World Time Standard Scraps Leap Seconds Beginning in May 2027
Coordinated Universal Time will run continuously without interruptions starting May 20, 2027, eliminating the irregular insertions of time corrections that have historically caused technical failures in computer systems and global infrastructure. Delegates at the 28th meeting of the General Conference on Weights and Measures in Versailles adopted the resolution on October 15, 2026, to permanently alter how international timekeeping manages the variance between atomic clocks and Earth’s rotation.
The decision resolves a decades-long friction point between astronomical time and precise atomic time. Since 1972, international timekeepers have added 27 leap seconds to keep UTC aligned with the planet’s rotation, with the most recent adjustment occurring at the end of 2016. However, unpredictable shifts in Earth’s rotational speed created a new operational threat: the potential need for a negative leap second, which would require removing a second rather than adding one. Because technical systems had never tested the removal of a second, industry standards groups identified severe vulnerabilities that ultimately forced international regulators to scrap the practice entirely.
Technical Failures and the Threat of Negative Leap Seconds
While positive leap seconds have posed synchronization challenges for half a century, the prospect of a negative leap second introduced unprecedented risks to digital architecture. Industry standards groups ran tests that exposed several failures when simulating a negative leap second, according to Patrizia Tavella, time department director at the Bureau International des Poids et Mesures (BIPM), in an email to WIRED. Tidal forces gradually slow the planet over very long periods, but recent years revealed phases where the Earth spun slightly faster, bringing a negative leap second into plausible reality for the first time.
Computer systems, telecommunications networks, satellite navigation platforms, and power grids all depend on uninterrupted, highly reliable time synchronization. Past leap seconds have already disrupted computer systems and online services. By setting the implementation date for May 20, 2027—deliberately chosen to coincide with World Metrology Day and the 1875 signing of the Metre Convention—international regulators aim to remove this recurring vulnerability from digital networks.
Continuous Coordinated Universal Time and Future Timekeeping Adjustments
The permanent removal of leap seconds simplifies operations for system administrators worldwide. Patrizia Tavella noted that time infrastructure managers will have nothing to do except allow normal minutes of 60 seconds to accumulate continuously, eliminating a persistent operational hassle for digital networks. Systems relying strictly on UTC will experience no interruptions or required software patches once the change takes effect.
Yet, letting go of leap seconds means atomic time and astronomical time will gradually drift apart over centuries. To account for this inevitable divergence without burdening digital infrastructure, the BIPM agreed in principle to establish a leap hour in the distant future. Because 3,600 seconds must accumulate before a leap hour becomes necessary, that adjustment remains millennia away. Systems relying instead on astronomical time, known as UT1, will eventually need to utilize future UT1-UTC difference metrics that exceed one second, leaving that computational challenge to future generations.
Frequently Asked Questions About the 2027 Time Standard Change
Why was May 20, 2027, chosen as the implementation date?
The BIPM selected this specific date because it marks World Metrology Day and the anniversary of the signing of the Metre Convention in 1875.
How do seasonal clock changes like daylight saving time factor into this decision?
Seasonal clock changes, such as the UK shifting between Greenwich Mean Time and British Summer Time, remain completely unaffected because the scrapping of the leap second applies solely to Coordinated Universal Time.
What happens to systems that rely on astronomical time rather than atomic time?
Systems relying on UT1 astronomical time will eventually need to process the widening gap between UT1 and UTC, which will grow larger than one second over future centuries.
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