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
Bissextus ecclesiastical calendars, the intercalary day is added for convenience at the end of the month of February, as February 29, and years in which February has twenty-nine days are called "bissextile," or leap years. Bissextus Bissext, or bissextus (Lat. "bis", twice; "sextus", sixth) is the day which is added to the Gregorian calendar every fourth year (except those evenly divisible by 100, unless they are divisible by 400) to compensate for the six-hour difference in length between the common 365-day year and the actual length of the solar year. Originally, the day was inserted after the 24th of February, i.e.