((Short description|Transition to "New Style" dating system))
((pp|small=yes))
((Use dmy dates|date=September 2019))
[[File:Reforma Gregoriana del Calendario Juliano.jpg|thumb|
''Lunario Novo, Secondo la Nuova Riforma della Correttione del l'Anno Riformato da N.S. Gregorio XIII'', printed in [[Rome]] by Vincenzo Accolti in 1582, one of the first printed editions of the new calendar.]]

The '''adoption of the Gregorian Calendar''' was an event in the [[Human history#Early modern history|early modern history]] of most cultures and societies, marking a change from their traditional (or "old style") [[Calendar|dating system]] to the modern (or "new style") dating system((snd)) the [[Gregorian calendar]]((snd)) that is widely used around the world today. Some states adopted the new calendar from 1582, some did not do so before the early twentieth century, and others did so at various dates between. A few still have not, but except for these, the Gregorian calendar is now the world's [[civil calendar]] universally, although in many places an old style calendar remains used in religious or traditional contexts.<ref>[http://aa.usno.navy.mil/faq/docs/calendars.php Introduction to Calendars] ((Webarchive|url=https://web.archive.org/web/20190613115330/http://aa.usno.navy.mil/faq/docs/calendars.php |date=13 June 2019 )). [[United States Naval Observatory]]. Retrieved 15 January 2009.</ref><ref>[http://astro.nmsu.edu/~lhuber/leaphist.html Calendars] ((webarchive|url=https://web.archive.org/web/20040401234715/http://astro.nmsu.edu/~lhuber/leaphist.html |date=1 April 2004 )) by L. E. Doggett. Section 2.</ref>((efn|The international standard for the representation of dates and times, [[ISO 8601]], uses the Gregorian calendar. Section 3.2.1.)) During((snd)) and for some time after((snd)) the change between systems, it has been common to use the terms [[Old Style and New Style dates|"Old Style" and "New Style"]] when giving dates, to indicate which calendar was used to reckon them.

The [[Gregorian calendar]] was decreed in 1582 by the [[papal bull]] ((lang|la|[[Inter gravissimas]])) by [[Pope Gregory XIII]], to correct an error in the [[Julian calendar]] that was causing [[Gregorian calendar#Background|erroneous calculation]] of the date of [[Easter]]. The Julian calendar had been based upon a [[year]] lasting 365.25 [[day]]s, but this was slightly too long; in reality, it is about 365.2422 days,((efn|The average year in the Gregorian calendar is 365.2425 days.)) and so over the centuries, the calendar had drifted increasingly out of alignment with the Earth's orbit. According to Gregory's scientific advisers, the calendar had acquired ten excess [[leap day]]s since the [[First Council of Nicaea]] (which established [[Computus|the rule for dating Easter]] in AD 325). Consequently, he ruled, ten days must be skipped to restore the ((lang|la|[[status quo ante (phrase)|status quo ante]])): Catholic countries did this in 1582. Countries which did not change until the 18th century had by then observed an additional [[leap year]] (1700), necessitating the dropping of eleven days. Some countries did not change until the 19th or 20th century, necessitating one or two further days to be omitted from the calendar.

Although Gregory's reform was enacted in the most solemn of forms available to the [[Catholic Church|Church]], the bull had no authority beyond the Catholic Church and the [[Papal States]]. The changes he was proposing were changes to the civil calendar, over which he had no formal authority. They required adoption by the civil authorities in each country to have legal effect. The bull became the [[canon law]] of the Catholic Church in 1582, but it was not recognised by [[Protestantism|Protestant churches]], [[Eastern Orthodox Churches]], and a few others. Consequently, the days on which Easter (and related events in the [[Liturgical calendar]]) were celebrated by different Christian churches diverged.

==Adoption in Catholic countries==
[[Catholic Church|Catholic]] states such as [[Kingdom of France|France]], the [[History of Italy during foreign domination and the unification|Italian principalities]], [[Polish–Lithuanian Commonwealth|Poland–Lithuania]], [[Habsburg Spain|Spain]] (along with her European and overseas possessions), [[Iberian Union|Portugal]], and the Catholic states of the [[Holy Roman Empire]] were first to change to the Gregorian calendar. Thursday, 4 October 1582, was followed by Friday, 15 October 1582, with ten days skipped.

[[Philip II of Spain]] decreed the change from the Julian to the Gregorian calendar,<ref>((cite book |last=Kamen |first=Henry |date=1998 |title=Philip of Spain |url= https://books.google.com/books?id=wyWourPR5S8C&q=gregorian+calendar|publisher=Yale University Press |page=248 |isbn=0300078005))</ref> which affected much of Catholic Europe, as Philip was at the time ruler over [[Iberian Union|Spain and Portugal]] as well as [[History of Italy (1559–1814)|much of Italy]]. In these territories, as well as in the [[Polish–Lithuanian Commonwealth]] (ruled by [[Anna Jagiellon]]) and in the [[Papal States]], the new calendar was implemented on the date specified by the bull, with Julian Thursday, 4 October 1582, being followed by Gregorian Friday, 15 October 1582; the [[Spanish Empire|Spanish]] and [[Portuguese Empire|Portuguese colonies]] followed somewhat later ''de facto'' because of delay in communication.<ref>[http://hdl.loc.gov/loc.wdl/wdl.2837 ''"Pragmatica" on the Ten Days of the Year''] [[World Digital Library]], the first known South American imprint, produced in 1584 by Antonio Ricardo, of a four-page edict issued by King Philip II of Spain in 1582, decreeing the change from the Julian to the Gregorian calendar.</ref>

Other Catholic countries soon followed. [[Kingdom of France|France]] adopted the new calendar with Sunday, 9 December 1582, being followed by Monday, 20 December 1582.<ref>((cite web|url=http://norbyhus.dk/calendar.php#France |last=Nørby |first=Toke |title=The Perpetual Calendar: What about France? |date=29 February 2000 |access-date=15 June 2018))</ref>
The [[Dutch Republic|Dutch]] provinces of [[North Brabant|Brabant]] and [[Zeeland]], and the [[States General of the Netherlands|States General]] adopted it on 25 December of that year; the provinces forming the [[Southern Netherlands]] (modern [[Belgium]]) except the [[Duchy of Brabant]] adopted it on 1 January 1583; the province of [[Holland]] adopted it on 12 January 1583.((sfnp|Fruin|1934|p=10)) The seven Catholic [[Swiss canton]]s adopted the new calendar in January 1584.<ref name="Gutzwiller">((cite web|url=https://hls-dhs-dss.ch/fr/articles/012812/2018-01-15/|title=Calendriers|first=Hellmut Gutzwiller /|last=AB|website=HLS-DHS-DSS.CH))</ref>

