Common year Common year A common year is a calendar year with 365 days. More generally, a common year is one without intercalation. The Gregorian calendar, (like the earlier Julian calendar), employs both common years and leap years to keep the calendar aligned with the tropical year, which does not contain an exact number of days. The common year of 365 days has 52 weeks and one day, hence a common year always begins and ends on the same day of the week (for example, January 1 and December 31 fell on a Sunday in 2017) and the year following a common
Leap year 25) fell on a Sunday in 2016, and Monday in 2017, then it will fall on Tuesday in 2018, and Wednesday in 2019 but then "leaps" over Thursday to fall on a Friday in 2020. The length of a day is also occasionally changed by the insertion of leap seconds into Coordinated Universal Time (UTC), owing to the variability of Earth's rotational period. Unlike leap days, leap seconds are not introduced on a regular schedule, since the variability in the length of the day is not entirely predictable. In the Gregorian calendar, the standard calendar in most of the world,