International Experts Vote to Eliminate Leap Seconds Starting in 2027

International metrology experts meeting in Versailles have voted to eliminate the leap second starting on May 20, 2027. The historic decision, formalized through Resolution 5 at the General Conference on Weights and Measures (BIPM), aims to ensure that Coordinated Universal Time (UTC) runs continuously without the sudden adjustments that have historically complicated digital infrastructure.

For decades, official timekeeping relied on adding occasional leap seconds to bridge the gap between atomic clocks, which tick with absolute precision, and the Earth's rotation, which fluctuates unpredictably. Since 1972, the international community has inserted 27 leap seconds. However, because the Earth's rotation has recently accelerated, scientists faced the unprecedented prospect of implementing a negative leap second, which would require subtracting a full second from global time.

Researchers warned that a negative leap second posed severe, unquantified risks to critical digital systems. Computer networks, telecommunications, financial markets, power grids, and flight reservation systems rely heavily on precise, uninterrupted timestamps. When a standard leap second occurs, it creates a duplicate timestamp value of 23:59:59 that frequently trips up software routines. Deleting a second entirely was projected to introduce even higher risks of severe technical anomalies.

Under the newly adopted framework, the allowable discrepancy between atomic time and astronomical rotation will expand significantly from 0.9 seconds to a full 3,600 seconds, or one hour. According to scientific estimates, it will take more than 3,000 years for the Earth's rotation to drift enough to reach this new one-hour ceiling. This wide margin effectively abolishes the need for leap seconds for multiple centuries.

While the shift to a continuous global time standard is critical for engineers and astronomers, everyday citizens will not notice any changes in their daily lives. Smartphones, computers, and standard wristwatches will continue to operate normally without sudden time shifts. Furthermore, the decision has no impact on seasonal daylight saving time changes, which remain governed by separate regional and national legislation.

In addition to phasing out the leap second, the conference addressed future technological needs by planning a redefinition of the second by 2030 to accommodate advanced optical atomic clocks. Delegates also voted to begin developing an independent lunar timescale to support upcoming space exploration and infrastructure projects on the Moon, where gravitational differences alter how standard Earth clocks tick.