==Adoption in Protestant countries==
Many [[Protestant]] countries initially objected to adopting a Catholic innovation; some Protestants feared the new calendar was part of a plot to return them to the Catholic fold.<ref>((cite journal |first=Gordon |last=Moyer |title=The Gregorian Calendar | journal=Scientific American |volume= 246 |number= 5 |date=May 1982 |pages=144–153 |jstor=24966597))</ref> In England for example, [[Elizabeth I of England|Queen Elizabeth I]] and her privy council had looked favourably to a Gregorian-like royal commission recommendation to drop 10 days from the calendar but the virulent opposition of the Anglican bishops, who argued that the Pope was undoubtedly [[Four kingdoms of Daniel|the fourth great beast of Daniel]], led the Queen to let the matter be quietly dropped.<ref>((cite journal| jstor=10.5325/j.ctv1c9hn8h |author-first1=F. J. |author-last1= Baumgartner | title=Popes, astrologers and Early modern calendar reform | journal= History Has Many Voices | editor= Lee Palmer Wandel | publisher = Pennsylvania State University Press | year=2003 | page= 176 | volume= 63|doi=10.5325/j.ctv1c9hn8h |isbn=9780271090931 ))</ref> In the [[Czech lands: 1526–1648|Czech lands]], Protestants resisted the calendar imposed by the [[Habsburg monarchy]]. In parts of Ireland, Catholic rebels (until their defeat in the [[Nine Years' War (Ireland)|Nine Years' War]]) kept the "new" Easter in defiance of the [[Kingdom of Ireland|English-loyal authorities]]; later, Catholics practising in secret petitioned the [[Propaganda Fide]] for [[dispensation (Catholic Church)|dispensation]] from observing the new calendar, as it signalled their disloyalty.<ref>
((cite web|url=https://ucc-ie.academia.edu/HiramMorgan/Papers/137094/The_Popes_new_invention_the_introduction_of_the_Gregorian_calendar_in_Ireland_1583-1782 |title='The Pope's new invention': the introduction of the Gregorian calendar in Ireland, 1583–1782 |first=Hiram |last=Morgan |format=[[Microsoft Word|MS Word]] |publisher="Ireland, Rome and the Holy See: History, Culture and Contact", a [[University College Cork|UCC]] History Department [[symposium]] |location=[[Pontifical Irish College]], Rome |date=1 April 2006 |access-date=17 October 2010 |url-status=dead |archive-url=https://web.archive.org/web/20110719134353/http://ucc-ie.academia.edu/HiramMorgan/Papers/137094/The_Popes_new_invention_the_introduction_of_the_Gregorian_calendar_in_Ireland_1583-1782 |archive-date=19 July 2011 ))
</ref>

===Prussia===
The Lutheran [[Duchy of Prussia]], until 1657 still a [[fiefdom]] of Catholic Poland, was the first Protestant state to adopt the Gregorian calendar. Under the influence of its liege lord, the King of Poland, it agreed in 1611 to do so.((citation needed|date=October 2018)) So 22 August was followed by 2 September 1612.((citation needed|date=October 2018)) However, this calendar change did not apply to other territories of the [[Hohenzollern]], such as Berlin-based [[Brandenburg]], a fief of the Holy Roman Empire.

===Denmark and Norway===
In 1700, through [[Ole Rømer]]'s influence, [[Denmark–Norway]] adopted the solar portion of the Gregorian calendar simultaneously with the [[March of Brandenburg|Brandenburg-Pomerania]] and other Protestant estates of the Holy Roman Empire. Sunday, 18 February 1700, was followed by Monday, 1 March 1700.<ref name="NT-Perpetual-Calendar">Nørby, Toke. [http://www.norbyhus.dk/calendar.php The Perpetual Calendar]</ref> None of these states adopted the [[Computus|lunar portion]], instead calculating the date of Easter astronomically using the instant of the vernal equinox and the full moon according to [[Johannes Kepler|Kepler]]'s ''[[Rudolphine Tables]]'' of 1627; this combination was referred to by the Protestant estates as the "improved calendar" (''Verbesserte Kalender'') and considered to be distinct from the Gregorian. They finally adopted the Gregorian calculation of Easter in 1774.<ref>((cite journal|url=http://adsabs.harvard.edu/full/1920PA.....28...18L|last=Lamont|first=R|title=The Reform of the Julian Calendar|journal=Popular Astronomy|volume=28|number=6|page=22|date=1920|bibcode=1920PA.....28...18L))</ref>

===Rest of the Dutch Republic===
The remaining provinces of the [[Dutch Republic]] adopted the Gregorian calendar on 12 July 1700 (Gelderland), 12 December 1700 (Overijssel and Utrecht), 12 January 1701 (Friesland and Groningen) and 12 May 1701 (Drenthe).((sfnp|Fruin|1934|pp=10–11))

===Sweden===
((Further|Swedish calendar))
[[File:Almanacka 1753.jpg|thumb|Swedish ''[[Almanach]]'' of 1753]]

Sweden's transition to the Gregorian calendar was difficult and protracted. Sweden started to make the change from the Julian calendar and towards the Gregorian calendar in 1700, but it was decided to make the (then 11-day) adjustment gradually by excluding the leap days (29 February) from each of 11 successive leap years, 1700 to 1740. Meanwhile, the Swedish calendar would be out of step with both the Julian calendar and the Gregorian calendar for 40 years; also, the difference would not be constant but would change every four years. This system had the potential for confusion when working out the dates of Swedish events in this 40-year period. To add to the confusion, the system was poorly administered, and the leap days that should have been excluded in 1704 and 1708 were not excluded. The Swedish calendar (according to the transition plan) should have been 8 days behind the Gregorian but was 10 days behind. King [[Charles XII of Sweden|Charles XII]] recognised that the gradual change to the new system was not working, and he abandoned it.

