Leap seconds to end in 2027, helping computers stay in sync

International timekeepers have approved an end to leap seconds from 20 May 2027, a change designed to reduce computer glitches and make timekeeping more reliable. The General Conference on Weights and Measures, meeting in Versailles, brought the planned change forward by eight years.

Leap seconds keep Coordinated Universal Time, or UTC, the world's reference time, closely aligned with Earth's rotation. Atomic clocks measure time with exceptional consistency, but the planet's rotation varies slightly. Since 1972, 27 extra seconds have been added to bridge that gap, most recently in December 2016.

Those tiny adjustments can cause significant disruption. Past leap seconds have affected airline check-in systems and taken internet services offline. Experts are also concerned that changes in Earth's rotation could require removing a second for the first time, something many devices did not handle correctly in simulations.

Under the new rules, UTC will run without these one-second jumps. Everyday clocks will not suddenly shift. Instead, the gap between official time and time based on Earth's rotation will be allowed to grow gradually, up to a limit of one hour, which experts expect would take many centuries to reach. Astronomers can continue using measurements of Earth's rotation directly when they need to point telescopes accurately.