Generally speaking, a calendar year begins on the
New Year's Day
New Year's Day is a festival observed in most of the world on 1 January, the first day of the year in the modern Gregorian calendar. 1 January is also New Year's Day on the Julian calendar, but this is not the same day as the Gregorian one. Wh ...
of the given
calendar
A calendar is a system of organizing days. This is done by giving names to periods of time, typically days, weeks, months and years. A date is the designation of a single and specific day within such a system. A calendar is also a physi ...
system and ends on
the day before the following New Year's Day, and thus consists of a
whole number of days. A
year
A year or annus is the orbital period of a planetary body, for example, the Earth, moving in its orbit around the Sun. Due to the Earth's axial tilt, the course of a year sees the passing of the seasons, marked by change in weather, the hou ...
can also be measured by starting on any other named day of the calendar, and ending on the day before this named day in the following year.
This may be termed a "year's time", but not a "calendar year". To reconcile the calendar year with the
astronomical cycle (which has a fractional number of days) certain years contain
extra days ("leap days" or "intercalary days").
The
Gregorian year, which is in use in most of the world, begins on January 1 and ends on December 31. It has a length of 365 days in an
ordinary year, with 8760 hours, 525,600 minutes, or 31,536,000 seconds; but 366 days in a
leap year
A leap year (also known as an intercalary year or bissextile year) is a calendar year that contains an additional day (or, in the case of a lunisolar calendar, a month) added to keep the calendar year synchronized with the astronomical year or s ...
, with 8784 hours, 527,040 minutes, or 31,622,400 seconds. With 97 leap years every 400 years, the year has an average length of 365.2425 days. Other formula-based calendars can have lengths which are further out of step with the solar cycle: for example, the
Julian calendar
The Julian calendar, proposed by Roman consul Julius Caesar in 46 BC, was a reform of the Roman calendar. It took effect on , by edict. It was designed with the aid of Greek mathematicians and astronomers such as Sosigenes of Alexandr ...
has an average length of 365.25 days, and the
Hebrew calendar
The Hebrew calendar ( he, הַלּוּחַ הָעִבְרִי, translit=HaLuah HaIvri), also called the Jewish calendar, is a lunisolar calendar used today for Jewish religious observance, and as an official calendar of the state of Israel. I ...
has an average length of 365.2468 days. The
Islamic calendar
The Hijri calendar ( ar, ٱلتَّقْوِيم ٱلْهِجْرِيّ, translit=al-taqwīm al-hijrī), also known in English as the Muslim calendar and Islamic calendar, is a lunar calendar consisting of 12 lunar months in a year of 354 or ...
is a
lunar calendar
A lunar calendar is a calendar based on the monthly cycles of the Moon's phases (synodic months, lunations), in contrast to solar calendars, whose annual cycles are based only directly on the solar year. The most commonly used calendar, the Gre ...
consisting of 12
months in a year of 354 or 355 days.
Each Gregorian year has 179 even-numbered days; ordinary years have 186 odd-numbered days, but leap years have 187 odd-numbered days.
The astronomer's
mean tropical year
A tropical year or solar year (or tropical period) is the time that the Sun takes to return to the same position in the sky of a celestial body of the Solar System such as the Earth, completing a full cycle of seasons; for example, the time fro ...
, which is averaged over equinoxes and solstices, is currently 365.24219 days, slightly shorter than the average length of the year in most calendars, but the astronomer's value changes over time, so
John Herschel
Sir John Frederick William Herschel, 1st Baronet (; 7 March 1792 – 11 May 1871) was an English polymath active as a mathematician, astronomer, chemist, inventor, experimental photographer who invented the blueprint and did botanical wor ...
's suggested correction to the Gregorian calendar may become unnecessary by the year 4000.
Quarters
The calendar year can be divided into four quarters, often abbreviated as Q1, Q2, Q3, and Q4.
In the
Gregorian calendar
The Gregorian calendar is the calendar used in most parts of the world. It was introduced in October 1582 by Pope Gregory XIII as a modification of, and replacement for, the Julian calendar. The principal change was to space leap years dif ...
