Tech and AI
The world's timekeepers move to abolish the leap second from May 2027
By Staff Writer | 7 September 2026
A draft resolution before the General Conference on Weights and Measures next month would let civil time drift from the Earth's rotation by up to an hour. The reason is a correction that has never been attempted and that critical infrastructure is not built to survive.
The General Conference on Weights and Measures, the intergovernmental body that owns the International System of Units, meets for its 28th session from 13 to 15 October 2026. Among the draft resolutions published for the meeting is Draft Resolution C, on the technical actions needed to ensure the continuity of UTC. If the national delegates adopt it, Coordinated Universal Time becomes a continuous time scale from 20 May 2027, and the leap second is finished.
What the leap second does
UTC is kept by atomic clocks and runs at the same rate as International Atomic Time. The Earth does not. Its rotation wobbles and, over the long run, slows, so a day measured by the planet is not exactly 86,400 atomic seconds. Since 1972 the difference has been held within 0.9 seconds by inserting a leap second whenever the two drift apart, and 27 have been inserted. Every one of them has added a second. None has ever taken one away.
That is now the problem. The Earth's rotation has quickened slightly in recent years, and a workshop convened in March 2025 by the Consultative Committee for Time and Frequency and the International Earth Rotation and Reference Systems Service, including specialists in Earth rotation, estimated that the probability of a negative leap second being required would rise quickly, reaching 30 per cent by 2035.
Most digital architectures and network time servers are hardcoded under the assumption that leap seconds are strictly additive. Losing a second could trigger severe disruption across critical national infrastructure, including telecommunications, electricity grids, and satellite navigation systems
Setnam Shemar, principal scientist at the National Physical Laboratory
What the resolution says
The draft is unusually direct for a metrology document. It records that a negative leap second has never been applied and is considered to pose a high risk of anomalies and disruption to critical infrastructures that are largely unprepared, and that preparing for one would require the industries that depend on time synchronisation to make a financial investment estimated to be similar to their preparations for the millennium bug. It notes that the spread of connected devices, dispersed sensor systems and smart grids raises the risk of malfunction from any leap second, and that the different smoothing methods global service providers already use to avoid a time step have left different systems disagreeing with each other about what time it is.
It also records a risk to the standards system itself. If the change is delayed, some organisations may abandon UTC as their reference and take their time from a satellite navigation constellation instead, which the resolution describes as seriously compromising the concept of international standardisation in metrology.
The decision proposed: continuous UTC from 20 May 2027, and a maximum permitted difference between UTC and the Earth rotation time scale UT1 of 3,600 seconds, one hour, which the resolution says secures the continuity of UTC for several centuries.
The groundwork was laid in 2022, when the 27th General Conference decided the tolerance would be widened by 2035 at the latest and asked for a resolution to be drafted for this meeting. The 2023 World Radiocommunication Conference endorsed that decision and allowed radio time signals a transition period to 2035, and no later than 2040, where equipment cannot be replaced sooner. The remaining question was only the date, and the draft brings it forward to 2027.
This would remove the risks entirely for a very long time. Next month's resolution is likely to pass since it will be based on the outcome of a majority vote of the national delegates from many different countries, and most of them have been keen to end leap seconds for several years due to the risks posed to national infrastructure.
Setnam Shemar, principal scientist at the National Physical Laboratory
What it means on site
Nobody on a construction project will notice an hour's drift between the clock and the sun, because that will take well over a thousand years to accumulate. What the change removes is a hidden fault line under every system that stamps a time on a record: building management systems, access control, site cameras, electronic tendering portals, the payment platforms that decide whether a notice was served in time. Each of them takes its time from a server that takes it from UTC, and each was written by someone who assumed a minute always has at least sixty seconds. The resolution is a decision to stop testing that assumption.