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Timekeepers want to stop adding leap seconds because the extra timestamp 23:59:60 creates an irregular discontinuity that computer networks, satellite-navigation systems and other critical infrastructure must handle. The proposed replacement would let Coordinated Universal Time (UTC) run continuously while allowing it to drift farther from Earth-rotation time. As of 13 October 2026, that replacement was still awaiting a vote: Draft Resolution C scheduled for 15 October proposes an effective date of 20 May 2027 and a maximum absolute difference between UTC and UT1 of 3,600 seconds (one hour), if governments approve it.
What a leap second does
UTC is the international reference timescale and the basis of civil time in most countries. Its seconds come from atomic standards: UTC is derived from International Atomic Time (TAI). Earth, however, does not rotate at a perfectly uniform rate. UT1 is the timescale determined by that rotation.
Under the current system, leap seconds keep UTC close to UT1. When Earth’s rotation would otherwise push the difference beyond the permitted range, a positive leap second is inserted immediately before midnight. The sequence ends 23:59:59, then 23:59:60, then 00:00:00 on the next day.
NIST’s historical table records 27 positive leap seconds from the first insertion on 30 June 1972 through the latest on 31 December 2016. The current arrangement keeps UT1 and UTC within plus or minus 0.9 seconds. On the NIST page reviewed in 2026, TAI was 37 seconds ahead of UTC.
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Why inserting one second is difficult for computers
A leap second is not simply another second in a clock display. Many software systems assume that each day has a predictable sequence of timestamps and that time moves forward without a repeated or exceptional label. A value such as 23:59:60 can therefore require special code in databases, operating systems, monitoring tools and distributed services.
The BIPM’s 2022 resolution says digital-network and GNSS operators developed different, uncoordinated ways to introduce leap seconds. It identifies risks to critical infrastructure, including global navigation satellite systems, telecommunications and energy transmission. NIST specifically notes that data-logging applications, telecommunications systems and time-distribution services need special attention during an insertion.
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These are risk-management arguments, not a claim that every system fails at every leap second. Operators can test and deploy handling procedures, but the event remains irregular and globally coordinated, while implementations may differ between vendors and networks.
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What would replace leap seconds?
The policy direction approved by the 27th General Conference on Weights and Measures (CGPM) in 2022 is to increase the maximum permitted UT1–UTC difference in or before 2035. That resolution did not set a final limit or an implementation date; it requested a plan and detailed proposal for a later CGPM.
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The BIPM’s 2026 Draft Resolution C supplies those details for a vote at the 28th CGPM. It proposes that UTC continue without leap-second insertions while the absolute UT1–UTC difference is allowed to grow to 3,600 seconds, or one hour. The proposed change would take effect on 20 May 2027 only if the resolution is agreed. The 28th meeting opened on 13 October 2026, and its agenda placed the vote on 15 October, so the change was not adopted at the stated 13 October timestamp.
Continuing leap seconds versus continuous UTC
| Question | Continue leap seconds | Run UTC continuously |
|---|---|---|
| Digital-system behavior | Requires periodic handling of an exceptional timestamp and coordination across systems. | Removes that discontinuity from civil and technical timekeeping, making timestamp sequences more predictable. |
| Relationship to Earth rotation | Keeps UT1 and UTC within ±0.9 seconds under the current procedure. | Permits the difference to increase, with Draft Resolution C proposing a maximum of 3,600 seconds. |
| Astronomy and UT1 users | UTC remains a close proxy for Earth-rotation time for many observations. | Users needing Earth-rotation time must obtain and apply published UT1–UTC information. |
What astronomers and other users would have to change
Ending leap seconds would not change the SI second or the definition of atomic time. It would change how closely civil UTC follows the rotating Earth. Astronomers often use UTC as a convenient reference for observations, and some legacy equipment and software was designed around the existing corrections. NIST warns that those systems and astronomical timestamps could require adjustment if UTC no longer received leap-second corrections.
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The proposed policy does not discard UT1. The 2022 CGPM resolution calls for services that disseminate UT1–UTC to be updated and for users to understand the new, larger possible value. Observatories, satellite operators and other applications that need the Earth’s orientation would continue to use UT1 or a published correction rather than assuming UTC is an accurate substitute.
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Continuous UTC would remove a rare but disruptive event from software and infrastructure schedules. It would also make UTC less directly tied to the planet’s rotation. Keeping leap seconds preserves that link but imposes an exceptional case on systems that otherwise benefit from a uniform atomic timescale.
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The BIPM and NIST describe the issue as a balance between traceability to the SI frequency definition and practical access to Earth-rotation time. The balance has shifted as networked infrastructure has expanded, but neither approach is cost-free: one concentrates complexity in occasional global insertions, while the other shifts responsibility toward UT1–UTC dissemination and the users who need it.
What happens next
- The 28th CGPM considers Draft Resolution C at the scheduled 15 October 2026 vote.
- If approved, the proposed continuous-UTC policy would become effective on 20 May 2027.
- Standards, timing services and affected industries would then need implementation guidance, updated UTC/UT1 dissemination and migration plans for systems that assume leap seconds.
Until a resolution is adopted, the existing rule remains the operative description: leap seconds may be used to keep UT1 and UTC within ±0.9 seconds, and the historical record remains 27 positive insertions through 2016.
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