Rather than proceeding directly to the Gregorian calendar, it was decided to revert to the Julian calendar. This was achieved by introducing [[30 February|the unique date 30 February]] in 1712, adjusting the discrepancy in the calendars from 10 back to 11 days. Sweden finally adopted the solar portion of the Gregorian calendar in 1753, when Wednesday, 17 February, was followed by Thursday, 1 March. What became later [[Finland]] was an integral part of the [[Swedish kingdom#Swedish Empire|Swedish kingdom]] at that time, hence it did the same.<ref name=MS>Mike Spathaky, [http://www.cree.name/genuki/dates.htm "Old Style and New Style Dates and the change to the Gregorian Calendar: A summary for genealogists"]</ref> The Russian Empire's 1809 [[Finnish War|conquest]] of [[Finland]] did not revert this, since autonomy was granted, but government documents in Finland were dated in both the Julian and Gregorian styles. This practice ended when independence was gained in 1917.

===Great Britain and its colonies===
((main article|Old Style and New Style dates))
[[File:William Hogarth 028.jpg|thumb|[[William Hogarth]] painting: ''[[Humours of an Election]]'' (''c.'' 1755), which is the main source for the [[Calendar (New Style) Act 1750#Reaction and effect|"Give us our Eleven Days" mythical riots.]]]]
Through enactment of the [[Calendar (New Style) Act 1750]], [[Kingdom of Great Britain|Great Britain]] and [[British Empire|its possessions]] (including parts of what is now the United States) adopted the Gregorian calendar in 1752, by which time it was necessary to correct by 11 days. Wednesday, 2 September 1752, was followed by Thursday, 14 September 1752. In Great Britain, the term "New Style" was used for the calendar and the Act omits any acknowledgement of Pope Gregory: the Annexe to the Act established a [[computus|computation for the date of Easter]] that achieved the same result as Gregory's rules, without actually referring to him.<ref>((cite web| url=https://www.legislation.gov.uk/apgb/Geo2/24/23/1991-02-01?timeline=false | title= Calendar (New Style) Act 1750 ((!)) Chapter 23 24 Geo 2 | publisher = Parliament of Great Britain))</ref>

With the same Act, the Empire (except Scotland, which had already done so from 1600) changed the start of the civil year from 25 March to 1 January. Consequently, the custom of [[dual dating]] (giving a date in both old and new styles) can refer to the Julian/Gregorian calendar change, or to the start of year change, or to both.

===Adoption in the Americas===
The European colonies of [[the Americas]] adopted the change when their mother countries did. [[New France]] and [[New Spain]] had adopted the new calendar in 1582. The Gregorian calendar was applied in the British colonies in Canada and the future United States east of the [[Appalachian Mountains]] in 1752.

==== Alaska ====
[[Alaska]] remained on the Julian calendar along with the rest of Russia until 1867, when it was [[Alaska Purchase|sold to the United States]]. At noon on Saturday, 7 October 1867 (Julian), the date changed to Friday, 18 October 1867 (Gregorian). Although the Julian calendar was 12 days behind the Gregorian calendar, only 11 days were skipped because Alaska also moved from the Eurasian side of the [[International Date Line]] to the American side.((sfnp|Sumner|1875|p=348))

===Rest of Switzerland===
As noted above, the Catholic cantons of Switzerland adopted the new calendar in 1582. [[Geneva]] and several Protestant cantons adopted it in January 1701 or at other dates throughout the 18th century. The two [[Municipalities of Switzerland|Swiss communes]] of [[Schiers]] and [[Grüsch]] were the last areas of Western and Central Europe to switch to the Gregorian calendar, in 1812.<ref name="Gutzwiller" />

==Adoption in Eastern Europe==
Many of the countries of [[eastern Europe]] were [[Eastern Orthodox]] or [[Islam]]ic and adopted the Gregorian calendar much later than [[western Christian]] countries. Catholic countries such as the [[Polish–Lithuanian Commonwealth]] adopted the "new style" (N.S.) Gregorian calendar in 1582 (switched back in 1795 after the [[Third Partition of Poland]]), but the switch to the Gregorian calendar for secular use occurred in [[Eastern Orthodox]] countries as late as the 20th century((snd)) and some religious groups in some of these countries still use the "old style" (O.S.) Julian calendar for ecclesiastical purposes.

The [[Kingdom of Bulgaria]] changed from the Julian to the Gregorian calendar in 1916 during the [[First World War]]. 31 March was followed by 14 April 1916.<ref>See ((Citation |contribution = Закон за въвеждане на Грегориянския календар [Law on Introduction of the Gregorian Calendar] |title = Държавен вестник [Durzhaven Vestnik (State Gazette)]|volume=XXXVII |location= Sofia |date= 21 March 1916 |publisher=Government of Bulgaria)).</ref>

The [[Ottoman Empire]]'s [[Rumi calendar]], used for fiscal purposes, was realigned from a Julian to a Gregorian starting on 16 February / 1 March 1917. The beginning of the year was reset to 1 January starting in 1918. The numbering of the years, though, remained uniquely Turkish until the Gregorian calendar was introduced for general purposes on 1 January 1926.((efn|See discussion and references at [[Rumi calendar]].))

=== Russia ===
((Main|Soviet calendar))
[[File:Sovnarkom-Gregorian-Calendar-Decree-izo39.jpg|thumb|upright|Partial Russian text of the decree adopting the Gregorian calendar in Russia as published in ''[[Pravda]]'' on 25 January 1918 (Julian) or 7 February 1918 (Gregorian). It instructed citizens to count the day after January 31 as 14th February.]]
In [[Russia]], the Gregorian calendar was accepted after the [[October Revolution]]. On 24 January 1918, the [[Sovnarkom|Council of People's Commissars]] issued a [[Soviet Decrees|decree]] that Wednesday, 31 January 1918, was to be followed by Thursday, 14 February 1918, thus dropping 13 days from the calendar. With the change, the October Revolution itself, once converted, took place on 7 November. Articles about the October Revolution that mention this date difference tend to do a full conversion to the dates from Julian to the Gregorian calendar. For example, in the article "The October (November) Revolution" the ''[[Encyclopædia Britannica]]'' uses the format of "25 October (7 November, New Style)" to describe the date of the start of the revolution.<ref>((cite web|url=http://www.britannica.com/eb/article-38556/Russia |title=Russia: The October (November) Revolution |publisher=Encyclopædia Britannica Online |year=2007 |access-date=18 March 2007))</ref>

===Ukraine===
In the territory of modern [[Ukraine]], the Gregorian calendar was officially adopted for secular use immediately after its adoption by Pope Gregory XIII in 1582, as most of Ukraine then was part of the predominantly Catholic [[Polish-Lithuanian Commonwealth]]. The [[Roman Catholic Church in Ukraine]] switched to the new calendar at the same time. However, the Orthodox churches in the Commonwealth refused to accept a calendar instigated by a Roman Catholic Pope, so the [[Orthodox Church of Ukraine]] continued to follow to the old Julian calendar until 2023.

