Round-trip tickets cost a bit under twice the one-way fare, except in the first year of the pandemic, when the premium shrank. It has stayed in a narrow range since.
What this shows: The chart covers 2020 Q1 to 2025 Q2. It plots Round-trip to one-way fare ratio and Round-trip share on a vertical axis of Ratio / share. Latest values: Round-trip to one-way fare ratio 1.717; Round-trip share 0.5636. Data run through 2025 Q2.