Dual dating is the practice, in historical materials, of indicating a date with what appear to be duplicate or excessive digits: these may be separated by a hyphen or a slash, or placed one above the other. The need for dual dating arose from the transition from an older calendar to a newer one. Another method used is to give the date of an event according to one calendar, followed in

parentheses A bracket is either of two tall fore- or back-facing punctuation marks commonly used to isolate a segment of text or data from its surroundings. They come in four main pairs of shapes, as given in the box to the right, which also gives their n ...

by the date of the same event in the other calendar, appending an indicator to each to specify which reference calendar applies. As an example, in the date "10/21February 1750/51" a style seen in the records of Great Britain and its possessions the notation arises from the prospective or previous adoption of the Gregorian calendar and a concurrent calendar reform. (The dual day number is due to the eleven days difference (at the time) between the

Julian calendar The Julian calendar is a solar calendar of 365 days in every year with an additional leap day every fourth year (without exception). The Julian calendar is still used as a religious calendar in parts of the Eastern Orthodox Church and in parts ...

date and the Gregorian one; the dual year is due to a change of start of year, from 25March to 1January.)

European countries and their colonies: Old Style and New Style dates

England, Wales, Scotland, Ireland and the American colonies

Long before the

British Empire The British Empire comprised the dominions, Crown colony, colonies, protectorates, League of Nations mandate, mandates, and other Dependent territory, territories ruled or administered by the United Kingdom and its predecessor states. It bega ...

adopted the Gregorian calendar, the date of the start of the year caused difficulties. Until 1752, England, Wales, Ireland and the American colonies started the legal year on 25March, whereas Scotland (since 1600), as well as common usage, started the year on 1January. This meant that a date such as 29January, while being toward the end of a legal year, would also be near the beginning of the following "common" (and Scottish) year. It was to show this duality that the system of displaying two year numbers first came into use examples may be seen on memorial tablets and in parish registers. Dating based on the year beginning on 25March became known as "Annunciation Style" dates, while dates of the year commencing on 1January were described as "Circumcision Style" dates, because this was the date of the

Feast of the Circumcision The Feast of the Circumcision of Christ is a Christian celebration of the circumcision of Jesus in accordance with Jewish tradition, eight days (according to the Semitic and southern European calculation of intervals of days) after his birth, th ...

, commemorating the eighth day of

Jesus Christ Jesus (AD 30 or 33), also referred to as Jesus Christ, Jesus of Nazareth, and many Names and titles of Jesus in the New Testament, other names and titles, was a 1st-century Jewish preacher and religious leader. He is the Jesus in Chris ...

's life after his birth, counted from its observation on

Christmas Day Christmas is an annual festival commemorating the birth of Jesus Christ, observed primarily on December 25 as a religious and cultural celebration among billions of people around the world. A liturgical feast central to Christianity, Chri ...

(25December). In 1752, England and its possessions changed the start of the year to 1January, and also adopted the

Gregorian calendar The Gregorian calendar is the calendar used in most parts of the world. It went into effect in October 1582 following the papal bull issued by Pope Gregory XIII, which introduced it as a modification of, and replacement for, the Julian cale ...

(on 2September). Thereafter, the terms "Old Style" (OS) and "New Style" (NS) were more commonly added to dates when it proved necessary or expedient to identify which calendar was being used for the given date. Often, both were given for example: 20January 1708(OS) (1709(NS)). There may be some confusion as to which calendar alteration OS or NS refers to: the change of the start of the year, or the transition of one style of calendar to another. Historically, OS referred only to the start of the year change, to 1January from 25March, and some historians still believe this is the best practice.J. R. Stockto
Date Miscellany I: The Old and New Styles
"The terms 'Old Style' and 'New Style' are now commonly used for both the 'Start of Year' and '

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) compared to a common year. The 366th day (or 13th month) is added to keep t ...

