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Leap Seconds End in 2027: How the New UTC Rule Works
From May 20, 2027, UTC will run without leap seconds, and its permitted difference from Earth rotation time will rise to 3,600 seconds—one hour. Leap seconds have been used since 1972 to keep UTC close to Earth’s rotation; the last was added on December 31, 2016.
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Key takeaways
- From May 20, 2027, UTC will run without leap seconds, and its permitted difference from Earth rotation time will rise to 3,600 seconds—one hour.
- Leap seconds have been used since 1972 to keep UTC close to Earth’s rotation; the last was added on December 31, 2016.
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openai.comCreate a landscape editorial hero image for this Studio Global article: What did delegates at the General Conference on Weights and Measures in Versailles decide on October 15, 2026, about ending leap seconds on. Article summary: Delegates meeting in Versailles on October 15, 2026, decided to end leap-second adjustments and make UTC continuous from May 20, 2027, bringing forward the 2035 endpoint agreed in 2022. [6][7][5] The available evidence c. Topic tags: general, general web, government, academic, news. Style: premium digital editorial illustration, source-backed research mood, clean composition, high detail, modern web publication hero. Use reference image context only for broad subject, composition, and topical grounding; do not copy the exact image. Avoid: logos, brand marks, copyrighted characters, real person likenesses, fake screenshots, UI text, readable text, watermarks, cha
Timekeepers have approved a major change to the world’s civil time standard: from May 20, 2027, Coordinated Universal Time (UTC) will run continuously, without leap-second adjustments. The change replaces the 2035 target set in 2022 with a new limit: UTC and Earth-rotation time may differ by as much as 3,600 seconds, or one hour. 4
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What changed—and when
At its October 2026 meeting in Versailles, the General Conference on Weights and Measures approved the change to continuous UTC, effective May 20, 2027. Reporting says representatives from 69 countries voted; the source material available here does not provide a full vote tally. 21
The decision advances the earlier plan to stop leap-second adjustments by 2035. Until the new rule takes effect, leap seconds remain the way timekeepers occasionally adjust UTC to stay close to the time scale based on Earth’s rotation. 4
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The last leap second was added on December 31, 2016. 7
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Why UTC is being allowed to drift
Atomic clocks provide a steady measure of time, while Earth’s rotation is not perfectly regular. UT1 is the time scale based on that rotation. Leap seconds have been used since 1972 to keep UTC close to UT1; under the new rule, that close alignment is no longer required. 7
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The wider gap is intended to avoid making small, irregular changes to official time. One concern behind the proposed change was the possibility of a negative leap second—a one-second subtraction rather than an addition. Such an adjustment had never been used, and reporting described it as a potential complication for timekeeping systems. 19
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Is a “leap hour” actually planned?
The phrase “leap hour” describes the new one-hour allowance, but it can give the wrong impression. The decision sets a maximum permitted difference of 3,600 seconds between UTC and UT1; it does not specify a date for adding or subtracting an hour. 2
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So the change does not mean clocks will suddenly jump by an hour in 2027. It means UTC can continue without leap seconds while the difference from Earth-rotation time grows within the new limit. The material available here does not establish when that limit might be reached or how any later correction would be made.
Other timekeeping work at the conference
Leap seconds were not the only timekeeping subject on the conference agenda. The BIPM’s list of adopted resolutions includes a separate resolution on an international lunar reference time scale and its traceability to UTC. 37
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A statement from the committee responsible for time and frequency standards also notes that optical frequency standards have surpassed the best realizations of the current second definition, while some criteria for a future definition remain unmet. That work is related to the wider development of time standards, not a correction mechanism for the leap-second change. 39
The practical takeaway is straightforward: from May 20, 2027, UTC will no longer receive leap seconds, and its permitted separation from Earth-rotation time will expand to one hour. The “leap hour” is a label for that larger tolerance—not a scheduled hour-long adjustment. 2
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What is the short answer to "Leap Seconds End in 2027: How the New UTC Rule Works"?
From May 20, 2027, UTC will run without leap seconds, and its permitted difference from Earth rotation time will rise to 3,600 seconds—one hour.
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From May 20, 2027, UTC will run without leap seconds, and its permitted difference from Earth rotation time will rise to 3,600 seconds—one hour. Leap seconds have been used since 1972 to keep UTC close to Earth’s rotation; the last was added on December 31, 2016.
Sources
trustlist.ukLeap seconds end as UTC becomes continuous on 20 May 2027
indexbox.ioLeap Seconds to End in 2027: CGPM Votes to Stop Adding Them to UTC - News and Statistics - IndexBox
realsize.worldThe end of the leap second: what was decided and what the ...
newscientist.comScientists have just voted to abolish leap seconds