The Upcoming Cancellation of Leap Seconds and Its Impact on Programmers

Leap seconds, the only phenomenon that can get tech giants like Meta, Google, Microsoft and even Linus Torvalds to agree, are finally slated for cancellation.

At the 27th International Earth Rotation and Reference Systems Service (IERS) meeting, representatives passed a resolution to stop adding leap seconds to official clocks starting in 2035.

The concept of a leap second was first introduced by the International Earth Rotation Service (IERS) in 1972 to keep atomic time aligned with the Earth's rotation. There are two time‑keeping systems: World Time (based on Earth's rotation) and Atomic Time (based on atomic transitions). Everyday devices display atomic time, but because Earth's rotation is irregular, the two systems gradually diverge.

When the difference reaches 0.9 seconds, a leap second is inserted to bring the systems back into alignment.

Since 1972, 27 leap seconds have been added, each causing occasional computer glitches. Notable incidents include the 40‑minute Reddit outage in June 2012, simultaneous crashes of sites like Mozilla and LinkedIn, and the 2015 global network disruptions that halted about 2,000 networks and forced the NYSE to suspend trading for 61 minutes.

The decision to cancel leap seconds is a programmer’s relief, but it won’t be implemented until 2035, meaning today’s developers must wait over a decade to reap the benefits.

Not everyone supports the move; Russia, for example, prefers a later cancellation (around 2040) to accommodate adjustments to its GLONASS satellite navigation system.

Scientists warn that without leap seconds, time will drift from World Time by about one minute in 50 years, ten minutes in 300 years, and an hour in 900 years, eventually causing noticeable shifts in daily schedules.

In the meantime, programmers may need to continue battling leap‑second issues for many more years.