Why Leap Seconds May Disappear by 2035

Every clock appears to move at a steady pace, but modern technology requires a more precise definition of time than daily routines do. Atomic clocks measure seconds with extraordinary consistency, while Earth’s rotation varies slightly because of tidal forces, movements inside the planet, ocean and atmospheric circulation, earthquakes, and changes in the distribution of mass.

For decades, international timekeepers have reconciled these differences with leap seconds. That system may soon change. International authorities have agreed to work toward eliminating leap-second adjustments by 2035, although the final replacement has not yet been selected. Source 1

The change will not alter the physical passage of time. It will change how global clocks are coordinated.

How Time Is Measured Today

Atomic clocks define the modern second

The modern second is based on the stable behavior of atoms rather than the length of a day. Atomic clocks measure the frequency of atomic transitions and use it as a highly consistent reference.

This method is more reliable than using Earth’s rotation. The exact duration of a day varies by tiny amounts, while atomic clocks continue counting seconds uniformly regardless of sunrise, seasons, or changes in rotational speed.

Atomic clocks support GPS and other satellite-navigation systems, telecommunications networks, internet infrastructure, financial transactions, cloud computing, scientific experiments, electricity grids, transport systems, and tests of fundamental physics. Their precision also supports international time standards and research into small changes in physical systems. Source 7

Coordinated Universal Time connects clocks worldwide

Coordinated Universal Time, or UTC, is the international reference for civil time and many technical systems. Time zones are defined in relation to UTC, while computers, telecommunications networks, navigation systems, and financial platforms use it to coordinate events across borders.

Two forms of time are especially important:

• Atomic time advances according to atomic clocks.
• Astronomical time reflects Earth’s actual rotation.

UTC has historically remained close to astronomical time by adding occasional leap seconds. This kept the difference small enough for noon to remain broadly connected to the Sun’s position. Digital networks now exchange timestamps continuously across millions of devices, making irregular adjustments harder to manage.

Why Earth’s day length varies

Earth does not rotate at exactly the same speed every day. Influences include:

• Tidal friction caused by the Moon
• Movements in Earth’s mantle and core
• Ocean currents
• Atmospheric circulation
• Earthquakes
• Changes in ice and water distribution
• The redistribution of mass across the planet

These variations are insignificant in ordinary life but important when computer systems and scientific instruments must align timestamps precisely.

What Is a Leap Second?

A leap second is an occasional one-second adjustment added to UTC to prevent atomic time and Earth-rotation time from drifting too far apart. It is similar in principle to a leap year, although it addresses a different problem: Earth’s rotation does not produce perfectly uniform days.

Leap seconds are not scheduled annually. International timekeeping organizations monitor Earth’s rotation and compare it with atomic time. An adjustment is introduced when the difference approaches an accepted limit, usually at the end of June or December.

Most people never notice a leap second. Devices generally receive time updates automatically, and the extra second does not make a day feel longer. The challenge is digital coordination. A leap second can produce a repeated timestamp, an apparent reversal, records that appear out of order, or conflicts between synchronized systems.

Why Leap Seconds Are Difficult for Technology

Many software systems assume that timestamps progress continuously and strictly increase. During a leap second, a system might record an event at 23:59:59, record another event during the same displayed second, and then advance to 00:00:00. Software that expects every timestamp to be unique may fail.

Modern infrastructure magnifies these risks. Cloud platforms distribute workloads across data centers, telecommunications networks coordinate transmissions, payment systems verify events in sequence, and satellite-navigation services calculate positions from signal timing.

Other systems that depend on accurate clocks include:

• Stock exchanges and banking networks
• Authentication and security-certificate services
• Distributed databases
• Electricity grids and industrial controls
• Rail and aviation infrastructure
• Scientific sensor networks

Different operating systems, protocols, databases, and service providers may handle leap seconds by repeating a second, pausing briefly, or spreading the adjustment over time. When connected systems use different methods, their records can disagree.

The Planned Change by 2035

International timekeeping authorities have agreed to work toward eliminating leap-second adjustments by 2035. The goal is to let UTC progress continuously instead of inserting occasional seconds to follow Earth’s irregular rotation. Source 1

This is not an immediate change to every clock. It is a gradual international effort involving measurement institutes, standards organizations, satellite-navigation operators, technology companies, telecommunications providers, financial institutions, and scientific communities.

