how many stops they would have to make (if any), the fees they would be charged to book, and how easy it was to navigate the airline’s website. Of course, our results are a snapshot based on the dates and routes we chose, but some themes did emerge.

Airlines that charged the most

On average, Spirit required the most miles for all of the routes we checked, followed by US Airways. We found that those two carriers also charged the highest booking fees: Both pinged our testers $111 to fly on a few days’ notice.  

Those that charged much less

Alaska Airlines had the best mileage deals, on average—less than half of the miles needed to fly on Spirit—followed by JetBlue, American, and Delta. Those four airlines and Southwest charged a flat fee to book (see the chart on the bottom of this page), with one happy exception: Alaska Airlines, whose fee dropped to $23.70 from $36.20 for our last-minute trip from Chicago to Los Angeles. But those savings were canceled out because the airline upped the mileage required for the same route. Chicago to Los Angeles was also the only route on Alaska Airlines that cost us more than 25,000 miles, coming in at 32,500.

Most available seats

Delta, the nation’s second-largest carrier in terms of market share, had the most available flights, followed by Southwest (the third-largest airline in the U.S.), and US Airways (now part of the nation’s largest airline group because of its recent merger with American).

Most airlines have alliances with other carriers, which increases your odds of booking a seat. For example, although Alaska doesn’t fly every route we checked, we were always able to find a seat because of its partnership with Delta.

But some of the airlines with the best mileage deals were also harder to book. When we tried to use miles to nab flights that departed in three days, for example, we were unable to get a seat on returning flights on three Alaska routes, four out of five on American, and one on United. Frontier had no seats on the Chicago-to-Los Angeles route. Spirit had no award seats available on either leg of one route (Los Angeles to San Francisco) and offered no return flights on that route for both of our later departures.

Find out the 9 ways you can increase the odds that you'll be able to book a seat using your miles.

Best for booking far ahead

JetBlue, Southwest, and US Airways tended to significantly increase the number of points needed to book at the last minute. On Southwest’s Chicago-to-New York route, for example, the points needed for a round-trip ticket went from 17,648 miles a month before departure to 77,582 for a flight three days away. (See the chart for more examples on the Los Angeles-to-New York route.)

Best for last-minute travel

United was the only airline that sometimes lowered the number of miles needed to book a seat close to the departure date. For example, the 50,000 miles needed for a Chicago-to-New York City flight in one or three months dropped to 25,000 miles for a flight leaving in three days.

Most consistent

Delta had little fluctuation in miles for each route. It would have set our tester back 32,500 miles in every case except the Chicago-to-New York route (25,000) and on flights from Los Angeles to New York City or San Francisco when booking three months in advance (also 25,000).

The number of miles that Alaska, American, Frontier, and Spirit charged for seats was also relatively flat, with a few notable exceptions.

Alaska bumped up the number of miles for last-minute travelers flying from Chicago to Los Angeles from 25,000 to 32,500. Spirit passengers leaving Chicago and heading to New York City would save 15,000 miles if they had booked three months in advance instead of waiting a month or less to use their miles.

In July, Consumer Reports had staff members in frequent-flyer programs try to use their points to book round-trip coach flights on five of the most popular routes in the U.S. The charts show what happened when they attempted to book round-trip flights on nine airlines three, days, one month, and three months in advance. (Note: Although American and US Airways have merged, they were still operating separate websites and reservation systems during our test.)

From Chicago to New York and back

From Los Angeles to San Francisco and back

From Los Angeles to New York to and back

From Chicago to Los Angeles and back

From Atlanta to New York and back