:
* First quarter, Q1: 1 January – 31 March (90 days or 91 days in leap years)
* Second quarter, Q2: 1 April – 30 June (91 days)
* Third quarter, Q3: 1 July – 30 September (92 days)
* Fourth quarter, Q4: 1 October – 31 December (92 days)
While in the
Chinese calendar
The traditional Chinese calendar (also known as the Agricultural Calendar 曆; 农历; ''Nónglì''; 'farming calendar' Former Calendar 曆; 旧历; ''Jiùlì'' Traditional Calendar 曆; 老历; ''Lǎolì'', is a lunisolar calendar ...
, the quarters are traditionally associated with the 4
season
A season is a division of the year based on changes in weather, ecology, and the number of daylight hours in a given region. On Earth, seasons are the result of the axial parallelism of Earth's tilted orbit around the Sun. In temperate and pol ...
s of the year:
*
Spring
Spring(s) may refer to:
Common uses
* Spring (season)
Spring, also known as springtime, is one of the four temperate seasons, succeeding winter and preceding summer. There are various technical definitions of spring, but local usage of ...
: 1st to 3rd month
*
Summer
Summer is the hottest of the four temperate seasons, occurring after spring and before autumn. At or centred on the summer solstice, the earliest sunrise and latest sunset occurs, daylight hours are longest and dark hours are shortest, wit ...
: 4th to 6th month
*
Autumn
Autumn, also known as fall in American English and Canadian English, is one of the four temperate seasons on Earth. Outside the tropics, autumn marks the transition from summer to winter, in September ( Northern Hemisphere) or March ( Sou ...
: 7th to 9th month
*
Winter
Winter is the coldest season of the year in polar and temperate climates. It occurs after autumn and before spring. The tilt of Earth's axis causes seasons; winter occurs when a hemisphere is oriented away from the Sun. Different cultures ...
: 10th to 12th month
See also
*
Academic term
An academic term (or simply term) is a portion of an academic year, the time during which an educational institution holds classes. The schedules adopted vary widely.
In most countries, the academic year begins in late summer or early autumn and ...
*
Calendar reform
Calendar reform or calendrical reform is any significant revision of a calendar system. The term sometimes is used instead for a proposal to switch to a different calendar design.
Principles
The prime objective of a calendar is to unambigu ...
*
Common year
A common year is a calendar year with 365 days, as distinguished from a leap year, which has 366. More generally, a common year is one without intercalation. The Gregorian calendar (like the earlier Julian calendar) employs both common years ...
*
Fiscal year
A fiscal year (or financial year, or sometimes budget year) is used in government accounting, which varies between countries, and for budget purposes. It is also used for financial reporting by businesses and other organizations. Laws in many ...
*
ISO 8601
ISO 8601 is an international standard covering the worldwide exchange and communication of date and time-related data. It is maintained by the Geneva-based International Organization for Standardization (ISO) and was first published in 1988, wi ...
*
ISO week date
The ISO week date system is effectively a leap week calendar system that is part of the ISO 8601 date and time standard issued by the International Organization for Standardization (ISO) since 1988 (last revised in 2019) and, before that, it was ...
*
Leap year
A leap year (also known as an intercalary year or bissextile year) is a calendar year that contains an additional day (or, in the case of a lunisolar calendar, a month) added to keep the calendar year synchronized with the astronomical year or s ...
*
Model year
The model year (sometimes abbreviated "MY") is a method of describing the version of a product which has been produced over multiple years. The model year may or may not be the same as the calendar year in which the product was manufactured.
...
*
Tropical year
A tropical year or solar year (or tropical period) is the time that the Sun takes to return to the same position in the sky of a celestial body of the Solar System such as the Earth, completing a full cycle of seasons; for example, the time fro ...
*
Seasonal year The seasonal year is the time between successive recurrences of a seasonal event such as the flooding of a river, the migration of a species of bird, or the flowering of a species of plant.
The need for farmers to predict seasonal events led to th ...
References
{{Reflist
Year
A year or annus is the orbital period of a planetary body, for example, the Earth, moving in its orbit around the Sun. Due to the Earth's axial tilt, the course of a year sees the passing of the seasons, marked by change in weather, the hou ...
Units of time
Types of year