Eliminating leap seconds would not make seconds longer or shorter, stop atomic clocks, remove time zones, regularize Earth’s rotation, or require people to reset household clocks. It would mean that UTC no longer used occasional inserted seconds to stay closely aligned with Earth’s rotation.

Over time, the difference between atomic and rotational time could grow. The central question is how much divergence should be accepted and how future systems should manage it.

Possible Alternatives

Allowing a larger gap

UTC could remain continuous while allowing a larger difference between it and Earth-rotation time. This would simplify software and infrastructure but gradually separate clock time from the Sun’s position.

Using gradual corrections

A correction could be distributed over a longer period instead of inserted as one visible second. This would reduce abrupt changes, but every participating system would need to use the same duration, rate, notification process, and rules for older systems.

Maintaining separate time scales

Technology could use a continuous technical reference while astronomers and other researchers continued to track Earth’s rotation independently. Reliable conversion tools would be necessary for observatories, satellite operators, navigation organizations, and scientific instruments.

Why Atomic Clocks Matter

GPS and similar systems calculate position partly by measuring how long signals take to travel between satellites and receivers. Because radio signals travel rapidly, a small timing error can create a meaningful position error. Atomic clocks provide the precision needed for aviation, shipping, mapping, emergency response, agriculture, and mobile devices.

Telecommunications networks use synchronized equipment to move data efficiently. Internet services rely on timestamps for authentication, security certificates, event logs, data replication, monitoring, fraud detection, and troubleshooting.

Financial systems use timestamps to order transactions and investigate disputes. Researchers compare observations from instruments in different locations. Power grids and other critical infrastructure use coordinated timestamps to monitor equipment and respond to failures.

Leap Seconds Are Not Daylight Saving Time

Leap seconds and daylight saving time address different problems:

• Leap seconds reconcile atomic time with Earth’s rotation.
• Daylight saving time shifts local clocks to place daylight at different times of day.

Leap seconds concern the global time standard. Daylight saving time is determined by national or regional law. Eliminating leap seconds would not automatically end seasonal clock changes. Source 5

What Will Change for Ordinary People?

Most daily routines will remain unchanged. People will continue using familiar hours, minutes, seconds, and time zones. Smartphones, computers, watches, and household clocks will continue displaying local time, and sunrise and sunset will not suddenly change.

The main changes will occur behind the scenes. Software providers, network operators, satellite-navigation organizations, and standards bodies will manage the transition. Businesses that depend on precise timestamps may need to review their systems, while scientific and navigation organizations may need conversion tools linking continuous technical time with Earth-rotation measurements.

Conclusion

Time itself is not changing. Earth will continue rotating irregularly, and atomic clocks will continue measuring seconds with extraordinary precision.

What may change is the method used to coordinate those realities. Leap seconds have kept UTC close to Earth’s rotation, but they are difficult for interconnected digital systems to process. International timekeepers are therefore working toward continuous global time without occasional inserted seconds.

Most people will notice little. The larger changes will occur inside navigation systems, communications networks, financial platforms, scientific instruments, and the infrastructure supporting the internet.

Every second still matters. The question is whether every second must also be adjusted to match Earth’s changing rotation.

FAQ

What is a leap second?

A leap second is an occasional one-second adjustment added to UTC to keep atomic time close to time measured by Earth’s rotation.

Why are leap seconds expected to be eliminated?

They can create repeated or irregular timestamps that computer networks, databases, navigation systems, and other digital infrastructure may handle inconsistently.

When will leap seconds end?

International timekeepers have agreed to work toward eliminating leap-second adjustments by 2035. The implementation plan is still being developed.

Will eliminating leap seconds change the length of a day?

No. Earth’s rotation will continue to vary naturally. The change affects how global time standards account for that variation.

Will this affect daylight saving time?

No. Leap seconds concern global time coordination, while daylight saving time changes local clocks seasonally.

Will people need to change their clocks?

Most people will not need to make manual changes. The main adjustments will involve technical standards, software, networks, scientific systems, and infrastructure that depends on precise time.