No more leap seconds

2026-10-16

The General Conference on Weights and Measures (CGPM) decided on 15 October 2027 that Coordinated Universal Time (UTC) will not be adjusted by leap seconds anymore, but instead by leap hours.

Since 1972, UTC has been adjusted by 27 leap seconds to compensate for deviations in the Earth's rotation speed. Leap seconds, and especially negative leap seconds (which have never been applied), pose technical challenges to systems that require precise timekeeping.

Leap hours are much easier to deal with, since the implementation would be similar to a time zone change or the start or end of daylight saving time. One leap hour is also considerably more convenient than 3,600 leap seconds, especially when the problem can be deferred a few thousand years into the future.

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No more leap seconds

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