After three decades of debate within the metrology community, the International Bureau of Weights and Measures (BIPM) confirmed on Thursday that it will cease adding leap seconds to Coordinated Universal Time (UTC) beginning in May 2027. Since their introduction in 1972, a total of 32 leap seconds have been inserted to keep atomic time aligned with the Earth’s rotation.
Why leap seconds were needed
The need for leap seconds arose because the rotation of the Earth is gradually slowing. Tidal friction caused by the Moon, as well as the planet’s molten core, oceans and atmosphere, contribute to a slowdown that creates a growing gap between time kept by atomic clocks and time based on the Earth’s spin, known as Universal Time (UT1). To prevent UTC from drifting too far from UT1, the BIPM periodically adds an extra second, effectively “stretching” the clock to stay in sync. The most recent addition occurred in 2016.
Technical challenges and industry response
While the adjustment maintains astronomical accuracy, it has introduced complications for modern technology that relies on precise timestamps. APIs, databases, and a host of networked systems depend on UTC, and an unexpected extra second can cause errors. Major tech firms such as Google and Meta have adopted a “smear” technique, spreading the extra second over several hours to minimize disruption, according to Judah Levine, a fellow at the U.S. National Institute of Standards and Technology. Nonetheless, incidents have occurred; for example, Qantas experienced a failure in its booking system during a leap second insertion in 2012.
Beyond the operational hassles of positive leap seconds, scientists have warned of a possible negative leap second. A 2024 study in *Nature* suggested that accelerating Earth rotation—partly linked to climate‑induced changes such as melting ice and resulting shifts in planetary gravity—could require the removal of a second as early as 2029. Levine noted that a negative leap second would be more problematic because its effects have never been tested.
Moving beyond leap seconds
Patrizia Tavella, director of BIPM’s time department, cited the growing probability of a negative leap second as a key factor in setting the 2027 cessation date. She referenced tests by an industry standards group that revealed multiple failures when a negative leap second was simulated. The chosen implementation date, May 20 2027, coincides with the anniversary of the 1875 signing of the Metre Convention, which founded the BIPM, and with Metrology Day—a symbolic moment to mark the end of an era.
According to Tavella, the elimination of leap seconds simplifies matters for everyone now: “We have nothing to do—just continue counting normal minutes of 60 seconds.” Levine echoed this sentiment, describing the change as “one less hassle.”
However, the decision does not halt the divergence between atomic and astronomical time. BIPM has indicated that a “leap hour” could eventually be introduced to address the accumulated difference, though such a measure would lie many millennia in the future given the slower rate at which seconds accumulate into an hour. Tavella clarified that while UTC‑based systems will remain unaffected, those that rely on UT1 will need to monitor the growing UT1‑UTC offset, which will eventually exceed one second.
The upcoming discontinuation of leap seconds marks a significant shift in global timekeeping practice, removing a long‑standing source of technical complexity and preemptively avoiding the untested challenges of a negative adjustment.
Mitchell Landsberg is a Senior Technology Correspondent at News Raise. He covers consumer electronics, artificial intelligence, software developments, and digital privacy trends.
