You should always book one-way tickets, except when you shouldn't

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Not just among travel hackers, but also in the civilian population, the conventional wisdom for a long time has been that it's usually better to make roundtrip airline reservations than book one-way tickets. There are a few reasons usually cited for this:

  • In the case of a trip interruption or cancellation, you'll only pay change fees once on a roundtrip ticket booked on a single reservation, while you'd have to pay the corresponding fee in each direction if the tickets are booked separately.
  • Since "only business travelers book one-way tickets," airlines take advantage of the opportunity for price discrimination to charge more for one-way tickets than roundtrip reservations. They may charge less for tickets with a Saturday night stay, a discount you can only secure if you book a roundtrip ticket.

I book virtually all of my airline reservations as one-way tickets these days, and thought it would be worth explaining why.

Some airlines compose all reservations from one-way segments

Alaska Airlines and Southwest Airlines treat all reservations as the combination of two or more one-way tickets. So you'll never save any money booking a roundtrip ticket on those airlines, rather than two one-ways.

In an extreme case, if you're tracking the price of your Southwest Airlines reservation in order to rebook at a lower fare, you might miss the opportunity if your outbound segment goes down in price and your return segment goes up in price by the same amount or more.

Keeping your reservations separate will make sure you capture any downward price difference in either direction.

Some airlines don't let you change your frequent flyer information after travel has commenced

If you want to credit one segment of a Delta-operated itinerary to SkyMiles and another to Alaska Mileage Plan, you're out of luck: once travel has commenced, you can't change the frequent flyer account linked to a Delta-operated reservation.

If you make two reservations instead, you can easily credit one of them to one airline's frequent flyer program and another to a second program.

Booking one-way tickets allows you to capture low-level redemptions, where available

Consider a $600 ticket, the individual components of which price at $350 each. While the roundtrip ticket is $100 cheaper than two paid tickets, if low-level award space is available on one segment, but not the other, you can buy one $350 paid ticket and redeem 12,500 miles, getting 2 cents per redeemed mile.

And of course, you can redeem 20,000 US Bank Flexpoints for the $350 ticket, which brings me to...

Price compression means more expensive tickets don't necessarily cost you any more

In the case above, the $600 roundtrip ticket (well, assuming it's actually $600.01) will cost 40,000 US Bank Flexpoints. But two $350 one-way tickets will also cost 40,000 Flexpoints! Furthermore, booking the tickets separately may reveal that a first class ticket in one or both directions costs only marginally more, allowing you to book yourself in greater comfort (and in a higher-earning fare class) without redeeming any additional miles or points. That's the phenomenon I refer to as "price compression."

When you should definitely consider booking roundtrip reservations

There are a few key exceptions to my rule of thumb that most trips should be booked as a series of one-way reservations:

  • Complicated reservations. If you're booking multi-stop itineraries in one or both directions, you want to be accommodated if you miss a connection or a flight is cancelled. If your airline can't see your onward connections in their system, they probably won't accommodate you.
  • If you're booking a revenue ticket in either direction of an international itinerary. With all of its marvelous pricing technology, the airline industry often charges less (sometimes much less!) for roundtrip tickets to and from Europe than for one-way reservations. So make sure you're actually saving money before booking one direction with cash and the other direction with miles and points.
  • If you are buying travel insurance (and actually might use it). If you buy two one-way tickets, and your outbound trip suffers an event covered by your trip insurance, your return flight may not be covered. In any case, it means paying two trip insurance premiums for a single trip and a single covered event.

Conclusion

There are obviously a lot of moving pieces here, but the key take-away is to check the award and revenue pricing for all flight reservations as both one-ways and roundtrips. You may end up saving a lot of whichever currency you end up deciding to use.