Overview
- Member states of the General Conference on Weights and Measures voted on Thursday, Oct. 15, 2026 to end the practice of inserting leap seconds and to adopt a ‘leap hour’ policy that takes effect on May 20, 2027.
- Under the new rule Coordinated Universal Time (UTC) may diverge from astronomical time (UT1) by as much as 3,600 seconds before an adjustment is applied.
- The change was driven by repeated technical outages and operational complexity tied to leap seconds, with technology firms and engineers warning a rare ‘negative leap second’ could cause severe software failures.
- International services will continue to monitor and publish UT1 so astronomers, celestial navigators and other specialists can correct observations and systems that need Earth-rotation time.
- Metrologists say a leap hour correction is unlikely to be needed for many centuries, which preserves continuous atomic time now but defers synchronization decisions to future generations.