Century#Start and end in the Gregorian calendar

Although a century can mean any arbitrary period of 100 years, there are two viewpoints on the nature of standard centuries. One is based on strict construction, while the other is based on popular perception.

According to the strict construction, the 1st century AD, which began with AD 1, ended with AD 100, and the 2nd century with AD 200;{{NoteTag|AD and CE year numbering, which are numerically equivalent, are now commonly used to number years, including those which occurred before these notations were invented; AD did not become widespread in Europe until early in the 2nd millennium.}} in this model, the n-th century starts with a year that follows a year with a multiple of 100 (except the first century as it began after the year 1 BC) and ends with the next coming year with a multiple of 100 (100n), i.e. the 20th century comprises the years 1901 to 2000, and the 21st century comprises the years 2001 to 2100 in strict usage.{{cite web |title=When Did the 21st Century Start? |url=https://www.timeanddate.com/counters/mil2000.html#:~:text=The%2021st%20Century%20Started%20in%202001&text=The%20year%20number%20in%20the,BC%2C%3A%20What's%20the%20difference%3F |website=timeanddate.com |access-date=23 November 2020}}

In common perception and practice, centuries are structured by grouping years based on sharing the 'hundreds' digit(s). In this model, the n-th century starts with the year that ends in "00" and ends with the year ending in "99";{{Cite web| title = century | work = Oxford Dictionaries| access-date = 20 January 2021| url = https://www.lexico.com/definition/century| archive-url = https://web.archive.org/web/20191230065254/https://www.lexico.com/definition/century| url-status = dead| archive-date = December 30, 2019}} for example, in popular culture, the years 1900 to 1999 constitute the 20th century, and the years 2000 to 2099 constitute the 21st century.{{Cite web| title = Centuries and How to Refer to Them | work = Merriam-Webster| access-date = 27 April 2021 | url = https://www.merriam-webster.com/words-at-play/centuries-and-how-to-refer-to-them}} (This is similar to the grouping of "0-to-9 decades" which share the 'tens' digit.)

To facilitate calendrical calculations by computer, the astronomical year numbering and ISO 8601 systems both contain a year zero, with the astronomical year 0 corresponding to the year 1 BC, the astronomical year -1 corresponding to 2 BC, and so on.{{Cite web| title = Calendars | work = L.E. Doggett| access-date = 27 April 2021| url = http://charon.nmsu.edu/~lhuber/leaphist.html | archive-url = https://web.archive.org/web/20120210184836/http://charon.nmsu.edu/~lhuber/leaphist.html | url-status = dead | archive-date = 10 February 2012 }}{{Cite web| title = Year Dating Conventions | work = National Aeronautics and Space Administration| access-date = 27 April 2021| url = https://eclipse.gsfc.nasa.gov/SEhelp/dates.html}}

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Informally, years may be referred to in groups based on the hundreds part of the year. In this system, the years 1900–1999 are referred to as the nineteen hundreds (1900s). Aside from English usage, this system is used in Swedish, Danish, Norwegian, Icelandic, Finnish and Hungarian. The Swedish {{Lang|sv|nittonhundratalet}} (or {{Lang|sv|1900-talet}}), Danish {{Lang|da|nittenhundredetallet}} (or {{Lang|da|nittenhundredetallet}}), Norwegian {{Lang|no|nittenhundretallet}} (or {{Lang|no|1900-tallet}}),{{Citation |last=Bolstad |first=Erik |title=århundre |date=2024-06-18 |work=Store norske leksikon |url=https://snl.no/%C3%A5rhundre |access-date=2025-04-06 |language=no}} Finnish {{Lang|fi|tuhatyhdeksänsataaluku}} (or {{Lang|fi|1900-luku}}) and Hungarian {{Lang|hu|ezerkilencszázas évek}} (or {{Lang|hu|1900-as évek}}) refer unambiguously to the years 1900–1999. In Swedish, however, a century is in more rare cases referred to as {{Lang|sv|det n-te seklet/århundradet}} ("the n-th century") rather than {{Lang|sv|n-hundratalet}}, i.e. the 17th century is (in rare cases) referred to as {{Lang|sv|17:(d)e/sjuttonde århundradet/seklet}} rather than 1600-talet and mainly also referring to the years 1601–1700 rather than 1600–1699;{{cite web | url=https://svenska.se/tre/?sok=sjuttonde&pz=1 | title=Sjuttonde | svenska.se }} according to Svenska Akademiens ordbok, {{Lang|sv|16:(d)e/sextonde århundradet}} may refer to either the years 1501–1600 or 1500–1599.{{cite web | url=https://svenska.se/tre/?sok=sextonde&pz=1 | title=Sextonde | svenska.se }}

While the century has been commonly used in the West, other cultures and calendars have utilized differently sized groups of years in a similar manner. The Hindu calendar, in particular, summarizes its years into groups of 60,{{cite web|title=www.vedavidyalaya.com|url=http://www.vedavidyalaya.com/varsham.htm|access-date=4 September 2013|archive-url=https://web.archive.org/web/20131217233346/http://www.vedavidyalaya.com/varsham.htm|archive-date=17 December 2013|url-status=dead}} while the Aztec calendar considers groups of 52.{{cite web|title=www.aztec-history.com|url=http://www.aztec-history.com/aztec-calendar.html|access-date=4 September 2013}}

{{Wiktionary|century}}

{{Commons category multi|Centuries|Centennials}}

• Age of Discovery
• Ancient history
• Before Christ and Anno Domini
• Common Era
• Decade
• List of decades, centuries, and millennia
• Lustrum
• Middle Ages
• Millennium
• Modern era
• Saeculum
• Year

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{{Reflist}}

• [ftp://ftp.loc.gov/pub/reference.guides/battle.centuries.txt The Battle of the Centuries]{{Dead link|date=October 2022 |bot=InternetArchiveBot |fix-attempted=yes }}, Ruth Freitag, U.S. Government Printing Office. Available from the Superintendent of Documents, P.O. Box 371954, Pittsburgh, PA 15250- 7954. Cite stock no. 030-001-00153-9. Retrieved 3 March 2019.

{{Time measurement and standards}}

Category:100 (number)

Category:Units of time