Timekeepers want to stop adding leap seconds because the adjustment can create a discontinuity that digital systems handle in inconsistent ways. The trade-off is that civil UTC would no longer stay as close to Earth’s rotation: astronomers and other users needing rotation-based time would rely more on published UT1–UTC corrections. As of 13 October 2026, a proposal to make UTC continuous was still awaiting a scheduled vote.
What a leap second does
UTC is the international reference time used as the basis for civil time in most countries. It is derived from International Atomic Time (TAI), whose seconds follow the SI definition based on atomic frequency. Earth’s rotation, by contrast, is not perfectly uniform. UT1 is a time scale tied to that rotation.
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Leap seconds have been used to keep UTC close to UT1. Under the current arrangement described by NIST, the difference is kept within ±0.9 seconds. When a positive leap second is inserted, the clock can show 23:59:60 before advancing to 00:00:00. NIST’s historical table records 27 positive insertions, from the first on 30 June 1972 through the latest on 31 December 2016. The SI second itself does not change; the extra label reconciles civil time with Earth-rotation time.
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1Clear out junk files and repair common Windows errors2Scan for outdated or missing drivers - takes under a minute3Repair Windows errors before they cause bigger problemsNIST’s page reviewed for this article says TAI is 37 seconds ahead of UTC. That accumulated offset reflects leap seconds applied over time; it is distinct from the sub-second UTC–UT1 difference the current system aims to maintain.
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Why timekeepers want to stop inserting them
The central concern is not that every computer fails when a leap second occurs. It is that the adjustment creates an irregular event, and operators have implemented it in different, uncoordinated ways. The 27th General Conference on Weights and Measures (CGPM) said in its 2022 resolution that this inconsistency poses risks to critical digital infrastructure, including global navigation satellite systems (GNSS), telecommunications and energy transmission.
NIST also identifies data-logging applications, telecommunications systems and time-distribution services as systems that need special attention during leap seconds. For systems that assume time advances predictably, an unusual second can require special handling. Different implementations complicate coordination across networks and services that depend on consistent timestamps.
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The standards bodies’ case is therefore about reducing one source of discontinuity and operational complexity—not a claim that leap seconds inevitably cause outages, or that every affected system behaves the same way. NIST researchers Judah Levine and Patrizia Tavella wrote in 2024 that the balance between linking UTC to the SI frequency definition and keeping it close to UT1 had changed, and discussed increasing the permitted separation while retaining a link.
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What would change—and what would not
If leap seconds stop, UTC could progress continuously without inserting the occasional 23:59:60. The benefit is a more predictable civil time scale for systems that must handle timestamps. The cost is that UTC could drift farther from Earth-rotation time, so it would no longer serve as a near-immediate proxy for UT1.
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This would not change the length of the SI second or make Earth rotate differently. It would change how closely the civil reference time is required to track that rotation. UT1 would still matter, and the BIPM’s 2022 resolution calls for services disseminating UT1–UTC information to be updated, with users informed about the larger permitted difference.
Who would need to adapt
A close UTC–UT1 relationship lets astronomers use UTC for many observational purposes. If that relationship becomes looser, astronomy and other work that depends on Earth’s orientation would need to use UT1–UTC correction information more directly. NIST also warns that astronomical timestamps and legacy equipment or software synchronized to UTC could require adjustment. The practical change is a shift in which time scale users consult, not the disappearance of Earth-rotation data.
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How the two approaches compare
| Approach | Digital-system continuity | Relationship to Earth’s rotation | Adjustment burden |
|---|---|---|---|
| Continue leap seconds | Requires systems to handle occasional discontinuities; operators have used differing introduction methods. | Under the current arrangement described by NIST, UTC and UT1 are kept within ±0.9 seconds. | Time-sensitive systems need leap-second handling; users can rely on UTC staying close to UT1. |
| Allow continuous UTC with a larger UT1–UTC difference | Avoids leap-second insertions, reducing one source of irregularity in technical timekeeping. | The 2026 draft proposed allowing an absolute difference of up to 3,600 seconds (one hour). | Users needing Earth-rotation time would rely more directly on UT1–UTC information; some astronomical timestamps and legacy systems may need adjustment. |
What has been decided, and what was still pending
In 2022, the 27th CGPM adopted Resolution 4, deciding that the maximum difference between UT1 and UTC should be increased in or before 2035. It also requested a plan and detailed proposal for the next CGPM meeting. That decision did not set the final one-hour limit or a 2027 start date.
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In 2026, the BIPM published Draft Resolution C proposing a maximum absolute UT1–UTC difference of 3,600 seconds, or one hour, with an effective date of 20 May 2027 if the resolution were agreed. The 28th CGPM meeting opened on 13 October 2026, and its agenda scheduled the vote on Draft Resolution C for 15 October. As of 13 October, the detailed proposal had not been adopted; the proposed date and limit remained conditional.
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Sources and further detail
- BIPM: Coordinated Universal Time (UTC), on how UTC is derived from TAI and related to Earth’s rotation.
- NIST: Leap Seconds, with the insertion history and practical effects.
- 27th CGPM Resolution 4 (2022), on the decision to increase the allowed UT1–UTC difference and its stated infrastructure risks.
- BIPM: Future of metrology, describing Draft Resolution C and its proposed limit and effective date.
- 28th CGPM meeting, including the meeting agenda and scheduled vote.
- NIST: 2024 paper record on redefining UTC, by Judah Levine and Patrizia Tavella.
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