Two one-ways are not always two one-ways

There is a short answer about one-way versus return tickets and a useful one, and they are not the same. What follows is the useful one.

Two pricing traditions

Low-cost carriers price every flight independently, so a return costs the sum of its parts and a single carries no penalty. Network carriers historically priced round trips as a product, which made a one-way disproportionately expensive on many routes.

That distinction has softened, and many network carriers now sell one-ways at half the return price on short routes. On long-haul the older pattern persists more often, which is why a single long-haul leg can cost close to a full return. The only reliable method is pricing both structures for your specific route rather than applying a remembered rule.

What a through ticket protects

Two flights on one ticket make the airline responsible for the connection, including rebooking when the first runs late. Two separate tickets create two contracts, and missing the second because the first was delayed is entirely your loss.

That protection is why a slightly more expensive through fare frequently costs less once the risk is priced in. It also affects baggage, since separate tickets usually mean collecting and rechecking bags at the intermediate airport. Where the connection is long and the airport simple, the risk is small; where it is tight, it is the whole decision.

Where singles win

Open-ended trips whose return date is genuinely unknown are the clearest case for buying one leg at a time. Mixing carriers can be much cheaper when one airline dominates the outbound market and a different one dominates the return.

From the queue, singles also make it easy to fly out from one airport and home to another, which a rigid return will not allow. They avoid the situation where changing a return fare costs more than the original ticket did. The cost is carrying the risk that the return fare rises, which on popular dates it very reliably does.

The open jaw

An open-jaw itinerary flies into one city and out of another, with the gap between them covered by your own arrangements. Many network carriers price this as a return rather than as two singles, which makes it far cheaper than most people assume.

In practice, it suits any trip that moves in one direction, which describes most journeys involving overland travel between places. It also removes the wasted day spent returning to the arrival airport purely in order to fly home from it.

Search tools support it under a multi-city option, which is the tab most travellers never open.

Immigration and the onward ticket

Some countries require proof of onward or return travel as a condition of entry, and airlines check this before boarding. A one-way ticket can therefore be refused at check-in even where the immigration rules would in fact have permitted entry.

The working rule: the requirement is set by the destination and enforced by the carrier, which is why the two occasionally appear to disagree. Holding a cheap onward ticket, a rail booking or a bus reservation usually satisfies it, though the rules differ by country. Checking this before buying a single is the step that turns a cheap fare into a fare you can actually use.

A method rather than a rule

Price the return, price two singles, and price the open jaw, which together take a few minutes on any search tool. Add the value of flexibility when the return date is uncertain, since a change fee is a real and predictable cost.

Subtract the value of connection protection whenever the itinerary involves changing aircraft along the way. Check the entry requirement before committing to a single into an unfamiliar country. The answer differs by route and by season, which is exactly why a fixed rule performs so badly here.

The takeaway

Price all three structures, then pay for the protection or the flexibility you actually need.

The trip goes better when the bag is boring.