Computing

Leap Seconds to Be Retired Next Year by International Body

The international organization maintaining the International System of Units has moved up the retirement of leap seconds to prevent computer system disruptions.

Radwan AbdulhadiEditor and technology writer

Published: October 18, 2026 · Updated: October 18, 2026 · 3 min read

Leap Seconds to Be Retired Next Year by International Body — Image: Tom's Hardware

Retirement Date Moved Up to 2027

The International Bureau of Weights and Measures (BIPM), which maintains the International System of Units (SI), has voted to expedite the retirement of the leap second. According to reporting from [ Tom's Hardware ](https://www.tomshardware.com/tech-industry/international-measurement-organization-to-retire-leap-seconds-next-year-to-avoid-wreaking-havoc-on-computer-systems-group-makes-move-to-simplify-atomic-time-tracking), the organization has moved forward the planned retirement date from 2035 to May 20, 2027. This crucial adjustment is intended to prevent disruptions in computer systems that inherently expect a consistent sixty seconds every minute. Further details are available from Tom's Hardware in the original source material.

The leap second has historically been added to Coordinated Universal Time (UTC) to ensure it stays in sync with the Earth's rotation. However, planetary movement is not a constant one revolution every 24 hours, driven by forces from the atmosphere, oceans, Earth's core, and the Moon. Data indicates a thirty percent probability of needing a negative leap second by 2035 if the system remains unchanged.

Risks of Negative Leap Seconds

A positive leap second previously added an extra second in the year it was applied, such as when clocks went to 23:59:60 on December 31, 2016, before shifting to 00:00:00 on January 1, 2017. While positive leap seconds have posed challenges, a negative leap second has never been applied before in practice.

The BIPM noted that a negative leap second poses a high risk of causing anomalies and disruption to critical infrastructures that are largely unprepared for the shift. The organization estimated that the required financial investment to prepare systems for this event would be comparable to preparations made for the millennium bug.

Historical Impact on Tech and Infrastructure

Leap seconds have previously caused notable problems for major websites and technology companies. For instance, Reddit famously suffered a crash following the addition of a leap second back in 2012.

While standard desktop personal computers may not be heavily affected if their time service servers are updated, national critical infrastructures remain vulnerable. Sectors such as transportation, energy distribution, telecommunications, and space projects could face severe disruptions if a negative leap second were enforced.

Introduction of the Leap Hour

Instead of requiring extensive software upgrades and hardware replacements over the next decade, the international standards body decided to scrap the leap second entirely. It will be replaced by a leap hour next year, ensuring long-term continuity for UTC, which is expected to remain in sync with TAI for several centuries.

While a one-hour time jump may seem shocking when it eventually occurs in the distant future, the BIPM points out that similar adjustments already exist. Many countries experience differences of more than one hour between local apparent solar time and civil time due to chosen time zones, alongside regular daylight-saving time adjustments.