UTC will stop using leap seconds from May 20, 2027

The General Conference on Weights and Measures decided that Coordinated Universal Time, UTC, will become continuous from May 20, 2027.

The decision was adopted on October 15 at the twenty-eighth General Conference on Weights and Measures. Its resolution raises the maximum difference between UTC and the Earth-rotation time scale UT1 to 3,600 seconds, allowing UTC to remain continuous for several centuries.

Leap seconds currently reconcile atomic time with Earth's irregular rotation. Only positive leap seconds have previously been used. Faster rotation creates the possibility that the existing rules would require a second to be removed for the first time.

The resolution says a negative leap second could disrupt infrastructure that depends on precise synchronization. The concerns include transportation, energy distribution, telecommunications and space systems.

Leap years address a different issue, aligning the calendar with Earth's orbit around the Sun. Changing UTC corrections does not abolish leap years.

The International Bureau of Weights and Measures was instructed to work with relevant international organizations to inform users about the transition and continue monitoring the difference between UT1 and UTC.