Why the Internet Wants the Leap Second Gone

The internet wants the leap second gone because it breaks the one rule computers rely on: time only moves forward, one second at a time. A leap second inserts an extra second, 23:59:60, to keep clocks in step with Earth’s rotation. Systems handle it in different ways, which risks errors. A vote next week could end the practice.

I love this story because it starts with something nobody notices. Your phone always shows the right time. But behind that number is a quiet negotiation between atomic clocks, a slightly wobbly planet and millions of servers that all need to agree.

This explainer is for anyone curious about how the internet keeps time. It covers what that extra second is, how your devices learn the time, and why timekeepers now want to stop adding them.

What Is a Leap Second, Exactly?

A leap second is an extra second added to Coordinated Universal Time (UTC) to keep it close to time based on Earth’s rotation. Atomic clocks tick with perfect regularity. The planet does not. Its spin is gradually slowing overall, so every so often the official clock waits one second for Earth to catch up.

The National Institute of Standards and Technology (NIST) explains the details in its leap seconds FAQ. Leap seconds are added at the end of June or December. The clock runs 23:59:59, then 23:59:60, then 00:00:00. Since the system began in 1972, NIST says, one has been added about every year and a half on average.

NIST is also blunt about the downside. Adding a second to UTC can cause problems for data logging, telecommunication systems and time distribution services. That is a polite way of saying some software simply was not built for a minute with 61 seconds.

How Your Devices Learn the Time

Your laptop does not have an atomic clock inside. It asks one. Most devices use the Network Time Protocol (NTP), which sends a short request to a time server and gets back a precise timestamp. The device then corrects for the trip across the network.

NIST runs one of the best-known sources, the Internet Time Service. Its servers are tied to UTC(NIST), the official U.S. time standard. NIST calls NTP the most commonly used internet time protocol and the one with the best performance. An older format called the Time Protocol is now used by only about 2% of its customers.

Here is a detail I did not expect. NIST says the accuracy a user sees usually depends largely on the stability of the network connection. The atomic clock is rarely the weak link. Your Wi-Fi is.

Even the source can wobble, though. NPR reported that a December 2025 windstorm cut power to NIST’s lab in Boulder, Colorado, and that a backup generator then failed. NIST said its official time ran 4.8 microseconds slow. Most people would never notice, but telecom networks and GPS-linked systems care about gaps that small.

Why an Extra Second Causes Trouble

The trouble is that not every system adds the second the same way. Some show 23:59:60. Others repeat 23:59:59 twice. A program that expects one method can stumble when it meets the other.

NIST’s own time service takes the repeat approach. Its Internet Time Service page says it handles the extra second by sending 23:59:59 twice, and it warns users in advance from the start of the last day of that month. That is sensible. It also means two clocks can disagree for a moment, depending on which method each follows.

Timekeepers have flagged this mismatch formally. In 2022, the General Conference on Weights and Measures (CGPM), the treaty body behind the metric system, passed Resolution 4 on the future of UTC. It warns that these adjustments create discontinuities that risk serious malfunctions in satellite navigation, telecommunications and energy transmission. It also notes that operators have adopted different, uncoordinated ways of handling them.

That resolution decided the allowed gap between clock time and Earth time would be widened by or before 2035. In practice, that means no more adjustments for a very long time.

The Leap Second Nobody Has Ever Tried

A new worry has pushed the timeline forward. Earth’s rotation has recently sped up. If that continues, timekeepers might need to remove a second for the first time, rather than add one.

That would be a negative leap second, and no one has ever run one. The 2022 resolution notes this scenario was never foreseen or tested. Imagine software that has spent decades preparing for an extra second suddenly being asked to skip one.

The International Committee for Weights and Measures asked its time experts to assess the risk. Their July 2026 report on Draft Resolution C describes a 2025 workshop with Earth-rotation experts. Their shared model put the chance of a skipped second in the next 10 years at about 30%, with about a 50% chance of a positive one.

Industry did not mince words. The report says companies told the committee that preparing for a skipped second could be as demanding as preparing for the Y2K bug. That comparison alone explains the urgency.

What the 2026 Leap Second Vote Would Change

The CGPM meets in Versailles, France, from October 13 to 15, 2026. A session on "Continuous UTC" is scheduled for the final day. Draft Resolution C, on keeping UTC continuous, will be introduced there.

According to the committee’s report, the draft proposes two changes.

The committee considered three options for the new limit: one minute, which would last about a century; one hour, which would last about a millennium; and no fixed limit. Users mostly asked for as few adjustments as possible, ideally none. Systems that broadcast the difference wanted a known limit, so they could size their data fields.

Why is a one-hour gap acceptable? The report makes a neat point. Time zones already put legal time up to three hours away from local solar time in some places. Daylight saving time adds a one-hour jump twice a year. We already live comfortably with bigger gaps.

Who Actually Keeps the World’s Clock?

No single country owns the time. UTC is coordinated internationally, which is why a treaty conference in France gets to decide something your phone does in Ohio. That arrangement surprises people. It is also the only way to stop each country drifting onto its own slightly different time.

The work is split up. National labs such as NIST run atomic clocks and publish their own versions of UTC. The International Bureau of Weights and Measures (BIPM) in France hosts the committees that write the rules. A separate group, the International Earth Rotation and Reference Systems Service (IERS), measures how fast Earth actually spins and announces when an adjustment is due.

That last group matters for this decision. Some countries still broadcast the gap between clock time and Earth time over radio. The committee’s report says a 2025 survey found five countries still doing so: Argentina, Canada, Russia, the UK and the US. All except Russia will probably not update their radio code, the report says, because newer methods have replaced it.

My favorite part of the process is how unglamorous it is. Nobody is voting on a grand theory of time. They are agreeing on a data format, a limit and a start date, so that every system on the planet makes the same choice at the same moment.

What It Means for You

For most people, nothing visible changes. Your phone will still show the right time. Clocks and the sun will drift apart so slowly that no one alive will notice.

The real beneficiaries are the systems you never see. Telecom networks, energy systems and satellite navigation would no longer need special code for a rare, oddly shaped minute. Fewer special cases means fewer chances for small, strange bugs. It is the same instinct behind sign-in methods that take human error out of the loop, which our explainer on why a passkey won’t work on a fake website covers.

A fair counterpoint comes from astronomers and anyone who likes clock time tied to the sky. Ending the adjustments breaks a link that has held for decades. The proposal answers that by keeping Earth-rotation data available through satellite and internet services for those who need it.

The Bottom Line on the Leap Second

The extra second solved a real problem in 1972. Today it creates a rarer but riskier one, especially with a never-tested skipped second on the horizon. Timekeepers would rather let clock time drift slowly than keep patching it.

Watch for the CGPM decision on October 15. And if you enjoy systems that change their answer under pressure, our look at why chatbots cave when you ask "are you sure?" is a fun companion read. Clocks, at least, are about to get more stubborn.