Leap seconds, the one-second adjustments used since 1972 to keep clocks aligned with Earth's rotation, will stop entirely. The world's timekeeping authority, the International Bureau of Weights and Measures (BIPM), confirmed on 15 October 2026 that continuous UTC takes effect on 20 May 2027. The move, first agreed in principle in 2022, was accelerated after experts flagged a growing risk of a disruptive "negative" leap second.
Coordinated Universal Time (UTC), the time standard behind phones, GPS, financial trading and the internet, will stop being nudged by occasional one-second adjustments. According to the official resolution text published by the International Bureau of Weights and Measures (BIPM), 'continuous UTC' becomes effective on 20 May 2027, meaning no new leap second will ever be inserted after that date.
What a leap second is, and why it existed
UTC is built by combining signals from atomic clocks operated by national metrology institutes worldwide, coordinated by the BIPM. Atomic clocks keep extremely steady time, but Earth's rotation is irregular and, on average, gradually slowing, so the length of a solar day drifts away from the atomic-clock second over time, as Wikipedia's entry on the leap second notes.
To stop UTC drifting too far from the Sun-based time scale known as UT1, timekeepers introduced leap seconds in 1972. Whenever the gap between atomic time and Earth's rotation approached 0.9 seconds, an extra second was inserted, usually on 31 December or 30 June. Twenty-seven leap seconds were added between 1972 and the last one, on 31 December 2016, per Wikipedia.
The 2022 vote, and why it was moved up to 2027
In November 2022, the BIPM's member states, meeting as the General Conference on Weights and Measures (CGPM) in Versailles, voted to stop adding leap seconds altogether, setting a deadline of 2035, according to a phys.org report on the vote. The United States and France pushed for the change, while Russia voted against the timeline, preferring 2040 so its GLONASS satellite navigation system would have more time to adapt, Al Jazeera reported.
The 2035 target did not survive unchanged. At the 28th CGPM in Versailles on 15 October 2026, member states adopted Resolution 5, pulling the deadline forward to 20 May 2027. The resolution itself explains why: a BIPM-organized workshop estimated roughly a 30% probability of needing a never-before-used 'negative' leap second by 2035, a scenario the resolution says poses a high risk of disruption to critical infrastructure that is largely unprepared for it.
The resolution also raises, rather than just removes, the tolerance for drift: the maximum allowed gap between UT1 and UTC rises from 0.9 seconds to 3,600 seconds (one hour). The BIPM says this single change keeps UTC continuous for several centuries before any correction would even need to be discussed.
Why the change: real outages, not just annoyance
Leap seconds have caused documented technical failures. Al Jazeera's reporting cites 2012 incidents in which the leap-second insertion contributed to crashes affecting LinkedIn, Reddit and Qantas's booking systems. Engineers at Meta have described leap seconds as a significant source of difficulty for teams that manage hardware infrastructure, according to the same report.
The BIPM's resolution adds that the expanding use of the Internet of Things, smart grids and other distributed systems increases the risk that a single leap second, inserted unevenly across global networks, could cause malfunctions. It also warns that continued delay risked industries abandoning UTC altogether in favor of satellite-navigation time scales such as GNSS time, undermining a single global reference for time.
What NIST and scientists have said
Judah Levine, a physicist at the US National Institute of Standards and Technology, told reporters after the 2022 vote that the gap between atomic and astronomical time would eventually need handling through a 'smear,' spreading a larger correction, potentially a future 'leap minute,' over an extended period rather than an abrupt jump, according to phys.org.
Leap-second system vs. continuous UTC
Aspect
1972–2016 system
From 20 May 2027
Maximum UT1–UTC gap allowed
0.9 seconds
3,600 seconds (1 hour)
Adjustments made
27 leap seconds inserted; last on 31 Dec 2016
None; no leap second will be inserted again
Decided by
BIPM/IERS, announced a few months ahead each time
CGPM Resolution 5 (2026), date fixed in advance
Next scheduled review
Irregular, unpredictable
Not expected for several centuries, per BIPM
What it means for technology and astronomy
For most people, the change is invisible: clocks, phones and calendars will not look or behave differently. For engineers, it removes a recurring source of software bugs tied to the irregular, short-notice insertion of an extra second into timestamp systems, the kind of event Al Jazeera's report links to the 2012 outages.
For astronomy and geodesy, the BIPM resolution notes that UTC will now diverge slowly but steadily from Earth's actual rotational position, UT1. Wikipedia's entry notes that if no correction is ever made, solar noon and civil clock time would eventually drift apart, though the BIPM's one-hour tolerance means that divergence will take centuries to become significant. The BIPM says it will keep working with the International Telecommunication Union, the International Astronomical Union, the International Union of Geodesy and Geophysics, and the International Earth Rotation and Reference Systems Service to track the UT1-UTC gap over time.
A 30% probability by 2035 of a negative leap second... poses a high risk of causing anomalies and disruption to critical infrastructures that are largely unprepared.
— Resolution 5 of the 28th CGPM (2026), BIPM
Questions
What exactly is a leap second?
It is a one-second adjustment occasionally added to Coordinated Universal Time (UTC) to keep atomic-clock time aligned with Earth's slightly irregular rotation. Leap seconds were used from 1972 to 2016, with 27 inserted in total, according to Wikipedia.
When do leap seconds officially end?
Continuous UTC, with no further leap seconds, becomes effective on 20 May 2027, under Resolution 5 adopted by the 28th General Conference on Weights and Measures (CGPM) on 15 October 2026, according to the BIPM.
Why was the original 2035 deadline moved up?
The BIPM's resolution cites a roughly 30% estimated probability of needing an unprecedented 'negative' leap second by 2035, which it says would risk serious disruption to infrastructure that is largely unprepared for it.
Will I notice any difference in my phone or computer clock?
No. The change mainly affects how timekeeping systems are engineered; everyday displayed time will not visibly change, though it removes a known source of software failures tied to leap-second insertions, as reported by Al Jazeera.
What happens to the gap between clock time and Earth's rotation now?
The allowed difference between UT1 (Earth-rotation time) and UTC rises from 0.9 seconds to 3,600 seconds (one hour), a tolerance the BIPM says will keep UTC continuous for several centuries before any correction needs to be considered.
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A leap second is a one-second correction added to Coordinated Universal Time (UTC) to keep it within 0.9 seconds of Earth's actual rotation. On 15 October 2026 the General Conference on Weights and Measures (CGPM) voted to stop inserting leap seconds from 20 May 2027, letting UTC drift from Earth's rotation by up to one hour instead of one second.
