In a landmark decision, the General Conference on Weights and Measures (CGPM) voted on 15 October 2026 to abandon the practice of adding leap seconds to Coordinated Universal Time (UTC). The change takes effect on 20 May 2027, ending a system that has been in place since 1972.
The resolution, adopted at the 28th CGPM meeting in Versailles, marks a significant shift in how the world keeps time. Until now, leap seconds were inserted periodically to keep atomic time aligned with the Earth's rotation. From 2027, UTC will run continuously, without these interruptions.
Why the leap second is being scrapped
The old system was designed to reconcile two different ways of measuring time. UTC relies on highly precise atomic clocks, while astronomical time depends on the Earth's rotation, which varies slightly. To keep the difference small, 27 leap seconds have been added since 1972, the most recent at the end of 2016. This occasionally made a minute last 61 seconds.
For most people, these adjustments are imperceptible, but they pose real challenges for modern technology. Computer systems, telecommunications networks, satellite navigation, and power grids all depend on exact time synchronisation. Past leap seconds have already caused glitches in online services and infrastructure.
The decision also responds to the changing behaviour of the Earth's rotation. Over long periods, tidal forces slow the planet, but in recent years it has sometimes spun faster. This raised the possibility of the first-ever negative leap second—removing a second rather than adding one. Because this has never been attempted, experts were uncertain how reliably technical systems would cope.
By ending the practice ahead of schedule, the international community is taking a precautionary approach. Under the new rules, the gap between UTC and astronomical time will be allowed to grow, potentially reaching 3,600 seconds (one hour). However, experts believe it will be many years before any correction is needed.
The CGPM: a global body with European weight
The CGPM brings together representatives from member states and associated economies, meeting roughly every four years. According to the International Bureau of Weights and Measures (BIPM), it currently includes 69 member states and 34 associated states and economies.
European participants include Germany, Austria, France, Italy, Spain, Switzerland, the United Kingdom, Poland, and Ukraine. The Americas are represented by the United States, Canada, Brazil, Argentina, Mexico, and Peru; Asia by China, Japan, India, South Korea, Indonesia, and Thailand; and Africa by South Africa, Egypt, Morocco, Tunisia, and Kenya. Australia and New Zealand are also members.
What does this mean for the UK?
For everyday life in the United Kingdom, the decision brings no immediate change. Scrapping the leap second is a technical adjustment to the international time reference and should not be confused with the familiar switch between summer and winter time.
According to the GOV.UK Clock Change Guide, the clocks go back one hour on Sunday, 25 October 2026, at 2:00 AM. Local time in the UK will continue to follow Greenwich Mean Time (GMT), which is UTC+0 in winter, and British Summer Time (BST), which is UTC+1 in summer. Seasonal time changes remain unaffected.
The impact will be felt more strongly in specialist fields that require precise alignment with the Earth's rotation, such as astronomy, geodesy, and certain satellite-based applications. These disciplines will need to account separately for the growing difference between clock time and astronomical time.
This move is part of a broader effort to make global timekeeping more stable and reliable. As digital systems become ever more interconnected, the risks associated with leap seconds have grown. The decision by the CGPM reflects a consensus among scientists and engineers that a continuous time scale is better suited to the needs of the 21st century.
For Europe, which hosts many of the world's leading timekeeping institutions, the change underscores the continent's role in shaping global standards. The BIPM, based in Sèvres, France, will continue to oversee the implementation of the new rules.
