The Leap Second's Days Are Numbered as Global Timekeepers Weigh a Century-Scale Fix

A 54-Year Timekeeping Tradition Is on the Chopping Block

Earth's increasingly quirky spin may soon trigger a small but consequential makeover for the world's clocks. International timekeepers are weighing a plan to scrap the occasional "leap second" and instead allow time to drift until a full leap hour is needed — likely centuries from now. It sounds like science fiction, but it's a very real proposal moving toward a formal vote this fall.

International timekeeping authorities are preparing to vote on a proposal to make the leap second — an extra second that is occasionally added to the year to keep Coordinated Universal Time (UTC) in tune with Earth's rotation — into a leap hour as early as 2027. The leap second was introduced in 1972 by the International Bureau of Weights and Measures (BIPM) to match UTC with Earth's gradually slowing spin. Every time UTC becomes one second too fast for Earth, timekeepers add a leap second to UTC. Since then, international bodies have added 27 leap seconds to UTC to keep atomic clocks within 0.9 seconds of Earth's wobbly rotational time.

Why the Old System Is Breaking Down

Leap seconds, in use since 1972 to keep Coordinated Universal Time in sync with Earth's rotation, have long vexed computers, contributing to outages at companies including Meta and Reddit and complicating high-speed trading and aviation systems. In other words, what seems like a minor bureaucratic tweak to the clock has real-world consequences every time it happens.

With Earth now spinning slightly faster, a never-before-used "negative leap second" could be required before 2035 — a scenario that experts warn could be even more disruptive. Setnam Shemar, principal scientist at the UK's National Physical Laboratory, pointed out that network time servers and digital frameworks are predominantly built with hardcoded assumptions that leap seconds always increase time. Shemar elaborated that removing a second might provoke widespread and intense instability throughout vital national systems, such as satellite navigation networks, electrical grids, and telecommunications.

Recent measurements show an increase in Earth's rotational speed, pushing experts to estimate a 30 percent probability that a negative leap second will be required by 2035. That's not a risk the world's timekeepers are willing to gamble on.

What a "Leap Hour" Actually Means

Member states of the General Conference on Weights and Measures (CGPM) will vote on the resolution at their 28th meeting, outside Paris on October 13–15. If it passes, the plan could go into effect as early as 2027. Under the new framework, UTC would be allowed to drift from Earth's rotational time by up to one full hour before any correction was required. At Earth's current rate of rotation variation, that threshold would take 50 to 100 years to reach — effectively removing the leap second problem from the engineering agenda for the foreseeable future.

Adopting a leap hour approach shifts the burden of time correction from automated, split-second code fixes to scheduled maintenance windows — a far more manageable proposition for the global technology infrastructure. Patrizia Tavella, director of the Time Department at the BIPM, says there is sufficient urgency to put the leap hour into effect as soon as possible.

What Comes Next

Every four years, the General Conference on Weights and Measures brings together timekeeping authorities from around the world to discuss efforts to maintain UTC and its associated standards. In 2022, the 64 member states agreed to find a way to extend the allowed difference between UTC and Earth's position from one second to a higher time limit by 2035. The October vote is the next major step in fulfilling that commitment.

If passed, the new framework removes the need for leap-second adjustments for at least a thousand years, shielding enterprise infrastructure from timing anomalies. For most people, the change will be invisible — your phone won't suddenly jump an hour. But behind the scenes, it would represent one of the most significant overhauls to global timekeeping in over half a century, quietly future-proofing the digital systems that modern life depends on.