Decades ago a round-trip was almost always cheaper than two one-ways. Today, with low-cost carriers and one-way pricing on many airlines, it depends on the route.
When two one-ways win
- Short- and medium-haul routes served by low-cost airlines, which price each direction separately.
- When the cheapest outbound and return are on different airlines.
- When you want to fly into one city and out of another.
When a round-trip wins
- Many long-haul routes on full-service airlines, where one-ways can be priced close to a round-trip.
- When you value one booking for changes and disruption handling.
The risk
Two separate tickets are two separate contracts. If your outbound is cancelled, the other airline won't adjust your return. Use flexible fares or leave buffer days if that would hurt. Always price both ways before you book.