Time now · 4 min read
The future of UTC: why leap seconds are under review
International timekeepers are reconsidering leap seconds. Here is what is decided, what remains open and why it matters.
A leap second is a small adjustment with a large operational footprint. The international community is working toward a more continuous UTC, but headlines about 'abolishing time changes' can obscure what the decision actually covers.
The mismatch behind the debate
UTC is based on atomic timekeeping while the orientation of Earth is described by astronomical time, called UT1. Earth's rotation varies, so the two scales gradually separate. Leap seconds have historically kept that difference small by adding an occasional second to UTC. The last insertion was in 2016; a new one is not a regularly scheduled event.
A discontinuity is awkward for software that assumes every minute has 60 seconds. Systems may represent an inserted second differently, making logs and synchronization more complicated. The challenge is not that most clocks visibly fail; it is that independently designed networks have to agree on the same instant.
What has been decided
In 2022, the General Conference on Weights and Measures resolved to increase the permitted difference between UTC and UT1 by or before 2035. The aim is to avoid frequent leap-second adjustments over a long period. The resolution started further work on the maximum permitted difference and how to implement the change across institutions.
A policy direction is not an instant switch. Other standards bodies, navigation providers and national time services are involved in delivering and interpreting time. Draft proposals can change; treat any specific future effective date as provisional until adopted by the responsible bodies.
What changes for you
For normal appointments, nothing changes today: your device's time zone and maintained time libraries still determine the local display. The debate does not abolish daylight saving time, which is a separate civil policy. It is about the reference scale behind precise synchronization.
If you operate systems that require subsecond ordering, consult your time-service provider's documented handling of leap seconds. If you use a browser timer, do not manually add or subtract a leap second to a future calendar date. Let maintained platforms handle the standard and verify important event times close to the date.
Sources & further reading
These sources provide the underlying standards or research. This guide is educational and is not medical advice.