International Timekeepers Expected to End Leap Seconds by 2027

Delegates from the 69 member states of the International Bureau of Weights and Measures are meeting this week in Versailles to decide whether to abolish the leap second. The leading proposal would take effect on 20 May 2027 and would permit Coordinated Universal Time to diverge from astronomical time by as much as one hour before any adjustment is required.

Leap seconds have been inserted occasionally since 1972 to keep atomic clocks within 0.9 seconds of the Earth’s rotation. Twenty-seven positive leap seconds have been added; the most recent occurred on 31 December 2016. In recent years the Earth’s rotation has accelerated, raising the possibility of a negative leap second in which a clock would skip from 23:59:58 directly to 00:00:00. No negative leap second has ever been tested in live global systems.

Technology companies have long warned that leap seconds create risks for networks, financial systems, and GPS. Meta stated in 2022 that every leap second is a major source of operational difficulty and that a negative leap second could have a devastating effect on software. The BIPM’s governing body decided in 2022 to end the practice by 2035. The current proposal accelerates that timeline because of the elevated chance of needing a negative leap second within the next decade.

Under the draft resolution, the maximum permitted difference between UTC and the Earth’s rotation (UT1) would rise from 0.9 seconds to 3,600 seconds. Once the accumulated drift reaches one hour, a single planned leap hour would be applied. Scientists estimate that, at present rates of slowing or acceleration, such an hour-scale correction might not be needed for centuries or longer. The change would keep atomic time continuous for practical purposes while decoupling everyday clocks from the precise length of the solar day.

The 28th General Conference on Weights and Measures is scheduled for 13–15 October. If the resolution passes, national timekeeping authorities would implement the new rule from World Metrology Day 2027. No leap second is currently scheduled for the end of December 2026. The IERS has confirmed that none will be introduced at the close of this year.

Some observers have noted a philosophical objection: the change would allow civil time to drift gradually from the observed position of the sun. Supporters argue that clocks are already artificial and that the operational risks of abrupt second-scale adjustments outweigh the benefit of keeping civil time within one second of solar time. The outcome of the vote will determine whether the next generation of global systems must prepare for a negative leap second or can plan for decades of uninterrupted atomic time.