World time faces choice over leap second
International time experts will discuss on Thursday a proposal to continue UTC without leap seconds from 2027.
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The international conference on weights and measures will discuss the future of the leap second in Versailles on Thursday. Delegates will not yet decide on immediate implementation, but on a proposal that would change the system from 20 May 2027.
The 28th General Conference on Weights and Measures, the CGPM, is taking place in Versailles from Tuesday to Thursday. According to the official programme, a session on the future of time measurement, including the relationship between atomic-clock-based UTC and the rotation of the Earth, begins at 09:00 on Thursday.
UTC is based on atomic clocks. Because the Earth does not rotate with complete regularity, an extra second is sometimes added to keep official time close to astronomical time. Such a correction is called a leap second and can cause problems in systems that process timestamps with great precision.
Draft Resolution C proposes widening the maximum difference between UTC and Earth rotation time UT1 to 3,600 seconds, or one hour. This would allow UTC to continue running continuously without future leap seconds. According to the Bureau International des Poids et Mesures, the new method would take effect on 20 May 2027 if the resolution is adopted.
The proposal is primarily intended for digital infrastructure. Telecommunications, energy grids, satellite navigation, financial transactions and other systems benefit from a time scale without an unexpected extra second. The trade-off is that UTC could then diverge further from the actual position of the Sun.
The decision had not yet been taken when this article was published. The BIPM presents the text as a draft, and the official programme refers to discussion and a vote during the conference. The outcome and any wording of the final resolution must therefore be awaited.
Separately, it is already certain that no leap second will be added at the end of December 2026. The United States Naval Observatory published this on the basis of the official announcement by the International Earth Rotation and Reference Systems Service. The discussion in Versailles is therefore mainly about the future time scale, not an extra second at the end of this year.
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The conference, the agenda, the content of Draft Resolution C and the absence of a leap second at the end of 2026 are based on official sources. The text makes no statement about a decision that has not yet been taken.
- confirmed The CGPM will discuss the future of time measurement on 15 October. — This is stated in the official programme for day three. source
- confirmed Draft Resolution C proposes a maximum difference of 3,600 seconds. — The BIPM describes this proposal on its page about the future of UTC. source
- confirmed The proposal would take effect on 20 May 2027 if adopted. — The proposed effective date appears on the BIPM page. source
- confirmed No leap second will be added at the end of December 2026. — The USNO page cites the official announcement. source
Editor's note
The source confirms a discussion and proposed resolution, not the outcome. It therefore clearly states that the decision had not yet been settled at the time of publication.Sources
- Agenda Day 3 — Bureau International des Poids et Mesures
- Future of time metrology — Bureau International des Poids et Mesures
- Leap Second Announcement — United States Naval Observatory
More on this in Dutch media
- NRC — „schrikkelseconde utc”
- NU.nl — „schrikkelseconde utc”
- De Telegraaf — „schrikkelseconde utc”