In 2018, the [[Ukrainian Lutheran Church]] switched to the [[Revised Julian calendar]]. After the Russian invasion in 2022, most other Christian denominations that were still using the old Julian calendar announced that they would transition to the Gregorian or the Revised Julian calendar. The [[All-Ukrainian Union of Churches of Evangelical Christian Baptists]] and the Church of Christians of the Evangelical Faith of Ukraine ([[Pentecostals]]) switched to the Gregorian calendar the same year. On 1 September 2023, the [[Ukrainian Greek Catholic Church]] switched to the Gregorian calendar, while the Orthodox Church of Ukraine opted for the Revised Julian calendar. At the same time, the [[Ukrainian Orthodox Church (Moscow Patriarchate)]] declared that it would continue to celebrate the birth of Christ according to the Julian calendar.

=== Others ===
Other countries of Eastern Europe, most notably [[Eastern Orthodox]] countries, adopted the Gregorian calendar for secular purposes in the 1910s or early 1920s. By the 20th century, the date on the Julian calendar was 13 days behind that on the Gregorian calendar. [[Romania]] adopted the Gregorian in 1919, with 31 March 1919 being followed by 14 April 1919.

The last country of Eastern Orthodox Europe to adopt the Gregorian calendar for secular purposes was Greece, at the time under military administration following the [[11 September 1922 Revolution]]. The date of change was 1 March 1923, As a consequence, Wednesday 15 February 1923 in the Greek calendar was followed by Thursday 1 March 1923.<ref name="NT-Perpetual-Calendar" /><ref>((cite journal |last1=Theodossiou |first1=E. Th. |last2=Manimanis |first2=V. N. |last3=Mantarakis |first3=P. |date=2007 |title=Demetrios Eginitis: Restorer of the Athens Observatory |journal=Journal of Astronomical History and Heritage |volume=10 |issue=2 |pages=123–132 |doi=10.3724/SP.J.1440-2807.2007.02.05 |bibcode=2007JAHH...10..123T|s2cid=129260817 ))</ref> The decree expressly limited the reform to lay (i.e. non-religious) matters, so the reform didn't affected the dates of religious holidays. (See below.)

[[Turkey]] adopted the Gregorian calendar on 1 January 1926.

===Non-adoption by Eastern Orthodox and Oriental Orthodox churches===
((See also|Coptic calendar|Ethiopian calendar|Old Calendarists))
While the civil administrations of Eastern European countries adopted the Gregorian calendar in the 1910s or early 1920s, none of the national [[Eastern Orthodox Churches]] have recognised the Gregorian calendar for church or religious purposes. Instead, the [[Revised Julian calendar]] was proposed in May 1923 at the [[Council of Constantinople (1923)|Council of Constantinople]]. It uses a different leap year rule, leading to the mean year being slightly shorter than that of the Gregorian calendar, while being constructed in such a way as to maximise the time before its dates start to diverge from the Gregorian. There will be no difference between the two calendars until 2800.

The [[Greek Orthodox Church of Jerusalem]], [[Russian Orthodox Church]], [[Serbian Orthodox Church]], [[Georgian Orthodox and Apostolic Church]], [[Polish Orthodox Church]], [[Macedonian Orthodox Church]] and the [[Greek Old Calendarists]] did not accept the Revised Julian calendar, and continue to celebrate Christmas on 25 December in the Julian calendar, which is 7 January in the Gregorian calendar until 2100.

All of the other Eastern churches, the [[Oriental Orthodoxy|Oriental Orthodox]] churches ([[Coptic Orthodox Church of Alexandria]], [[Ethiopian Orthodox Tewahedo Church]], [[Eritrean Orthodox Tewahdo Church]], and [[Syriac Orthodox Church]]) continue to use their own calendars, which usually result in fixed dates being celebrated in accordance with the Julian calendar. This is most interesting in the case of the Syriac Orthodox Church, as one of its Patriarchs, [[Ignatius Nemet Allah I]], was one of the nine scholars who devised the Gregorian calendar.((sfnp|Barsoum|2003)) The [[Indian Orthodox Church]] uses the Gregorian calendar along with their autonomous Syriac Orthodox counterparts in India, the [[Malankara Jacobite Syriac Orthodox Church]].

The [[Armenian Apostolic Church]] adopted the Gregorian calendar in 1923, except in the [[Armenian Patriarchate of Jerusalem]], where the old Julian calendar is still in use.<ref>[http://www.armenianchurch.net/worship/christmas/index.html ''The Armenian Church | Christmas''] ((Webarchive|url=https://web.archive.org/web/20100201210727/http://www.armenianchurch.net/worship/christmas/index.html |date=1 February 2010 )) (c. 2010). Diocese of the Armenian Church of America (Eastern).</ref><ref>Ardem A. Tajerian (n.d.). [http://www.churcharmenia.com/evangelical/evmain3_30_01b.html ''When Is Easter This Year?''] ((webarchive|url=https://web.archive.org/web/20120311000809/http://www.churcharmenia.com/evangelical/evmain3_30_01b.html |date=11 March 2012 )) CAKE Foundation. Retrieved 7 January 2009.</ref>

==Countries that used lunisolar calendars==
===Adoption in East Asia===
[[Meiji period|Japan]], [[Korean Empire|Korea]], and China started using the Gregorian calendar on ((nowrap|1 January 1873)), ((nowrap|1 January 1896)), and ((nowrap|1 January 1912)), respectively.<ref name="The Japanese Calendar History">((cite web|url=http://www.ndl.go.jp/koyomi/e/history/02_index2.html |title=The Japanese Calendar History |publisher=National Diet Library, Japan |year=2002 |access-date=19 March 2007 |archive-url=https://web.archive.org/web/20021203192541/http://www.ndl.go.jp/koyomi/e/history/02_index2.html |archive-date=3 December 2002 |url-status=dead |df=dmy-all))</ref><ref name="Andrei Lankov">((cite news|url=http://times.hankooki.com/lpage/opinion/200502/kt2005020616470454130.htm |archive-url=https://web.archive.org/web/20051217093140/http://times.hankooki.com/lpage/opinion/200502/kt2005020616470454130.htm |url-status=dead |archive-date=17 December 2005 |title=The Dawn of Modern Korea (266) Lunar Calendar |publisher=The Korea Times |first=Andrei |last=Lankov |date=6 February 2005 |access-date=27 August 2017))</ref>
They previously used [[lunisolar calendar]]s. The Old Style and New Style dates in these countries usually mean the older lunisolar dates and the newer Gregorian calendar dates respectively. In these countries, the old style calendars were similar but not all the same. The [[Arabic numerals]] may be used for both calendar dates in modern Japanese and Korean languages, but not for Chinese old-style dates.

