Leap seconds and continuous UTC

What a leap second is

Atomic clocks keep time more steadily than the spinning Earth. To keep UTC within 0.9 seconds of Earth-rotation time, one extra second was inserted at the end of a UTC day, 27 times between 1972 and 2016. That is why TAI, the continuous atomic scale, is now 37 seconds ahead of UTC (it began 10 seconds ahead in 1972). GPS time ignores leap seconds and started level with UTC in 1980, so it is 18 seconds ahead today.

The end of leap seconds

On 15 October 2026 the General Conference on Weights and Measures voted to stop adding leap seconds. From 20 May 2027 UTC runs continuously. Without leap seconds the gap between UTC and Earth-rotation time will slowly grow; press reports mention it could reach about an hour over a very long time, and how that gap will be handled has not been settled in anything we could confirm. Check the BIPM for the official text.

Until then the offsets above stay as they are: the last leap second was at the end of 31 December 2016. The offsets on this page are fixed numbers, and they will not change after 2027 unless the rules change again.

All 27 leap seconds

1972-06-30, 1972-12-31, 1973-12-31, 1974-12-31, 1975-12-31, 1976-12-31, 1977-12-31, 1978-12-31, 1979-12-31, 1981-06-30, 1982-06-30, 1983-06-30, 1985-06-30, 1987-12-31, 1989-12-31, 1990-12-31, 1992-06-30, 1993-06-30, 1994-06-30, 1995-12-31, 1997-06-30, 1998-12-31, 2005-12-31, 2008-12-31, 2012-06-30, 2015-06-30, 2016-12-31. Each was added at the end of the UTC day shown, as 23:59:60.