The Leap Second Is No More
BIPM will stop issuing leap seconds from 20 May 2027, ending a system used to keep atomic-clock time aligned with Earth’s rotation. The change matters because leap seconds have disrupted computer systems and the risk of a negative leap second, which could cause more serious failures, has increased.
Since 1972, 32 leap seconds have been added to Coordinated Universal Time, most recently in 2016. Earth’s changing rotation, affected by factors including tides and melting ice, causes the difference between atomic time and astronomical time; a 2024 study suggested a negative leap second might otherwise have been needed as soon as 2029. BIPM chose the 2027 date after industry tests found failures with a negative leap second.
- Leap seconds will end in May 2027.
- 32 have been added since 1972.
- Avoiding a negative leap second could prevent system failures.
Both sides, in good faith
The strongest fair case each way — we don't pick a winner.
The case for
Ending leap seconds could make timekeeping more reliable for digital systems that depend on consistent timestamps, after leap-second adjustments have caused disruptions and tests found failures with a negative adjustment. A planned change also gives technology and standards bodies a clearer basis for coordination, while astronomical time can still be tracked separately for applications that need it.
The case against
Keeping leap seconds preserves the close link between civil time and Earth’s rotation, which some people see as important for navigation, astronomy and the public understanding of time. Removing them would allow atomic time to drift further from the day-night cycle, potentially leaving future generations to manage a larger correction and shifting costs onto fields that rely on the relationship between clocks and the sky.