Decade

== Usage ==
Any period of ten years is a "decade".<ref>{{Cite web| title = Decade| work = Lexico| access-date = 2020-02-26| date = 2020| url = https://www.lexico.com/definition/decade| archive-url = https://web.archive.org/web/20191230102633/https://www.lexico.com/definition/decade| url-status = dead| archive-date = December 30, 2019}}</ref> For example, the statement that "during his last decade, Mozart explored chromatic harmony to a degree rare at the time" merely refers to the last ten years of [[Wolfgang Amadeus Mozart]]'s life without regard to which calendar years are encompassed. Also, 'the first decade' of a person's life begins on the day of their birth and ends at the end of their 10th year of life when they have their 10th [[birthday]]; the second decade of life starts with their 11th year of life (during which one is typically still referred to as being "10") and ends at the end of their 20th year of life, on their 20th birthday; similarly, the third decade of life, when one is in one's twenties  or 20s, starts with the 21st year of life, and so on, with subsequent decades of life similarly described by referencing the tens digit of one's age. 

=== 0-to-9 decade ===
The most widely used method for denominating decades is to group years based on their shared tens digit, from a year ending in a 0 to a year ending in a 9{{snd}} for example, the period from 1960 to 1969 is the 1960s, and the period from 1970 to 1979 is the 1970s. Sometimes, only the tens part is mentioned (''{{`}}60s'' or ''sixties'', and ''{{`}}70s'' or ''seventies''), although this may leave it ambiguous as to which [[century]] is meant. However, this method of grouping decades cannot be applied to the decade immediately preceding AD{{nbs}}10, because there was no year 0.

Referring to ten-year periods as decades in this way only became common in the late 19th century.<ref>{{cite web|url=https://learningenglish.voanews.com/a/a-23-2010-01-20-voa1-84659222/117631.html|title=Now We're Past the, Uh, First Decade, What Do We Call the Next One|publisher=Learning English|language=English|date=20 January 2010|accessdate=2 January 2022}}</ref> Particularly in the 20th century, ''0-to-9'' decades came to be referred to with associated nicknames, such as the "[[Roaring Twenties]]" ([[1920s]]), the "Warring Forties" ([[1940s]]), and the "[[Swinging Sixties]]" ([[1960s]]). This practice is occasionally also applied to decades of earlier centuries; for example, referencing the [[1890s]] as the "[[Gay Nineties]]" or "Naughty Nineties".

=== 1-to-0 decade ===
A rarer approach groups years from the beginning of the [[Anno Domini|AD calendar era]] to produce successive decades from a year ending in a 1 to a year ending in a 0, with the years 1–10 described as "the 1st decade", years 11–20 "the 2nd decade", and so on; later decades are more usually described as 'the st, nd, rd, or th decade of the st, nd, rd, or th century' (using the [[century|strict interpretation of 'century']]).{{efn| name = century}} For example, "the second decad of the 12th. Cent." {{sic}};<ref>{{cite book |last1=1837 HALLAM Hist. Lit. I. i. 19 |title=The Compact Edition of the Oxford English Dictionary }}</ref> "The last decade of that century";<ref>{{cite book |last1=1878 DOWDEN Stud. Lit. I |title=The Compact Edition of the Oxford English Dictionary }}</ref> "1st decade of the 16th century";<ref>{{cite web |title=Catalogue of Illuminated Manuscripts |url=https://www.bl.uk/catalogues/illuminatedmanuscripts/results.asp?AttribID=228 |website=British Library |access-date=24 February 2020 |archive-date=29 June 2022 |archive-url=https://web.archive.org/web/20220629043437/https://www.bl.uk/catalogues/illuminatedmanuscripts/results.asp?AttribID=228 |url-status=dead }}</ref> "third decade of the 16th century";<ref>{{cite web |title=Illuminated Manuscripts from the Collection of Maurice Burrus (1882–1959) |url=https://www.christies.com/lotfinder/Lot/book-of-hours-use-of-paris-in-5994394-details.aspx |website=CHRISTIE'S |access-date=24 February 2020}}</ref> "the first decade of the 18th century".<ref>{{cite web |title=French harpsichord music in the first decade of the 18th century |url=https://academic.oup.com/em/article-abstract/XVII/2/184/352150?redirectedFrom=PDF |website=Oxford Academic |access-date=24 February 2020}}</ref> This decade grouping may also be identified explicitly; for example, "1961–1970";<ref>{{cite web |title=Past Poets Laureate: 1961–1970 |url=https://www.loc.gov/poetry/laureate-1961-1970.html |website=The Library of Congress |access-date=24 February 2020}}</ref> "2001–2010";<ref>{{cite web |title=Milestones 2001–2010 |url=https://www.un.org/en/sections/history/milestones-2001-2010/index.html |website=United Nations |access-date=24 February 2020}}</ref> "2021–2030".<ref>{{cite web |title=Solar Eclipses: 2021–2030 |url=https://eclipse.gsfc.nasa.gov/SEdecade/SEdecade2021.html |website=NASA |access-date=24 February 2020}}</ref> The BC calendar era ended with the year 1{{nbs}}BC and the AD calendar era began the following year, AD{{nbs}}1. There was no year 0.

{| class="wikitable"
|+ Usage methods compared
!Year
|1
|2
|3
|...
|9
|10
|11
|12
|...
|19
|20
|...
|2000
|2001
|2002
|...
|2009
|2010
|2011
|2012
|...
|2019
|2020
|2021
|2022
|...
|2029
|2030
|-
!0-to-9 decade
| colspan="5" style="background: #fef6e7; text-align: center;" |[[0s]]
| colspan="5" style="background: #fef6e7; text-align: center;" |[[10s]]
| colspan="2" style="text-align: center;" |...
| colspan="5" style="background: #fef6e7; text-align: center;" |[[2000s (decade)|2000s]]
| colspan="5" style="background: #fef6e7; text-align: center;" |[[2010s]]
| colspan="5" style="background: #fef6e7; text-align: center;" |[[2020s]]
| style="text-align: center;" |...
|-
!1-to-0 decade
| colspan="6" style="background: #eaeaff; text-align: center;" |1st decade of the 1st century
| colspan="5" style="background: #eaeaff; text-align: center;" |2nd decade of the 1st century
| colspan="2" style="text-align: center;" |...
| colspan="5" style="background: #eaeaff; text-align: center;" |1st decade of the 21st century
| colspan="5" style="background: #eaeaff; text-align: center;" |2nd decade of the 21st century
| colspan="5" style="background: #eaeaff; text-align: center;" |3rd decade of the 21st century
|}

=== Public usage of the two methods ===
A [[YouGov]] poll was conducted on December 2, 2019, asking 13,582 adults in the United States, "When do you think the next decade will begin and end?" Results showed that 64% answered that "the next decade" would begin on January 1, 2020, and end on December 31, 2029 (''0-to-9'' method); 17% answered that "the next decade" would begin on January 1, 2021, and end on December 31, 2030 (''1-to-0'' method); 19% replied that they did not know.<ref>{{cite web |title=In recent years, there has been debate around when a decade begins and ends. When do you think the next decade will begin and end? |url=https://today.yougov.com/topics/politics/survey-results/daily/2019/12/02/6529e/1 |website=YouGov |access-date=21 December 2019}}</ref>