Leap seconds stop. Continuous UTC starts 20 May 2027.

The decision is a date, not a mood

Resolution 5 of the 2026 General Conference on Weights and Measures decides that continuous UTC takes effect on 20 May 2027. It sets the maximum absolute difference between UT1, the time scale tied to Earth's rotation, and UTC at 3,600 seconds. That is one hour, kept as a long-term bound the resolution says should hold for centuries. Networks, file timestamps, and certificate logs that assume UTC never steps backward are the systems this date is written for. A leap second is a one-second edit. This resolution retires that edit.the networking desk.

A negative second is the risk the text names

The resolution notes a workshop estimate that the probability of needing a negative leap second rises quickly, reaching about 30 percent by 2035. It says a negative leap second has never been applied and is treated as a high risk for infrastructure that is not prepared to remove a second. It also says different companies already smear a positive leap second in different ways, so clocks disagree across the smear. Continuous UTC is the conference's answer to both the missing negative step and the inconsistent positive ones. The 30 percent figure is the workshop's estimate, cited by the resolution, not a Futureweb calculation.what a partition does to a write.

Radio and navigation still have to carry the difference

The resolution says users of Earth orientation can read UT1 minus UTC from satellite navigation messages and from services run by the earth-rotation service and national labs. It points at ITU-R work, and at an earlier radio conference resolution, that allows the larger difference to be sent until 2035, and no later than 2040 where old equipment cannot be replaced. The civil clock goes continuous in 2027. The radio path that tells a receiver how far civil time has drifted from the Earth has a longer transition. Those are two calendars on purpose.Futureweb.

What the news accounts confirm

Nature reported that member states voted the resolution on October 15 outside Paris, and described the change as a way to avoid a negative second. CBC reported the same vote and recalled a 2022 Meta warning that a negative leap second could be damaging to software. The warning is an old comment CBC cites. The binding text is the resolution. Neither article replaces 20 May 2027 or the one-hour bound. Asked directly, How far may UTC and Earth time diverge? The resolution sets the maximum of the absolute difference between UT1 and UTC at 3,600 seconds, which is one hour. A future adjustment at that scale is a leap hour, not a leap second.the paper.

One hour is a bound, not a scheduled jump

The resolution does not insert a one-hour step on 20 May 2027. It removes further one-second steps and allows the difference to grow, up to an hour, before some later method of adjustment. A reader who plans for a missing second next spring is planning for the old system. A reader who plans for clocks to jump an hour that morning is inventing an event the decision does not contain. Asked directly, Why does the resolution say the calendar moved up? It notes a rising chance of a negative leap second, a step that has never been inserted, and it treats that step as a disruption for systems that were not built to remove a second.

Who has to care before 2027

Anyone who runs a clock that inserts or rejects leap seconds: time servers, exchanges, telecom synchronisation, and software that special-cases 23:59:60. The resolution asks the timekeeping bureau to keep working with the telecom union, astronomers, and the earth-rotation service so the operational announcements change with the decision. A household laptop that only displays civil time will follow whatever the operating system does with the bulletin. The bulletin is the artifact.a version number still has to mean something.

What this page will re-check

A circular that names the last leap second, if any, before 20 May 2027. An ITU update that shortens or extends the radio transition. A revision of Resolution 5 itself. Until those exist, the adopted text is the record: continuous UTC on that May date, and a one-hour ceiling on the drift from Earth time. Asked directly, When does continuous UTC start? The resolution decides that continuous UTC becomes effective on 20 May 2027. The vote was on 15 October 2026, at the 28th meeting of the General Conference on Weights and Measures.

What the resolution does not redefine

A companion resolution, described in the time committee president's statement the same day, sets work toward a possible new definition of the second in 2030. That is a different decision. Resolution 5 does not replace the caesium second. It changes how UTC is kept close to the Earth. Mixing the two would invent a new second this vote did not adopt. A clock that only moves when one region's control plane agrees is a different failure, already filed.when one region is the control plane.

What stays specific

15 October 2026, Resolution 5, continuous UTC from 20 May 2027, a 3,600-second ceiling, a negative leap second that has never been used, and a radio transition that can outlast the civil change. Nature and CBC confirm the vote. They do not renumber the date. The short answer this page will stand on is this: Resolution 5, adopted on 15 October 2026, says continuous UTC takes effect on 20 May 2027 and that the difference between UTC and Earth-rotation time may reach 3,600 seconds. Nature and CBC reported the vote. The resolution's reason is the risk of a negative leap second, which has never been applied.