Nonleap

Nonleap refers to a calendar year that is not a leap year. A nonleap year contains 365 days, and February has 28 days. In the Gregorian calendar, most years are nonleap; a leap year with 366 days is added periodically to keep the calendar year aligned with the solar year.

In the Gregorian rule, a year is a leap year if it is divisible by 4, except that years divisible by 100 are not leap years unless they are also divisible by 400. This means that 1999, 2001, and 2019 are nonleap years, while 2000 and 2020 are leap years, and 1900 will be nonleap while 2000 was leap. Within a 400-year cycle, there are 303 nonleap years and 97 leap years.

The designation of a year as nonleap has practical implications for date calculations, scheduling, and the assignment of weekdays to dates. Over time, the repetition of weekdays for calendar dates can shift in nonleap years in relation to leap years, affecting annual calendars, fiscal planning, and timekeeping systems that do not otherwise account for leap days.

In common usage, nonleap is often referred to as a common year or ordinary year. The concept is also relevant in computing and date libraries, where software must handle the differing lengths of months and leap years when computing durations or validating dates.