Leap seconds list

Leap Seconds Inserted into the UTC Time Scale

1. How many leap seconds have there been?
2. How do you calculate leap seconds?
3. What is leap second in NTP?
4. When was the last time a leap second was added?

How many leap seconds have there been?

There have been 27 leap seconds added since 1972. In a post on Meta's engineering blog, Oleg Obleukhov and Ahmad Byagowi say 27 is quite enough for non-solar-scientist types—"enough for the next millennium."

How do you calculate leap seconds?

The average speed of Earth's rotation is measured by Universal Time (UT1). When the difference between UTC and UT1 is predicted to reach 0.9 seconds within 12 months, a leap second is added to UTC and clocks worldwide. In other words, our clocks are always kept within a second of the average length of a day.

What is leap second in NTP?

Leap second is handled as a one-second offset accumulated at 00:00:00 UTC that is smoothed out. Since the smoothing process smooths out also frequency adjustments of the local clock, the leap smear is not exactly the same between different NTP servers.

When was the last time a leap second was added?

But Earth's slightly slower rotation means the two times are out of sync. To bridge the gap, leap seconds were introduced in 1972, and 27 have been added at irregular intervals since – the last in 2016.