No, Earth is not getting a new 24-hour day. The General Conference on Weights and Measures (CGPM) has changed how civil time tracks the planet’s rotation. From 20 May 2027, continuous Coordinated Universal Time (UTC) will no longer use routine leap seconds to keep clocks within one second of Earth-rotation time (UT1). UTC will remain based on atomic time, while its permitted difference from UT1 can grow to 3,600 seconds—one hour.
What changes on 20 May 2027?
At its 28th meeting in October 2026, the CGPM adopted Resolution 5 on the continuity of UTC. The resolution says continuous UTC becomes effective on 20 May 2027 and sets the maximum permitted value of |UT1−UTC| at 3,600 seconds (one hour). Read the full wording in the BIPM Resolution 5 (2026).
As an Amazon Associate I earn from qualifying purchases.
Until the change takes effect, international timekeeping can insert a leap second when Earth’s rotation causes UT1 to approach one second ahead of or behind UTC. Afterward, UTC will be generated continuously from atomic time without those routine one-second steps. The difference from solar-based UT1 will be monitored and allowed to accumulate within the new one-hour limit.
Recommended Free Tools
The old and new systems
| Feature | Before 20 May 2027 | Continuous UTC after 20 May 2027 |
|---|---|---|
| Synchronization target | UTC kept within one second of UT1 | UTC may differ from UT1 by up to 3,600 seconds (one hour) |
| Clock behavior | Occasional one-second leap-second steps | No routine leap-second steps |
| Time basis | Atomic time adjusted to follow Earth rotation | Continuous atomic-time scale, with increasing solar-time offset |
| Main risk | Software and infrastructure errors during an unexpected step | Long-term divergence between civil UTC and apparent solar time |
| Who notices most | Systems requiring sub-second coordination | Future generations and organizations needing a close solar-time relationship |
Why leap seconds are being retired
Earth does not rotate at a perfectly constant rate. Tides, movement in the atmosphere and oceans, and processes inside the planet make the length of a solar day vary. Atomic clocks provide a far more stable frequency, so UTC needs a policy for reconciling those two clocks.
#1 Best Overall
- Atomic Clock Digital - The clock has a built-in receiver that automatically synchronizes itself with WWVB radio broadcast, which will set and update time automatically every midnight, no need to set manually. It has four time zones selectable: EST, PST, MST, CST.
- Digital Wall Clock Battery Operated - This digital clock is supported by 3xAAA battery (Not included). No wires make it can be placed anywhere; and the low battery symbol reminds you to replace the battery in time to avoid getting the wrong time due to low power.
- Digital Wall Clock Large Display - The LCD screen measures 6.2 in x 3.7 in and it displays time, indoor temperature, day and date. Each section is showed separately, allows you to read the content easily and quickly.
- Atomic Clock with Auto DST - With DST on, the time would go forward or backward one hour automatically in daylight saving time, no worry about time changing on that day. If for no need, it could also be turned off, then “AUTO DST” disappears from screen.
- Digital Alarm Clock - The alarm could be turned on or off according to your need, just click the button to set. When alarm is set on, there is a bell icon staying on screen. The icon will disappear if alarm is set off. When alarm goes off, just click any button to stop it on the day.
The current approach creates an operational problem: a leap second is an irregular discontinuity that must be handled simultaneously by networks, databases, navigation systems, exchanges, telecom equipment and industrial controllers. Dr Christian Bizouard of the International Earth Rotation and Reference Systems Service summarized the concern: “When we apply leap seconds, there are always errors.” His statement appears in the 15 October 2026 AOL/The Telegraph report.
The CGPM resolution records a 2025 Consultative Committee for Time and Frequency/IERS workshop estimate that the probability of a negative leap second could reach 30% by 2035. A negative step has never been applied, making its behavior in unprepared systems especially uncertain.
How often have leap seconds occurred?
Contemporaneous reporting says 27 leap seconds were inserted from the 1970s through 2016; the last occurred in 2016. The same report links the 2012 leap-second event to problems or crashes reported by Mozilla, Reddit, Foursquare, Yelp, LinkedIn, StumbleUpon, Linux and Java systems. These are reported implementation incidents, not a controlled measurement of every platform’s behavior. The report also estimates that civil time could drift from solar time by about 25 minutes over 500 years if no corrective steps are made. See the full report for that historical context.
