Editing Calendar year

{{Short description|Period of time}}
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A '''calendar year''' begins on the [[New Year's Day]] of the given [[calendar]] system and ends on [[New Year's Eve|the day before]] the following New Year's Day, and thus consists of a [[natural number|whole number]] of days.

The [[Gregorian calendar]] year, which is in use as [[civil calendar]] in most of the world, begins on [[January 1]] and ends on [[December 31]].<ref>{{Cite news |title=calendar year |url=https://dictionary.cambridge.org/dictionary/english/calendar-year |archive-url=http://web.archive.org/web/20220503102342/http://dictionary.cambridge.org/dictionary/english/calendar-year |archive-date=2022-05-03 |access-date=2025-01-12 |work=[[Cambridge Dictionary]] |language=en}}</ref> It has a length of 365 days in an [[common year|ordinary year]] but, in order to reconcile the calendar year with the [[Year|astronomical cycle]], it has 366 days in a [[leap year]]. With 97 leap years every 400 years, the Gregorian calendar 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]] has an average length of 365.25 days, and the [[Hebrew calendar]] has an average length of 365.2468 days. The Lunar Hijri calendar ("[[Islamic calendar]]") is a [[lunar calendar]] consisting of 12 [[lunar month]]s in a year of 354 or 355 days.{{efn|The other Islamic calendar, observed in Iran, is the [[Solar Hijri calendar]]. It runs from spring equinox to spring equinox.}} The astronomer's [[mean tropical year]], which is averaged over equinoxes and solstices, is currently 365.24219 days, slightly shorter than the average length of the calendar year in most calendars.

A [[year]] 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.<ref>{{cite encyclopedia | url=http://www.merriam-webster.com/dictionary/calendar%20year | title=calendar year | dictionary=Merriam-Webster | access-date=6 August 2014}}</ref> This may be termed a "year's time", but is not a "calendar year".

==Quarter year==
{{anchor|Quarters}}
{{Redirect|Fourth quarter|the sports term|Comeback (sports)}}
The calendar year can be divided into four quarters,<ref>{{cite encyclopedia | url=https://www.merriam-webster.com/dictionary/calendar%20quarter |title=Calendar quarter |dictionary=Merriam-Webster (Merriam-Webster.com)|access-date= 23 December 2024}}</ref> often abbreviated as Q1, Q2, Q3, and Q4. Since they are three months each, they are also called [[Month|trimester]]s. In the [[Gregorian calendar]]:

* First quarter, Q1: January 1 – March 31 (90 days or 91 days in leap years)<ref>{{cite encyclopedia | url=https://dictionary.cambridge.org/us/dictionary/english/calendar-quarter |title=Calendar quarter |dictionary=Cambridge Business English Dictionary (Dictionary.Cambridge.org)|access-date= 23 December 2024}}</ref>
* Second quarter, Q2: April 1 – June 30 (91 days)
* Third quarter, Q3: July 1 – September 30 (92 days)
* Fourth quarter, Q4: October 1 – December 31 (92 days)

In some domains, weeks are preferred over months for scheduling and reporting, so they use quarters of exactly 13 weeks each, often following [[ISO week date]] conventions. One in five to six years has a 53rd week which is usually appended to the last quarter. It is then 98 days instead of 91 days long, which complicates comparisons.

In the [[Chinese calendar]], the quarters are traditionally associated with the 4 [[season]]s of the year:

* [[Spring (season)|Spring]]: 1st to 3rd month
* [[Summer]]: 4th to 6th month
* [[Autumn]]: 7th to 9th month
* [[Winter]]: 10th to 12th month

==Quadrimester==
The calendar year can also be divided into quadrimesters (from French ''quadrimestre''),<ref>{{cite encyclopedia | url=https://www.cnrtl.fr/definition/quadrimestre/ |title=QUADRIMESTRE : Définition de QUADRIMESTRE |dictionary=Centre National de Ressources Textuelles et Lexicales (cnrtl.fr)|access-date= 4 January 2025}}</ref> lasting for four months each. They can also be called the early, middle, or late parts of the year. In the [[Gregorian calendar]]:

* First quadrimester, early year: January 1 – April 30 (120 days or 121 days in leap years)
* Second quadrimester, mid-year: May 1 – August 31 (123 days)
* Third quadrimester, late year: September 1 – December 31 (122 days)

==Semester==
The calendar year can also be divided into semesters,<ref>{{cite encyclopedia | url=https://www.merriam-webster.com/dictionary/semester |title=Semester |dictionary=Merriam-Webster (Merriam-Webster.com)|access-date= 4 January 2025}}</ref> lasting six months each and often being abbreviated as S1 and S2. In the [[Gregorian calendar]]:

* First semester, S1: January 1 – June 30 (181 days or 182 days in leap years)
* Second semester, S2: July 1 – December 31 (184 days)

==See also==
{{Infobox calendar date today}}
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* {{Annotated link |Academic term}}
* {{anli|Bissextus}} (historical usage)
* {{Annotated link |Calendar reform}}
* {{Annotated link |Common year}}
* {{Annotated link |Fiscal year}}
* {{Annotated link |Intercalation (timekeeping)}}
* {{Annotated link |ISO 8601}}
* {{Annotated link |ISO week date}}
* {{anli|Julian date}}
* [[Julian year (astronomy)]]{{snd}} a time interval of exactly 365.25 Earth days
* [[Julian year (calendar)]]{{snd}} a year in the [[Julian calendar]] that is either 365 or 366 days, or 365.25 days on average
* {{Annotated link |Leap year}}
* {{Annotated link |Model year}}
* {{Annotated link |Ordinal date}}
* {{Annotated link |Seasonal year}}
{{div col end}}

==Notes==

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==References==
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[[Category:Calendars|Year]]
[[Category:Units of time]]
[[Category:Types of year]]