Global timekeepers have voted to make Coordinated Universal Time (UTC) continuous from May 20, 2027, ending leap-second adjustments and allowing it to drift as much as an hour from Earth’s rotation.
The decision was adopted on October 15 by the General Conference on Weights and Measures, which had agreed in 2022 to widen the permitted gap by or before 2035; the new vote brings that change forward. UTC is the international time standard based on atomic clocks, while UT1 tracks Earth’s uneven rotation. Leap seconds were introduced to keep the two close, but the adjustments can create timing glitches in digital systems.
Twenty-seven leap seconds have been added since the practice began, most recently in 2016. Under the new resolution, the permitted difference between UTC and UT1 rises to 3,600 seconds, or one hour. Though often described as a move toward a “leap hour,” the decision does not schedule a one-hour correction; it allows the timescales to drift farther apart and leaves future action for later.
The change aims to avoid disruptions to systems that rely on precise synchronization, including telecommunications, energy and navigation infrastructure. A possible first-ever negative leap second—removing rather than adding a second—also added urgency: a 2025 expert workshop estimated a 30% chance of one being needed by 2035.