When was the last leap second added?
Quick Answer: The last leap second was added on December 31, 2016, at 23:59:60 UTC.
Leap seconds are added occasionally to keep our clocks in sync with Earth's slowing rotation. Since atomic clocks are extremely precise, leap seconds help adjust for tiny differences between atomic time and solar time.
The decision to add a leap second is made by the International Earth Rotation and Reference Systems Service (IERS). They announce these adjustments usually six months in advance, ensuring global timekeeping stays accurate for everything from GPS to internet networks.