We estimate the switching costs created by tier levels, one of the main components of airline frequent flier programs, by exploiting discrete tier thresholds. We first demonstrate that travellers increase their demand to reach a higher tier level just before the end of the calendar year when tier levels are determined, but do not manipulate demand in earlier months. This allows for a novel fuzzy discontinuity approach to identify causal demand effects of higher tier levels, from which we derive the airline switching costs. While the lowest level creates only negligible switching costs, the switching costs associated with the highest tier level are in the range of 30%–41% of the price of a ticket, representing an important determinant of travel behaviour in airline markets. These results especially provide evidence of the use of tier levels to induce loyalty from high-frequency travellers for whom free flight awards alone would not create substantial switching costs.