====Japan====
Japan decided to officially replace [[Japanese calendar|its traditional lunisolar calendar]] with the Gregorian calendar in 1872, so the day following ((nowrap|31 December 1872)) as ((nihongo|"the second day of the twelfth month of Meiji 5"|明治5年12月2日|Meiji gonen jūnigatsu futsuka)) became ((nowrap|1 January 1873)),<ref name="The Japanese Calendar History"/> locally known as ((nihongo|"the first day of the first month of Meiji 6"|明治6年1月1日|Meiji rokunen ichigatsu tsuitachi)). (The Japanese rendering of the Western months is simply ''ichi-gatsu'' or "One-month" for January, ''ni-gatsu'' or "Two-month" for February, etc.<ref>((cite web|url=https://www.thoughtco.com/how-to-say-the-months-and-days-in-japanese-2028134|publisher=thoughtco.com|title=How to Say the Months, Days, and Seasons in Japanese|access-date=15 August 2019))</ref>) This brought Japan's calendar in alignment with that of the major Western powers (excluding Russia).

To this day, however, it is common to use [[Japanese era name|reign names]] (nengō), especially for official documents; for instance, ''[[Meiji period|Meiji]]'' 1 for 1868, ''[[Taishō period|Taishō]]'' 1 for 1912, ''[[Shōwa period|Shōwa]]'' 1 for 1926, ''[[Heisei period|Heisei]]'' 1 for 1989, ''[[Reiwa]]'' 1 for 2019, and so on. The months and days are those of the Gregorian calendar, but the year is either the "Western calendar" (西暦, ''seireki'') year number per the [[Common Era]] or [[Anno Domini]] system, or a year of the nengō of the emperor on the throne. Since 1873, an era and the first year of that era has begun on the day of the year that the emperor ascended the throne. The second year of that era began on the next 1 January even if the first year contained only a few days. All subsequent years of that era began on 1 January until that emperor died or abdicated. For example, the first year of the [[Showa Era]], that of Emperor [[Hirohito]], contained only the last six days of 1926, while Showa 64, his last year, contained only the first seven days of 1989. The current Gregorian year ((CURRENTYEAR)) corresponds to [[Reiwa]] ((#expr:((CURRENTYEAR))-2018)).

====Korea====
Replacing its years numbered from 1392, the founding of the [[Joseon]] dynasty,((sfnp|Lee|1996|page=[https://books.google.com/books?id=rhUm97beo2cC&pg=PA382 382]))((sfnp|Lee|1996|page=[https://books.google.com/books?id=rhUm97beo2cC&pg=PA520 p. 520 (note 13)])) [[Korea]] started using the Gregorian calendar on 1 January 1896, which was the 17th day of the 11th lunar month not only in Korea but also in [[Qing Dynasty|China]], which still used the lunisolar calendar.<ref name="Andrei Lankov"/> Yet [[Korean era name]]s were used for its years through 1910; and between 1910 and 1945, when [[Korea under Japanese rule|Korea was under Japanese rule]], [[Japanese era name]]s were used to count the years of the Gregorian calendar used in Korea.

In [[South Korea]], from 1945 until 1961, Gregorian calendar years were also counted from the foundation of [[Gojoseon]] in 2333 [[Before Christ|BC]] (regarded as year one), the date of the legendary founding of Korea by [[Dangun]], hence these Dangi (단기) years were 4278 to 4294. This numbering was informally used with the [[Korean calendar|Korean lunar calendar]] before 1945 but is only occasionally used today. Since 1997, [[North Korea]] officially counts years based on the [[North Korean calendar|Juche era]], the first year of which is 1912, the year of [[Kim Il Sung]]'s birth, with Gregorian months and days. The current Gregorian year ((CURRENTYEAR)) corresponds to Juche year ((#expr:((CURRENTYEAR))-1911)).

====China and Taiwan====
At its founding on ((nowrap|1 January 1912)), the [[Republic of China (1912–1949)|Republic of China]] (ROC) government under Provisional President [[Sun Yat-sen]] abolished the lunisolar [[Chinese calendar]] and adopted the Gregorian calendar. The public, however, resisted the change and continued to observe traditional holidays. President [[Yuan Shikai]] switched to a dual-calendar policy, under which the Gregorian calendar was to be used for most purposes except traditional holidays, which were to be timed according to the Chinese calendar; this would also be followed by the short-lived [[Empire of China (1915–1916)|Empire of China]].((efn|The [[s:zh:政府公報 (中華帝國)|Government Gazette of the Empire of China]] would be dated in the Gregorian calendar in the first year of [[Chinese era name|Hongxian]], i.e. 1916.)) With the [[Northeast Flag Replacement|1928 unification of China]] under the [[Kuomintang]], the [[Nationalist government]] decreed that, effective ((nowrap|1 January 1929)), the Gregorian calendar would be used. The [[Republic of China calendar]] would retain the Chinese traditions of numbering the months with a modified era system, determined according to the traditional [[Chinese era name]]s, but using the founding of the Republic of China government in 1912 as the start ([[epoch]]) rather than the [[regnal year]] of an emperor. The current Gregorian year ((CURRENTYEAR)) corresponds to the ROC year ((#expr:((CURRENTYEAR))-1911)). This system is still in use in [[Taiwan]] where the ROC government retains control [[Retrocession Day|since 1945]].

