The world’s official time standard will stop adding leap seconds from 20 May 2027. The General Conference on Weights and Measures (CGPM) decided to end the practice on Thursday 15 October 2026.
The resolution was adopted at the conference’s 28th meeting in Versailles, where delegates discussed the future of world time.
Until now, leap seconds have been added from time to time to keep atomic time in line with the Earth’s rotation. But from 20 May 2027, Coordinated Universal Time (UTC) will run continuously, with no interruptions.
Why the leap second is being scrapped
The old rules were meant to keep two different ways of measuring time in step. UTC is based on extremely precise atomic clocks. Astronomical time depends on the Earth’s rotation, and that rotation speed varies slightly.
To keep the gap between the two time scales small, 27 leap seconds have been added since 1972. The most recent was at the end of 2016. As a result, one minute could exceptionally last 61 seconds.
These corrections are barely noticeable for people, but they can cause technical problems. Computer systems, telecoms networks, satellite navigation and power infrastructure all depend on precise, reliable time synchronisation. Past leap seconds have already disrupted computer systems and online services.
Earth’s rotation makes new rules necessary
One reason for the decision is the way the Earth’s rotation is evolving. A negative leap second raised new risks.
Over very long periods, tidal forces slow the planet down, but in recent years it has at times been spinning slightly faster.
That raised the possibility that, for the first time, a so-called negative leap second might be needed, with a second removed rather than added. Because this has never been done, it is uncertain how reliably technical systems would cope.
The international expert community therefore chose to end the existing rules ahead of schedule. Under the new regime, the gap between UTC and astronomical time will be allowed to grow, potentially reaching 3,600 seconds, or one hour.
Experts believe, however, that it will still be some time before such a gap would actually require any correction, so the measure is essentially precautionary.
The CGPM: little known, but many member states
The CGPM brings together representatives of member states and of associated states and economic areas and usually meets every four years.
According to the International Bureau of Weights and Measures (BIPM), it currently has 69 member states and 34 associated states and economies.
In Europe, they 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 represented.
What does this mean for the UK?
For everyday life in the United Kingdom, the decision will not bring any immediate change.
Scrapping the leap second is a technical adjustment to the international time reference and must not be confused with the familiar switch between summer time 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.
As such, the local clock time in the UK will still 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 will be unaffected.
A step towards more stable world time
The impact will be felt more strongly in specialist fields that need exceptionally precise alignment with the Earth’s rotation. These include astronomy, geodesy (the science of measuring and mapping the Earth and determining its shape, size and gravitational field) and certain satellite-based applications.
For these disciplines, accurate knowledge of the Earth’s rotation will remain crucial. Because leap seconds will no longer tie world time to that rotation, they will have to account separately for the growing gap between clock time and astronomical time when necessary.
In principle, the aim of the new rules is to make international timekeeping simpler and more reliable in the long term. In particular, digital systems will no longer have to cope with extra seconds being inserted at irregular intervals.