What is the difference between a legacy carrier and a budget airline?

The simplest way to tell them apart is what's included in the price. A legacy carrier sells you a seat plus a bundle of extras, and it can fly you almost anywhere by routing through hub airports. A budget airline sells you the cheapest possible seat and lets you add extras one at a time, usually flying point to point on popular routes.

What makes an airline a legacy carrier

Legacy carriers, sometimes called full-service or network carriers, are the older airlines that were already flying before US deregulation in 1978. In the US the classic legacy names are American, Delta, and United. They share a few traits:

• Hub-and-spoke networks. They funnel passengers through big hub airports, which lets them connect nearly any two cities with a single stop.
• Global alliances. Most belong to one of the three big alliances: Star Alliance, Oneworld, or SkyTeam. That means shared miles, lounges, and connections with partner airlines around the world.
• Bundled fares and cabin classes. Many fares include a seat assignment and a carry-on, sometimes a checked bag, and you can pay up for premium economy, business, or first.

What makes an airline a budget airline

Budget airlines, also called low-cost carriers, build everything around one thing: a low base fare. To hit that price they unbundle the trip and charge fees for seat selection, bags, priority boarding, and even snacks. They tend to fly newer, single-type fleets on point-to-point routes rather than through hubs, which keeps their costs down. Southwest is the giant of US low-cost flying, and in Europe names like Ryanair and easyJet lead the pack.

Low-cost vs ultra-low-cost

There's a second tier below the usual budget airlines: ultra-low-cost carriers, or ULCCs. Think Spirit, Frontier, and Allegiant in the US. They take unbundling to the extreme, so the advertised fare can look very cheap but almost nothing is included, sometimes not even a carry-on bag. A low-cost carrier is the middle ground, and an ultra-low-cost carrier is the strip-it-all-out version.

What this means for you

Compare the full price, not the headline fare. If you travel light and just need to get from A to B, a budget or ultra-low-cost ticket can genuinely be the best deal. If you're checking bags, want a specific seat, need a smooth connection to a smaller city, or care about earning miles and status, a legacy carrier's bundled fare may cost about the same once you add the extras, and it usually comes with more flexibility when something goes wrong.