An open-jaw flight is a roundtrip itinerary that arrives in one city but departs from another.
For example, an open-jaw itinerary could go from NYC to London, and then from Paris back to NYC. Open-jaw flights allow travelers to see two destinations in one trip without backtracking to the initial destination to catch their flight home.
You can also reverse the situation, where you fly from Point A to Point B, then return from Point B to Point C. For example, you might fly from Boston to London, then return from London to New York, then take the train or bus back to Boston. Sometimes you might find cheaper flights this way, which can save you money even if you have to pay for an extra transportation ticket back home.
Technically, open-jaw flights are a variation on multi-city flights, with one key difference: multi-city itineraries include the flight between cities, while open-jaw itineraries do not.
In the example above, if you’re flying to London but home from Paris, you’d need to book a separate flight (or train, bus, etc) between London and Paris. In many cases, if you try to make an open-jaw into a multi-city itinerary (by adding a flight between the two cities) it becomes much more expensive.
A double open-jaw flight goes from Point A to Point B, then returns from Point C to Point D. For example, flying from Detroit to London, then returning from Paris to Chicago.
Open-jaw flights are not necessarily more expensive than traditional there-and-back roundtrip flights. There are a lot of factors at play, including the routes and the time you plan to travel. Some open-jaws might actually be less expensive than a traditional roundtrip.
When traveling internationally, however, it’s important to note that open-jaws are almost always cheaper than two separate one-way flights.
You can book open-jaw flights by using an airline’s multi-city booking function. That way, both flights will be under the same reservation.