What’s actually slowing this PC down?
Pick the symptom - the matching free tool is one click away.
Rank #2
- Atomic Wall Clock Never Need Setting: Atomic clock has a built-in receiver that automatically synchronizes itself with the WWVB radio broadcast by the US Government's National Institute (NIST) in Fort Collins, Colorado. The Atomic Clock will always be accurate to within one second as it receives daily WWVB updates. (No Backlight)
- Atomic Clock with Indoor/Outdoor Temp: The Wireless outdoor sensor transmits the outdoor temperature to the atomic clock. The sensor should be placed within 100ft of the clock. Also, clock has a built-in high-quality indoor temperature sensor so that you can read the temperature both indoor and outdoor
- Digital Wall Clock Large Display: Jumbo 2.5 inch Height Time Digital Display - Use as either a wall clock or as a desk clock, it is easy to read, easy to Use and easy to set up. This atomic clock has been designed with absolute simplicity in mind, you can also set it manually. Excellent clocks for seniors, suitable for anyplace in your home or office
- Atomic Clock Digital: 12/24 Hour time formats with accurate and clear second minute and hour display; 4 time zone to choose (PST, MST, CST, EST); auto daylight saving time; temperature display units in Celsius or Fahrenheit
- Digital Wall Clock Battery Operated: Both clock and outdoor sensor are supported by batteries only, no need to plug or charge (Batteries not included). The existed alarm features can wake you up in the morning or help you keep track of dates and days of the week to avoid missing any important meetings or appointments
Does a day stop being 24 hours?
No. “Day” can mean several different things. The conventional civil day still has 24 hours, each hour 60 minutes and each minute 60 seconds. UTC timestamps, schedules and time-zone offsets continue to use that system.
Earth’s physical rotation will remain variable. An observed solar day is approximately 24 hours but is not exactly the same length every day. Continuous UTC changes the reference used by clocks and computers; it does not speed up, slow down or otherwise alter Earth.
Will sunrise and sunset change?
Sunrise, sunset and the Sun’s position in the sky are determined by Earth’s rotation, your location and the date. They will occur at the same physical moments they would have occurred without the policy change. What changes slowly is the label on the civil clock: over centuries, UTC noon will move farther from the instant when the Sun is highest at Greenwich.
Rank #3
- [Automatic Time Updates] – The Atomic Time Feature conveniently allows the clock to sync with the WWVB radio transmission from Fort Collins, CO, for accurate time updates.
- [Classic design] – With unmatched attention to detail, the WT-3129B is highlighted by a distinctive matted 12-inch black frame with a silver bezel – a statement piece for any home setting.
- [5-Year Battery Life] – A quality set of 3 “AA” batteries will keep the clock running for up to 5 years – an impressive feat offering unparalleled convenience and peace of mind.
- [SIMPLE-SET] Simple adjustable switch to your Time Zone (4 different selections: PT-Pacific, MT-Mountain, CT-Central, ET-Eastern)
- [A Brand You Can Trust] – Family-owned and operated since 1983, La Crosse Technology is the world leader in Atomic Time and Weather Instruments. Designed in La Crosse, WI, our products have unmatched support resources, including printed setup guides, helpful video tutorials, and lifetime access to our USA-based tech support team.
That drift is gradual rather than a sudden one-hour jump. Time zones already differ from local apparent solar time by up to many hours, and everyday schedules are set by local time-zone rules, not by a requirement that UTC noon match the Sun.
Windows Errors? Fix Them Before They Spread
Repair common Windows errors and clear accumulated junk for a smoother, more stable PC - no reinstall needed.Free scan · no reinstallOutdated Drivers Are Slowing You Down
One free scan finds every outdated or missing driver and matches the right update for your exact hardware.Free scan · exact hardware matchWho needs to prepare?
Most people
Phones, laptops, watches and household clocks will continue displaying local time through their normal time-service updates. A consumer “radio-controlled atomic clock” receives an atomic-time-based civil signal; it does not measure Earth’s rotation or predict sunrise.