Upon its foundation in 1949, the [[People's Republic of China]] continued to use the Gregorian calendar with numbered months and adopted Western numbered years, but timed traditional holidays according to the Chinese calendar and abolished the ROC Era System. Today mainland China (including Hong Kong and Macau), Taiwan, Malaysia, Indonesia and Singapore all observe traditional holidays based on the traditional calendar, such as [[Chinese New Year]], while timing other holidays, especially national anniversaries, according to the Gregorian calendar. The adopted calendar in both mainland China and Taiwan is called the ''Public Calendar'' (((zh|s = 公历 |t = 公曆 |p = Gōnglì))), or "New Calendar" (((zh|s = 新历 |t = 新曆 |p = Xīnlì))).

The [[Chinese language]] may distinguish old and new style dates in different ways:

{| class="wikitable"
!Grammar
!Chinese calendar
!Gregorian calendar
|-
|Writing a date in Chinese characters
| ((Yes)) as the rule<ref name="ReferenceA">[[Guobiao standards|GB]]/T 15835-1995, ''General rules for writing numerals in publications'', Section 4.2.1</ref><ref>[[Guobiao standards|GB]]/T 33661-2017, ''Calculation and promulgation of the Chinese calendar'', Sections 6.2 and 6.3.1</ref>
| ((Yes)) as an option<ref name="ReferenceB">[[Guobiao standards|GB]]/T 15835-1995, ''General rules for writing numerals in publications'', Section 4.3</ref>
|-
|Writing a date in Arabic numerals
| ((No))((efn|Not supported by [[Guobiao standards|GB]]/T 15835-1995 or 33661-2017))((efn|In Taiwan, the [[Central Weather Bureau]] used to issue lunisolar calendars in Chinese characters through [https://web.archive.org/web/20160408172334/http://www.cwb.gov.tw/V7/astronomy/cdata/calpdf/2008cal.pdf 2008], but Arabic numerals from [https://web.archive.org/web/20160408173401/http://www.cwb.gov.tw/V7/astronomy/cdata/calpdf/2009cal.pdf 2009] to [https://web.archive.org/web/20160408173352/http://www.cwb.gov.tw/V7/astronomy/cdata/calpdf/2014cal.pdf 2014].))
| ((Yes)) as an option<ref name="ReferenceB"/>
|-
|Omitting 日 (rì, day) from a date
| ((Yes)) as an option<ref name="ReferenceA"/>
| ((No)), unless also omitting 月 (yuè, month), e.g. [[January 28 incident|一·二八]] (January 28) and [[December 9th Movement|一二·九]] (December 9)<ref>[[Guobiao standards|GB]]/T 15835-1995, ''General rules for writing numerals in publications'', Section 4.2.3</ref>
|-
|Prefixing 初 (chū, initial) for the first 10 days of a month<ref>The [[Ministry of Education Mandarin Chinese Dictionary]] defines [https://dict.revised.moe.edu.tw/dictView.jsp?ID=8548&q=1&word=初 初] as the adjective for the first ten days of a month of the Chinese calendar only.</ref>
| ((Yes)) as an option<ref name="ReferenceA"/><ref>[[Guobiao standards|GB]]/T 33661-2017, ''Calculation and promulgation of the Chinese calendar'', Section 6.3.1</ref>
| ((No))((efn|Not supported by [[Guobiao standards|GB]]/T 15835-1995))
|-
|正月 (zhēngyuè) as the first month<ref>The [[Ministry of Education Mandarin Chinese Dictionary]] defines [https://dict.revised.moe.edu.tw/dictView.jsp?ID=117236&q=1&word=正月 正月] as the first month of the Chinese calendar only.</ref>
| ((Yes))<ref>[[Guobiao standards|GB]]/T 33661-2017, ''Calculation and promulgation of the Chinese calendar'', Sections 3.22 and 6.2</ref>
| ((No))
|-
|元月 (yuányuè) or 一月 (yīyuè) as the first month<ref>The [[Ministry of Education Mandarin Chinese Dictionary]] defines [https://dict.revised.moe.edu.tw/dictView.jsp?ID=164963&word=元月 元月] as the first month of either the Chinese or Gregorian calendar.</ref>
| ((Yes)) as an option
| ((Yes))
|-
|冬月 (dōngyuè) as the eleventh month<ref>The [[Ministry of Education Mandarin Chinese Dictionary]] defines [https://dict.revised.moe.edu.tw/dictView.jsp?ID=48678&word=冬月 冬月] as the eleventh month of the Chinese calendar only.</ref>
| ((Yes)) as an option
| ((No)), write as month 11
|-
|臘月 (làyuè) as the twelfth month<ref>The [[Ministry of Education Mandarin Chinese Dictionary]] defines [https://dict.revised.moe.edu.tw/dictView.jsp?ID=59270&q=1&word=臘月 臘月] as the twelfth month of the Chinese calendar only.</ref>
| ((Yes)) as an option
| ((No)), write as month 12
|}

In speaking, people generally call the date in the Gregorian calendar month "No. ''dd''" (((zh |s = dd号 |t = dd號))); for example, the [[Chinese New Year|Spring Festival]] of year 2017 is No. 28 of Month 1 (((zh |s = 1月28号 |t = 1月28號))). On the other hand, people never call dates on the Chinese calendar as "No. ''dd".'', which avoids any possible ambiguity.

When referencing dates before the introduction of the Gregorian calendar in 1582, the official Chinese calendar may either inherit the issues with earlier calendars to be historically correct((efn|The [http://sinocal.sinica.edu.tw/ 2000-year converter of Chinese and Western calendars] by the [[Academia Sinica]] in Taiwan uses the [[Julian calendar]] from [[AD 1]] to ((nowrap|4 October 1582)) and allows users to customize the date of changing over from Julian to Gregorian calendar to suit [[List of adoption dates of the Gregorian calendar per country|specific needs]]. It uses Arabic numerals for both new and old style dates to ease programming, and considers [[AD 4]] a common year to correct the [[Julian calendar#Leap year error|leap year error]].)) or follow the [[proleptic Gregorian calendar]] if so specified.((efn|Simpler [http://www.programmer-club.com.tw/ShowSameTitleN/c/17411.html computer programming] may just treat 1 January 1 as Monday as in the proleptic Gregorian calendar, though historically incorrect.))

