The decision calendar
Every dated commitment in the international time standards record, and the document that sets it.
Decisions about time are made slowly and announced quietly, usually in a draft document that is amended several times before anyone outside the committee reads it. This page lists the dates currently on the record, what happens on each, and which document to check. Each entry has its own address, so a single date can be linked to directly.
Dates here are only those stated in a published document. Where a document has been superseded, the superseded date is noted rather than deleted.
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The United States directs a lunar time standard
A policy memorandum from the Office of Science and Technology Policy, Celestial Time Standardization in Cislunar Space, directed NASA — coordinating with the Departments of Commerce, Defense, State and Transportation — to deliver a finalized lunar time standardization strategy. It set the deadline recorded below at 31 December 2026.
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The end of the leap second acquires a date
Version 2 of the draft resolutions for the 28th CGPM recorded a single change: “Draft Resolution C: effective date of continuous UTC set on 20 May 2027.” Until that revision the governing figure was 2035, from Resolution 4 of the 2022 Conference. The change was made in a version history line and was not separately announced.
BIPM, Draft Resolutions of the 28th CGPM, version history
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Revised frequency values take effect
The re-adjusted CIPM list of recommended values of standard frequencies became active, having been approved by the Consultative Committee for Time and Frequency in September 2025. The adjustment moved several recommended values, added two candidate species, and applied a random-effect uncertainty to the whole body of input ratios.
BIPM, recommended values of standard frequencies (CCTF Recommendation 24-2)
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The text that goes to the vote
Version 5 of the draft resolutions was published. This is the current text of Draft Resolutions B, C and D. Earlier revisions changed substance: Version 4, of 30 June 2026, refined Draft Resolution D to specify a single lunar reference time scale with multiple possible realizations. Drafts remain amendable up to and during the Conference.
BIPM, Draft Resolutions of the 28th CGPM, Version 5
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The 28th General Conference on Weights and Measures
Meeting at the Palais des Congrès in Versailles. Three of the resolutions before it concern time. Draft Resolution C ends the leap second. Draft Resolution D addresses lunar time. Draft Resolution B declines to propose a new definition of the second and asks for one by 2030.
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NASA’s lunar time strategy is due
The deliverable set by the 2024 OSTP policy. As of the date of this page it has not been published. Note that the international definition adopted by the International Astronomical Union in 2024 is TCL, within the LCRS reference system — not “LTC”, the name widely reported at the time.
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Continuous UTC takes effect
If Draft Resolution C is adopted, no further leap seconds are inserted after this date. The maximum permitted value of |UT1−UTC| rises to 3,600 seconds — one hour — which the resolution states will ensure continuity “for several centuries.” Civil time is thereafter permitted to drift from the rotation of the Earth without correction.
This leaves roughly seven months between adoption and effect for every system that encodes UT1−UTC in a fixed field: GNSS broadcast messages, time dissemination services, and PTP and NTP infrastructure.
Draft Resolution C · CCTF report on Draft Resolution C · Sothic brief: Three Votes on Time
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The second is redefined, or postponed
Draft Resolution B asks the CIPM to continue work so that a proposal for a new, optical definition of the second can be presented at the 29th Conference, together with a date of implementation. The CCTF strategy document is explicit that this is “a decisive milestone, either to approve the new definition or to postpone it to the 30th CGPM in 2034.” The slip path is designed in: 2030 is a decision point, not a deadline.
Draft Resolution B · CCTF Strategy 2025–2035 · Sothic brief: The Clocks Do Not Agree
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The designed fallback
Named in the CCTF strategy as the alternative venue for adopting a new definition of the second if the 2030 decision is to postpone. A slip to 2034 would be the plan operating as written, not its failure.
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Legacy UT1−UTC broadcasting ends
ITU Resolution 655 (Rev. WRC-23) permits the legacy terrestrial time code carrying UT1−UTC until 2035, and no later than 2040. A 2025 CCTF survey found five countries still broadcasting it: Argentina, Canada, Russia, the United Kingdom and the United States.
2035 is also the year named in CGPM Resolution 4 (2022) as the outer bound for increasing the UT1−UTC tolerance. That figure was widely reported and is now superseded by 20 May 2027.
ITU Resolution 655 (Rev. WRC-23) · CGPM Resolution 4 (2022)
Standing of this page
Maintained and dated. Last reviewed 20 September 2026. Where a date changes, the change is logged at sothic.org/corrections and the entry here is amended rather than replaced.
If a dated commitment is missing from this list, editor@sothic.org.