Critical and distributed systems
Transportation, energy distribution, telecommunications, financial infrastructure, scientific facilities and space projects often coordinate events at sub-second precision. For these operators, removing an irregular one-second step simplifies timestamp ordering and control logic, but it also makes the long-term UTC–UT1 offset a planning issue.
Rank #4
- Atomic Clock with Backlight: Never Need Setting, a built-in receiver that automatically synchronizes itself with the WWVB radio broadcast, it will always be accurate to within one second as it receives daily WWVB updates. Three levels (OFF-LOW-HIGH) backlight helps you to know what time it is without turning the light on late at night
- Large Digital Wall Clock: 14 inches large display with 4.3 inches numbers make this digital wall clock easy to read and it's visible around the entire room, friendly to the elderly and the visually impaired
- Digital Wall Clock Battery Operated: The clock is supported by four AA battery (not included). No wires make it can be placed anywhere; and the low battery symbol reminds you to replace the battery in time to avoid getting the wrong time due to low power
- Digital Clock with Date and Day of the Week: This digital wall clock with backlight not only does it give you the time, you can also get the day, date and current indoor temp at just a glance. And the day and temp display could be chosen to display alone or in turns every 10s
- Multiple Display Formats: Large digital wall clock with backlight makes it easy to know the time, two different time and temperature formats (12/24H; /) are available for your convenience and preference
- Inventory every component that assumes UTC is always within one second of UT1.
- Check time-service, GNSS, broadcast and data-center documentation for the 20 May 2027 transition.
- Keep leap-second parsing for historical timestamps; old data will still contain past leap seconds.
- Define whether applications need UTC, a monotonic clock, or an Earth-rotation reference such as UT1.
- Monitor authoritative bulletins and test failover paths before the effective date.
What “continuous UTC” means for the future
Metrologist Noel Dimarcq of the Côte d’Azur Observatory called the decision “a historical moment” and “an international reference time scale continuous for the next millennia” in the 15 October 2026 report. The practical trade-off is clear: computer systems receive a smoother, continuously increasing time scale, while civil time and solar time gradually separate.
The one-hour ceiling is not a promise that the offset will reach one hour soon. Earth-rotation forecasts determine how quickly UT1 and UTC diverge, and the new policy permits that divergence rather than correcting it with routine leap seconds.
Free tools Windows power users keep installed
One-click scans. No signup required.
Frequently Asked Questions
When does continuous UTC begin?
The CGPM resolution sets 20 May 2027 as the effective date.
Best Value
- SIGNATURE READABILITY & ATOMIC PRECISION: See the time clearly from across the room with bold custom numerals, ultra-white contrast, and a large 14" face. Daily atomic syncing keeps time accurate automatically with no drifting. Designed for instant visibility in homes, offices, schools, and shared spaces. For use in the lower 48 states only. Not recommended for Hawaii, Alaska, or international use
- SELF-SETTING, ZERO HASSLE: Insert the included AA battery, select the time zone, set daylight savings, and press reset. The clock automatically syncs to the official U.S. atomic signal from Fort Collins, Colorado and keeps precise time year-round with no manual adjustments. Not for use in Alaska or Hawaii
- PREMIUM MATERIALS, INDOOR OR OUTDOOR: Glass lens, satin-finish dial, durable black frame, and weather-resistant rear battery cover support dependable indoor or covered outdoor use. Suitable for kitchens, patios, porches, garages, break rooms, pool houses, and classrooms
- LARGE SPACE VISIBILITY & EVERYDAY USE: Suitable for living rooms, kitchens, offices, schools, lecture halls, factories, gyms, and covered outdoor areas. Easy across-room readability helps families, professionals, students, and seniors stay confidently on time
- BOLD DESIGN ELEMENTS: Features large black numerals on a crisp white face inspired by highway signage, a bold red second hand, and premium glass lens that deliver clear visibility from any angle and complement various decor styles including modern, Scandinavian, industrial, or traditional
What replaces leap seconds?
Nothing replaces them with another periodic clock adjustment. UTC will continue from atomic time, while its monitored difference from UT1 may grow to one hour.
Do I need to change my phone or watch?
Usually not. Consumer devices will continue receiving ordinary civil-time updates; specialist systems should follow their vendor’s transition guidance.
Quick Recap
Product prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on Amazon at the time of purchase will apply.