===Adoption in Southeast Asia===
((Main|Burmese calendar#Current status))

The Gregorian calendar replaced the [[Burmese calendar]] in several mainland Southeast Asian kingdoms in the second half of the 19th century. This took place in Cambodia in 1863 and Laos in 1889.<ref>((cite book |last1=Simms |first1=Peter |last2=Sanda |first2=Simms |date=2001 |title=The Kingdoms of Laos: Six Hundred Years of History |edition=illustrated |publisher=Psychology Press |isbn=9780700715312 |pages=204–210))</ref> In 1889, [[Siam]] also switched to the Gregorian calendar as the official civil calendar, with the [[Thai solar calendar#Rattanakosin Era|Rattanakosin Era]] (with 1782 as Year 1).<ref>((cite book |last=Smith |first=Ronald Bishop |date=1966 |title=Siam; Or, the History of the Thais: From 1569 A.D. to 1824 A.D. |volume= 2 |publisher= Decatur Press |page=11))</ref> The [[Thai lunar calendar]] remains in use for religious purposes. Since the British conquest of the [[Konbaung dynasty]] in 1886, the Gregorian calendar has been used alongside the Burmese calendar in [[Myanmar]].

==Islamic calendar==
The [[Islamic calendar]] is a lunar one so there are twelve [[lunar month]]s in a year of 354 or 355 days, being 11 days shorter than a [[Tropical year|solar year]]. Consequently, holy days in Islam migrate around the solar year on a 32-year cycle.<ref name=Economist171216 /> Some countries in the Islamic world use the Gregorian calendar for civil purposes, while retaining the Islamic calendar for religious purposes. For example, [[Saudi Arabia]] adopted the Gregorian calendar for the purpose of paying public sector staff effective 1 October 2016; private sector employers had already adopted the Gregorian calendar for pay purposes.<ref name=Economist171216>((cite news|url=https://www.economist.com/news/middle-east-and-africa/21711938-hauling-saudi-arabia-21st-century-saudi-arabia-adopts-gregorian|title=The prince's time machine: Saudi Arabia adopts the Gregorian calendar|newspaper=[[The Economist]]|date=17 December 2016))</ref><ref>((Cite web|url=https://www.independent.co.uk/news/world/middle-east/saudi-arabia-calendar-gregorian-switches-to-pay-workers-less-save-money-a7342331.html |archive-url=https://web.archive.org/web/20161003180054/http://www.independent.co.uk/news/world/middle-east/saudi-arabia-calendar-gregorian-switches-to-pay-workers-less-save-money-a7342331.html |archive-date=2016-10-03 |url-access=limited |url-status=live|title=Saudi Arabia has switched to a 'Western' calendar to save money|date=2016-10-03|website=The Independent|language=en|access-date=2019-12-07))</ref>

==Present situation==
((More citations needed section|date=December 2016))
((see also|Civil calendar))

Today, the vast majority of countries use the Gregorian calendar as their sole civil calendar. The four countries which have not adopted the Gregorian calendar are Ethiopia ([[Ethiopian calendar]]),<ref>"The Ethiopian Calendar", Appendix IV, C.F. Beckingham and G.W.B. Huntingford, ''The Prester John of the Indies'' (Cambridge: [[Hakluyt Society]], 1961)</ref> Nepal ([[Vikram Samvat]] and [[Nepal Sambat]]), Iran and Afghanistan ([[Solar Hijri calendar]]).<ref name="heydari">M. Heydari-Malayeri, [http://aramis.obspm.fr/~heydari/divers/ir-cal-eng.html A concise review of the Iranian calendar], Paris Observatory.</ref>

Some countries use other calendars alongside the Gregorian calendar, including India ([[Indian national calendar]]), Bangladesh ([[Bengali calendar]]), Pakistan ([[Islamic calendar]]), Israel ([[Hebrew calendar]]) and Myanmar ([[Burmese calendar]]), and other countries use a modified version of the Gregorian calendar, including Thailand ([[Thai solar calendar]]), Japan ([[Japanese calendar]]), North Korea ([[North Korean calendar]]) and Taiwan ([[Minguo calendar]]).

While many religious organizations reckon their [[liturgical year]] by the Gregorian civil calendar, others have retained their own calendars. [[List of calendars|Alternative calendars]] are used in many regions of the world today to mark cycles of religious and astrological events.

==Possible date conflicts==
The use of different calendars had the potential to cause confusion between contemporaries. For example, it is related<ref>((cite web |author=Lord Robertson |author-link=George Robertson, Baron Robertson of Port Ellen |title= Prospects for NATO–Russian relations |version= p. 1, para. 1 |publisher= NATO |year= 2000 |url= http://www.nato.int/docu/articles/2000/a000501a.pdf |format= .pdf|access-date= 19 March 2007))</ref> that one of the contributory factors for [[Napoleon I of France|Napoleon]]'s victory at the [[Battle of Austerlitz]] was the confusion between the Russians, who were using the Julian calendar, and the Austrians, who were using the Gregorian calendar, over the date that their forces should combine.<ref>((cite book |last=Chandler |first=David G |author-link=David G. Chandler |title=The Campaigns of Napoleon |publisher=Scribner |location=New York |date=1 March 1973 |page=[https://archive.org/details/campaignsofnapol00chan/page/383 383] |chapter=From the Rhine to the Danube |isbn=0-02-523660-1 |chapter-url-access=registration |chapter-url=https://archive.org/details/campaignsofnapol00chan/page/383 ))</ref> However, this tale is not supported in a contemporary account from a major-general of the Austrian Imperial and Royal Army, [[Karl Wilhelm von Stutterheim]], who tells of a joint advance of the Russian and Austrian forces (in which he himself took part) five days before the battle,<ref>((cite book|last=Stutterheim|first= Karl|translator-last=Pine-Coffin |translator-first=John |title=A Detailed Account of The Battle of Austerlitz|publisher= Goddard|year= 1807|location= London|page= [https://archive.org/details/bub_gb_KlNEAAAAIAAJ/page/n58 44]
|url= https://archive.org/details/bub_gb_KlNEAAAAIAAJ|quote=battle of austerlitz.))</ref> and it is explicitly rejected in Goetz's 2005 book-length study of the battle.<ref>((cite book |first=Robert |last=Goetz |title=1805: Austerlitz: Napoleon and the Destruction of the Third Coalition |publisher= Greenhill Books |date=2005 |oclc=1285476742 |url=https://archive.org/details/1805austerlitzna0000goet ))</ref>

==Timeline==
((main|List of adoption dates of the Gregorian calendar per country))

