Timekeepers vote to retire leap seconds
The new system will allow civil time to drift by up to an hour from Earth’s rotation before any future adjustment is considered.
The world’s timekeeping authorities have voted to move towards a continuous global time scale, ending the need for regular leap seconds. The change will not add an hour to clocks now; it will widen the tolerance between atomic time and the Earth’s rotation.
The decision was taken on Thursday at the General Conference on Weights and Measures, the international body responsible for agreements on measurement standards. The UK’s National Physical Laboratory said the vote would avoid the need for leap seconds in future and that the new approach would begin on 20 May 2027.
Leap seconds have been used since 1972 to keep Coordinated Universal Time, or UTC, close to UT1, a time scale based on the Earth’s rotation. Atomic clocks provide the steady reference for UTC, while the planet’s rotation varies because of natural processes and is not perfectly regular.
Under the present system, UTC must remain within roughly one second of UT1. The new rule will allow the difference to grow to as much as 3,600 seconds. That is why the proposal has sometimes been described as replacing a leap second with a leap hour, although no one-hour adjustment is scheduled now.
The timetable was brought forward because Earth has been rotating unusually quickly in recent years. The National Physical Laboratory says current estimates put the probability of a first negative leap second, in which a second would be skipped rather than added, at about 30% within the next decade. Such an adjustment has never been carried out.
The main concern is technical rather than visible to the public. Leap seconds are irregular and can conflict with software that assumes time always moves forward in equal one-minute increments. The NPL says incorrect implementation can create discrepancies between networks and affect systems such as mobile communications and electricity grids.
UTC will remain the common international reference, and the link with Earth’s rotation will not disappear. UT1 will continue to be measured and published for uses including astronomy and celestial navigation. The eventual size of any future adjustment will depend on the unpredictable speed of Earth’s rotation, while its timing is expected to be many centuries away.
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The article is based on a UK primary source and two independent public explanations of the decision. It clearly separates the confirmed rule change from the distant possibility of a future leap hour.
- confirmed The CGPM voted on 15 October 2026 to move towards a continuous global time scale. — Confirmed by the National Physical Laboratory’s announcement published on the same day. source
- confirmed Leap seconds have been used since 1972 to keep UTC aligned with Earth’s rotation. — Explained by the NPL and ABC News. source
- confirmed The new system will allow a UTC–UT1 difference of up to one hour from 20 May 2027. — The implementation date and one-hour tolerance are stated by the NPL. source
- confirmed The NPL estimates about a 30% probability of a negative leap second within the next decade. — The probability appears in the NPL announcement and is also reported by Time and Date. source
- confirmed A negative leap second has never been implemented. — Confirmed by ABC News and Time and Date. source
- confirmed UT1 will continue to be measured and disseminated for applications such as astronomy and celestial navigation. — Stated explicitly by the National Physical Laboratory. source
Editor's note
The vote and the 20 May 2027 implementation date are confirmed by the National Physical Laboratory and Time and Date. ‘Leap hour’ is shorthand for the permitted future difference between UTC and UT1, not an imminent one-hour change to civil clocks.Sources
- The future of timekeeping — National Physical Laboratory
- The World Abandons Leap Seconds — Time and Date
- World’s timekeepers to vote on ditching leap second — ABC News
More on this in other media
- Sky News — „timekeeping leap second”
- BBC News — „timekeeping leap second”
- The Guardian — „timekeeping leap second”