Continuous UTC to take effect on May 20, 2027

The General Conference on Weights and Measures has approved continuous Coordinated Universal Time, or UTC, from May 20, 2027, ending the need for leap-second adjustments.

The resolution of the conference's twenty-eighth meeting sets the new limit for the difference between UT1 and UTC at 3,600 seconds. It says this will preserve continuous UTC for several centuries. Implementation coincides with World Metrology Day.

UT1 reflects Earth's uneven rotation, while atomic time relies on stable physical processes. Since 1972, twenty-seven leap seconds have been added to UTC to keep it aligned with the planet's rotation.

The resolution highlights the possibility of a first negative leap second, which would remove a second from the count. It identifies risks of disruption to infrastructure relying on precise synchronization, including transport, energy, telecommunications and space projects.

The International Bureau of Weights and Measures has been tasked with supporting implementation alongside relevant organizations and continuing to monitor the difference between UT1 and UTC.