Time's up for the leap second

The world is about to stop adding leap seconds. 

Under the new system, clocks will be allowed to drift from the Earth's actual rotation by up to an hour before anyone has to step in. This means no more leap seconds – for centuries.

Leap seconds have been added to Coordinated Universal Time (UTC) to keep it aligned with Earth's irregular rotation. But these adjustments can disrupt digital systems that rely on continuous, precise timekeeping. Since the practice began, 27 leap seconds have been inserted. In 2012, a leap second reportedly caused outages across more than 2,000 networks worldwide. In 2015, the US Intercontinental Exchange halted trading for more than 60 minutes.

The risk of a negative leap second – removing a second rather than adding one – has also raised concerns, as computer systems have never had to implement one on a global scale.

The reform comes after the 28th General Conference on Weights and Measures (CGPM), held in Versailles, France, adopted a resolution this month to introduce continuous UTC from May 20, 2027.

Sometimes described as a shift from leap seconds to a "leap hour," the change is expected to cut maintenance and testing costs for internet services, cloud computing and financial markets.

For most people, the impact will be negligible. Astronomical observations and other applications that depend on Earth's rotation can keep using data that accounts for the difference between the two time scales.