The world’s timekeepers have retired the leap second. On October 15, 2026, the Conférence Générale des Poids et Mesures (CGPM) voted to abolish the practice of adding an extra second to atomic clocks to keep them in sync with Earth’s rotation, a decision driven by the operational chaos these time adjustments cause for global digital infrastructure.
The era of the leap second is over. The decision came from the CGPM, a body representing over 100 nations, who voted near-unanimously to scrap the system that has defined our coordinated time.
The Two Clocks That Couldn’t Agree
To understand why the leap second had to go, you first need to grasp the fundamental conflict at the heart of timekeeping. We live with two competing definitions of a second. The older one, UT1, is astronomical.
It’s based on the rotation of the Earth, the planet’s spin on its axis in 24 hours. This is the time you’d use for celestial navigation, the time of Greenwich Mean Time (GMT), defined by the sun’s passage over the meridian.
The second, and far more precise, definition is the atomic second. Adopted by the CGPM in 1967, this standard is based on the hyper-stable oscillation of the cesium-133 atom. Its radiation oscillates like a pendulum at a remarkably stable rhythm, forming the basis of Coordinated Universal Time (UTC).
This is the time that governs our satellites, financial transactions, and the internet’s packet routing. The problem is simple: the Earth is a messy, inconsistent timekeeper. Its rotation is much more irregular. Atomic clocks, however, are ruthlessly precise.
Leap Seconds Introduce Failure Points into Digital Systems
In 1972, to bridge this gap, the leap second was born. The idea was to insert an extra second into UTC at irregular intervals—usually on June 30 or December 31—to maintain a minimum difference of less than one second between UT1 and UTC. For 27 leap seconds added since 1972, this patchwork system worked. But it introduced a point of failure into our most critical digital systems.
A leap second is not a clean, predictable event. The fact of adding time from time to time, in general on June 30 or December 31 of certain years, one or several leap seconds to atomic clocks greatly disturbs the computer systems on which we depend. In 2012 and 2017, the addition of leap seconds caused disruptions to many sites and servers in the world.
The Negative Leap Second That Never Was
The Earth’s rotation has somewhat accelerated. The next scheduled adjustment wouldn’t have been an addition, but a subtraction—a negative leap second. This has never been done before. The CGPM’s own resolution acknowledged the immense risk: “Introducing a negative leap second presents a high risk of anomalies and malfunctions for critical infrastructures”. The prospect of a negative leap second was deemed too dangerous to attempt.
How the Digital World Already Adapted
Even before the official vote, major players had already abandoned the leap second. The American GPS system, for instance, no longer intercalates seconds. Some operators prefer to smooth this intercalation over several hours, which in effect makes atomic time a little less universal. The CGPM’s decision effectively formalizes this reality, choosing stability over astronomical purity.
UTC Will Gradually Pull Away from Earth's Rotation
So, what happens now? The leap second is gone. The CGPM has acted to ensure that the gap between the astronomical unit of time and that of our atomic clocks does not exceed one hour in Coordinated Universal Time (UTC).
This means UTC will gradually pull away from the Earth’s actual rotation. For most people, this will be imperceptible. But for the systems that run our world, it’s a monumental shift.
