Why the World Is Scrapping Leap Seconds From 2027

Representatives of the CGPM's 69 member states met at the organisation's 28th General Conference in Versailles, France, and adopted a resolution ending the leap second from 20 May 2027, which is World Metrology Day. The vote was reported by Euronews and confirmed by Scientific American, which quoted Noël Dimarcq, president of the BIPM's Consultative Committee for Time and Frequency, saying "After 30 years of debates, we are ready."

What a leap second actually is

Since 1972, timekeepers have occasionally added a single extra second to UTC, the world's civil time standard, to keep it aligned with UT1, a measure of time based on the Earth's actual rotation. According to Euronews and Scientific American, 27 leap seconds have been added since the system began, most recently at the end of 2016. The adjustment exists because atomic clocks tick at an extremely stable rate, while the planet's rotation speed varies slightly over time.

Why it is being dropped now

Euronews reports that leap seconds have periodically disrupted computer systems and online services; past insertions have been linked to problems at major platforms. The more pressing concern, cited by Euronews, GZT and Scientific American, is that the Earth's rotation has recently sped up at times, raising the possibility that a negative leap second—removing a second rather than adding one—could be required for the first time ever. Because no negative leap second has ever been implemented, Scientific American reports engineers warned this could cause infrastructure disruption similar to the Y2K computer-date problem.

Technology companies have raised concerns about leap seconds for years. The Conversation reports that in 2008, Google avoided a single abrupt one-second adjustment by spreading it gradually across a 20-hour window on its own servers, a technique known as "smearing," and that other companies later adopted similar workarounds.

What changes on 20 May 2027

Under the new rule, UTC will run continuously with no scheduled pauses or insertions. Euronews reports the resolution sets a maximum permissible gap of 3,600 seconds—one hour—between UTC and UT1, rather than the previous limit of under one second. Scientific American and Euronews both report that, at current rates of change, this one-hour gap is not expected to be reached for well over 1,000 years, meaning no timekeeping correction is likely to be needed for centuries.

Who is affected

Euronews and GZT note that the change mainly matters to sectors that depend on precise, uninterrupted time synchronisation: satellite navigation, telecommunications networks, financial trading systems, aviation and power infrastructure. For most people, clocks, phones and everyday scheduling will be unaffected, since the one-second adjustments were never visible in ordinary civil life.

Astronomers, however, lose a convenient link between civil time and the planet's rotation. The Conversation reports that once UTC and UT1 are allowed to diverge for centuries, astronomers can no longer treat UTC as a close proxy for solar time and will need separate methods to track the Earth's actual rotational position.

Background to the decision

The push to end leap seconds is not new. The Conversation and GZT report that a 2022 CGPM decision had initially targeted phasing out leap seconds by 2035, a timeline that was later moved up after concerns grew about the risk of a negative leap second. The October 2026 Versailles resolution finalised a concrete end date of May 2027 for the current system.