A friend of mine asked me today about a flight that she took from Washington, D.C. to Boston. The flight routed through New York City, and she was surprised to notice that she'd been credited with 500 miles for the DC-NYC flight and another 500 for the NYC-BOS flight. Here's an explanation that you can apply to your own travels.
Most of you are aware that airlines compute mileage as the straight-line distance between airports, so earnings are fixed even if a flight plan change is required (to avoid a storm, for instance). The mapped distance between Washington-Dulles (IAD) and Boston-Logan (BOS) is 413 miles. The legacy carriers have a 500-mile minimum credit, so had my friend taken a direct flight, she'd have been credited with 500 miles and nothing more.
What most people don't realize is that the mileage calculation--and the 500-mile minimum--is per segment rather than per flight. A segment is defined as a numbered flight with a set itinerary. Segments may include stops, but those stops don't impact the distance of the itinerary, so a flight from D.C. to Boston that had a listed stop on New York would also earn only 500 miles.
Here's how a flight with a listed stop might look:
Flight 213 IAD-BOS Depart: 12:00 p.m. Arrive: 1:30 p.m. Stops: 1 Miles: 413 Award Miles: 500
A large number of flight itineraries, however, are actually made up of multiple nonstop segments, each of which is calculated as a point-to-point distance for mileage purposes. Whenever the flight number changes, you've started a new segment--and that means you'll earn miles for each segment independently. And if those segments are shorter than 500 miles, they each receive the 500-mile minimum credit.
Here's a sample itinerary that includes multiple nonstop segments:
Flight 901 DCA-LGA Depart: 12:00 p.m. Arrive: 12:50 p.m. Stops: 0 Miles: 229 Award Miles: 500
Flight 417 LGA-BOS Depart: 1:05 p.m. Arrive: 1:40 p.m. Stops: 0 Miles: 185 Award Miles: 500
What does this mean for you? If you want to maximize your mileage earning, always choose a flight with multiple nonstop segments over one with listed stops. In many cases, the price is comparable, and you can come away with hundreds or even thousands of additional miles for the effort, often for spending the same amount of time in the air. The only difference is whether the time you spend on the ground is called a "stop" or a "layover."