Continuous UTC from 20 May 2027: the new timekeeping decisions
The CGPM has set a date for eliminating leap-second discontinuities and adopted recommendations on lunar time. This is not a change of time zone.
The 28th General Conference on Weights and Measures (CGPM) adopted two different steps on 15 October 2026 in Versailles: a specific timetable for continuous UTC on Earth and recommendations for a common approach to lunar time.
The date that was decided
Resolution 5 sets 20 May 2027 as the date when continuous Coordinated Universal Time (UTC) takes effect. The aim is to eliminate leap-second discontinuities. This is a future date; the transition has not already happened.
The maximum permitted difference between UTC and UT1, which is linked to Earth’s rotation, is set at 3,600 seconds. This is a limit on divergence, not an instruction to move clocks by one hour. The decision does not abolish daylight-saving time or change Greece’s time zone.
Why digital infrastructure is affected
The Consultative Committee for Time and Frequency (CCTF) explains that leap-second adjustments complicate continuous synchronization in transport, energy and telecommunications. The possibility of a first negative leap second is a particular concern. This concerns technical infrastructure planning, not an instruction for individuals to change their clocks manually.
What was decided for the Moon
Resolution 6 calls for sharing experience from pioneering lunar projects, clearly describing relativistic models and uncertainties when comparing time with UTC. The aim is interoperable positioning, navigation and timing systems. It does not announce an already operational worldwide network of lunar clocks.
A separate resolution prepares a possible new definition of the second for consideration in 2030, according to the CCTF. This does not mean that the unit has already changed.
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