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International Bureau of Weights and Measures Officially Abolishes Leap Second, Effective 2027

Confirmed1 source · Oct 16, 2026

The BIPM voted to end the practice of adding leap seconds to atomic time, citing the rising risk of a negative leap second and decades of technical problems for computer systems.

International Bureau of Weights and Measures Officially Abolishes Leap Second, Effective 2027
Image via Wired

What happened

The International Bureau of Weights and Measurements (BIPM) announced Thursday that it will stop issuing leap seconds beginning May 20, 2027. Leap seconds have been added 32 times since 1972 to keep Coordinated Universal Time (UTC)—measured by atomic clocks—aligned with Universal Time (UT1), which is based on Earth's rotation. The announcement was prompted in part by the rising probability of a negative leap second, with a 2024 Nature study indicating one may be required as soon as 2029 due to Earth's accelerated rotation caused by climate-related shifts in planetary gravity and melting ice.

Context

Leap seconds exist because Earth's rotation is gradually slowing due to tidal friction, the moon's gravitational effects, and dynamics in the planet's molten core, oceans, and atmosphere. However, recent years have seen the opposite—Earth's rotation accelerating—creating the novel problem of potentially requiring a negative leap second, which has never been tested and raised concerns across technology industries. Leap seconds have repeatedly caused system failures in critical infrastructure: Qantas's booking system was disrupted in 2012, and many other UTC-dependent systems have experienced problems despite workarounds like Google and Meta's 'smear' method of spreading the adjustment over a day. By eliminating leap seconds, BIPM removes the need to manage these increasingly complex adjustments, though this means UTC and UT1 will gradually drift apart. The agency has committed to implementing a leap hour in the distant future—thousands of years hence—to eventually resync the two time systems.