Global Clock Ends Leap Seconds in 2027
Timing systems that power networks and satellites gain a one-hour tolerance from Earth's rotation starting May 20, 2027.
Updated on Nov. 4, 2026 in Space
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The General Conference on Weights and Measures adopted a decision on October 15, 2026, to end the addition of leap seconds to Coordinated Universal Time (UTC). The permitted difference between UTC and Earth's rotation-based time will rise to one hour on May 20, 2027, after which leap seconds stop. The change is an adopted international decision, not a rollout of a new technology.
Why it matters
Leap seconds have been added to UTC since 1972, and the last one was added on December 31, 2016. The shift reflects growing concern that abrupt time corrections could disrupt computer networks, telecommunications, electricity grids and satellite navigation, which depend on steady timing.
The decision sets a new permitted difference of 3,600 seconds between UTC and Earth's rotation-based time, up from its current limit. Experts estimate a 30% probability that a negative leap second may be needed by 2035, a projection the source does not verify.
The players
Bureau International des Poids et Mesures (BIPM)
The Sèvres, France-based international body that maintains the SI system and will implement the decision with international organizations.
General Conference on Weights and Measures (CGPM)
The intergovernmental body that governs the International System of Units and adopted the end of leap seconds.
The details
Coordinated Universal Time is the global reference clock, and it has been kept close to Earth's rotation by inserting leap seconds, one-second adjustments to the clock. Earth's rotation does not run at a perfectly constant speed, while atomic clocks, which count time from the vibrations of atoms, are extremely stable. Raising the permitted gap to 3,600 seconds removes the need to insert further leap seconds into UTC, and the change does not add an hour to the day or alter everyday clock times.
Timeline
1972: Leap seconds first added to UTC.
December 31, 2016: Last leap second added to UTC.
October 15, 2026: The General Conference on Weights and Measures adopted the end of leap seconds.
May 20, 2027: The permitted UTC difference becomes one hour and leap seconds stop.
The Tech Race
The decision sets the international timekeeping standard for the coming decades, shaping how satellite navigation, telecommunications and grid operators synchronize their systems. It settles a long-running debate between astronomical time and atomic time in favor of stable atomic timekeeping.
The change does not add an hour to the day or alter everyday clock times. Different technology providers handle leap seconds differently, so the practical effect on networks and devices will depend on how each one implements the new standard.
The takeaway
Watch for how major network, telecom and satellite navigation providers announce their implementation plans before the May 20, 2027 changeover. The source notes that the BIPM will work with international organizations on implementation.
What happens next
On May 20, 2027, the permitted UTC difference becomes one hour and leap seconds stop being added.
Further reading
For broader context on how timekeeping shapes orbital systems, explore the Space section.
Source note: This article includes information reported by GreekReporter.
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