<timeline>
DateFormat = yyyy
ImageSize = width:800 height:auto barincrement:38
PlotArea = left:20 right:20 bottom:30 top:10
Colors =
 id:noir value:black
 id:canvas value:rgb(0.97,0.97,0.97)
 id:gris value:gray(0.80)
 id:grilleMajor value:rgb(0.80,0.80,0.80)
 id:bleuclair value:rgb(0.56,0.56,0.86)
 id:rouge value:red
 id:rougeclair value:rgb(0.86,0.56,0.56)
 id:bleuclair value:rgb(0.76,0.76,0.96)
 id:grilleMinor value:rgb(0.86,0.86,0.86)

Period = from:1550 till:2050
TimeAxis = orientation:horizontal format:yyyy
AlignBars = justify
ScaleMinor=unit:year increment:50 start:1550 gridcolor:grilleMinor
ScaleMajor=unit:year increment:100 start:1600 gridcolor:grilleMajor
BackgroundColors=canvas:canvas bars:canvas
BarData=
 bar:epoque
 barset:evennement

PlotData=
 bar:epoque shift:(0,0) width:30
 from:start till:end color:gris # Arri?re plan

 from:start till:1581 text:" Julian~ calendar" color:rougeclair anchor:from
 from:1582 till:end text:"Gregorian~ calendar" color:rouge
 barset:evennement color:noir shift:(2,0) width:25

 from:1582 till:1582 text:"1582~Spain, Portugal, and their possessions,~Italy, Polish-Lithuanian Commonwealth" shift:(2,5)
 from:1582 till:1582 text:"1582~France, Netherlands (Brabant, Zeeland and the Staten-Generaal), Savoy, Luxembourg"
 from:1582 till:1735 text:"1582 –1735~Duchy of Lorraine" color:bleuclair anchor:from
 from:1583 till:1583 text:"1583~Austria, Netherlands (Holland and modern Belgium), Catholic Switzerland and Germany"
 from:1584 till:1584 text:"1584~Bohemia and Moravia"
 from:1587 till:1587 text:"1587~Hungary"
 from:1605 till:1710 text:"1605 –1710~Nova Scotia" color:bleuclair anchor:from
 from:1610 till:1610 text:"1610~Duchy of Prussia"
 from:1648 till:1648 text:"1648~Alsace"
 from:1682 till:1682 text:"1682~Strasbourg"

 #To start again the indentation in top
 barset:break
 at:1700 #blank line
 at:1700 #blank line
 at:1700 #blank line
 at:1700 #blank line
 from:1700 till:1700 text:"1700~Protestant Germany, Netherlands (the northern provinces),~Switzerland, Denmark (incl. Norway, Iceland, and Faroe Islands)" shift:(2,5)
 from:1752 till:1752 text:"1752~Great Britain and its possessions"
 from:1753 till:1753 text:"1753~Sweden (incl. Finland)"
 from:1760 till:1760 text:"1760~Lorraine (Habsburg → France)"
 from:1811 till:1811 text:"1811~Swiss canton of Grisons"
 from:1867 till:1867 text:"1867~Alaska (Russia → USA)"
 from:1873 till:1873 text:"1873~Japan"
 from:1875 till:1875 text:"1875~Egypt"
 from:1889 till:1889 text:"1889~Siam (Thailand)"
 from:1896 till:1896 text:"1896~Korea"

 #To start again the indentation in top
 barset:break
 from:1912 till:1912 text:"1912~Albania"
 from:1912 till:1929 text:"1912 and 1929~China" color:bleuclair anchor:from
 from:1915 till:1915 text:"1915~Latvia, Lithuania"
 from:1916 till:1916 text:"1916~Bulgaria"
 from:1917 till:1917 text:"1917~Ottoman Empire"
 from:1918 till:1918 text:"1918~Russia, Estonia"
 from:1919 till:1919 text:"1919~Romania, Yugoslavia
 from:1923 till:1923 text:"1923~Greece"
 from:2016 till:2016 text:"2016~Saudi Arabia"

 #To start again the indentation in top
 barset:break

</timeline>

The date when each country adopted the Gregorian calendar, or an equivalent, is marked against a horizontal timeline. The vertical axis is used for expansion to show separate national names for ease in charting, but otherwise has no significance.

==Notes==
((notelist))

==References==

((reflist))

==Works cited==
((refbegin))
*((cite book |last1=Barsoum |first1=Ighnāṭyūs Afrām |editor-last=Moosa |editor-first=Matti |date=2003 |title=The scattered pearls : a history of Syriac literature and sciences |translator=Matti Moosa |others=with a foreword by Cyril Aphrem Karim. |publisher= Gorgias Press |location=Piscataway, NJ |isbn=9781931956048 |oclc=54405272))
*((cite book |last=Fruin |first=Robert |date=1934 |title=Handboek der Chronologie, voornamelijk van Nederland |trans-title=Handbook of Chronology, mainly from the Netherlands |language=nl |location=Alphen a/d Rijn |publisher=N. Samson |oclc=63421371|url=https://archive.org/details/HandboekDerChronologieFruin1934))
*((cite book |editor-last=Lee |editor-first=Peter H. |date=1996 |title=Sourcebook of Korean Civilization |volume=2: From the seventeenth century to the modern period |location=New York |publisher=Columbia University Press |isbn= 9780231079129 |oclc=26353271))
*((cite book |editor-last1=Lee |editor-first1=Peter H. |editor-last2=de Bary |editor-first2=W. T. |others= (with Yongho Ch'oe & Kang, H. H. W.) |date=2000 |title=Sources of Korean Tradition |volume=2 |location=New York |publisher=Columbia University Press |isbn=9780231120302 |oclc=278499245))
*((cite book |last=Sumner |first=Charles |date=1875 |page=[https://books.google.com/books?id=KawSAAAAYAAJ&pg=PA348 348] |title=The cession of Russian America to the United States |series=The Works of Charles Sumner |volume=11 |location=Boston |publisher=Lea and Shepard |url=https://archive.org/details/speechofhonchar00sumn/page/n1/mode/2up))
((refend))

==External links==
* [http://www.norbyhus.dk/calendar.php The Perpetual Calendar Gregorian Calendar adoption dates for many countries. ]
* [https://www.tondering.dk/claus/cal/gregorian.php What is the Gregorian calendar? with adoption dates for many countries and regions]

((Chronology))

[[Category:Gregorian calendar]]
[[Category:1582 in Christianity]]