Economic and Operational Implications of the Leap Second and its Cancellation

Leap seconds are one-second adjustments added to Coordinated Universal Time (UTC) to keep it within ±0.9 s of Earth’s rotational time (UT1), i.e., to synchronize atomic time with astronomical time. Since 1972 there have been 27 positive insertions, the last on 31 December 2016. In November 2022 the General Conference on Weights and Measures (CGPM) adopted a path to phase out future leap seconds by or before 2035, moving toward a continuous UTC. This article consolidates documented operational incidents and presents a back-of-the-envelope economic assessment of leap-second events. We find that a single leap second plausibly exposes the global economy from the low tens of millions up to about USD 100 million in direct disruptions, with tail risks concentrated in finance, aviation, and large-scale internet platforms.Removing the leap second reduces coordination burden and eliminates a rare but brittle failure mode—especially salient given the prospect of a possible first-ever negative leap second.