' changes (

England England is a Countries of the United Kingdom, country that is part of the United Kingdom. It is located on the island of Great Britain, of which it covers about 62%, and List of islands of England, more than 100 smaller adjacent islands. It ...

Wales Wales ( ) is a Countries of the United Kingdom, country that is part of the United Kingdom. It is bordered by the Irish Sea to the north and west, England to the England–Wales border, east, the Bristol Channel to the south, and the Celtic ...

: both in 1752;

Scotland Scotland is a Countries of the United Kingdom, country that is part of the United Kingdom. It contains nearly one-third of the United Kingdom's land area, consisting of the northern part of the island of Great Britain and more than 790 adjac ...

: 1600, 1752). I believe that, properly and historically, the 'Styles' really refer only to the 'Start of Year' change (from March 25 to January 1); and that the 'Leap Year' change should be described as the change from Julian to Gregorian."Death warrant of Charles I
web page of th
UK National Archives
A demonstration of New Style meaning Julian calendar with a start of year adjustment.Mike Spathak

"increasingly parish registers, in addition to a new year heading after 24 March showing, for example '1733', had another heading at the end of the following December indicating '1733/4'. This showed where the New Style 1734 started even though the Old Style 1733 continued until 24th March. However, OS and NS may refer to both alterations of the calendar:The October (November) Revolution

Encyclopædia Britannica The is a general knowledge, general-knowledge English-language encyclopaedia. It has been published by Encyclopædia Britannica, Inc. since 1768, although the company has changed ownership seven times. The 2010 version of the 15th edition, ...

, A demonstration of New Style meaning the Gregorian calendar. constructions like may be seen.

Rest of Europe

During the period between 1582, when the first countries adopted the Gregorian calendar, and 1923, when the last

Europe Europe is a continent located entirely in the Northern Hemisphere and mostly in the Eastern Hemisphere. It is bordered by the Arctic Ocean to the north, the Atlantic Ocean to the west, the Mediterranean Sea to the south, and Asia to the east ...

an country adopted it, it was often necessary to indicate the date of an event in both the

and the Gregorian calendar. Although the OS/NS notation was originally used only to clarify the date of events in the British Empire, the usage was reprised in more recent English-language histories of Russia, which retained the Julian calendar until 1918. For example, the beginning of the October Revolution may be recorded as 25October [ N.S. 7November] 1917 (or ).

East Asia

Meiji period, Japan,

Korea Korea is a peninsular region in East Asia consisting of the Korean Peninsula, Jeju Island, and smaller islands. Since the end of World War II in 1945, it has been politically Division of Korea, divided at or near the 38th parallel north, 3 ...

, and

China China, officially the People's Republic of China (PRC), is a country in East Asia. With population of China, a population exceeding 1.4 billion, it is the list of countries by population (United Nations), second-most populous country after ...

started using the Gregorian calendar on 1January 1873, 1896, and 1912, respectively. They had used

lunisolar calendar A lunisolar calendar is a calendar in many cultures, that combines monthly lunar cycles with the solar year. As with all calendars which divide the year into months, there is an additional requirement that the year have a whole number of mont ...

s previously. None of them used the Julian calendar; 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 The ten Arabic numerals (0, 1, 2, 3, 4, 5, 6, 7, 8, and 9) are the most commonly used symbols for writing numbers. The term often also implies a positional notation number with a decimal base, in particular when contrasted with Roman numera ...

may be used for both calendar dates in modern Japanese and Korean languages, but not in

Chinese language Chinese ( or ) is a group of languages spoken natively by the ethnic Han Chinese majority and List of ethnic groups in China, many minority ethnic groups in China, as well as by various communities of the Chinese diaspora. Approximately 1.39& ...

Japan

Japan started using the Gregorian calendar on 1January 1873, locally known as . The preceding day, 31December 1872, was . Japan currently employs two calendar systems: Gregorian and the

Japanese era name The or , is the first of the two elements that identify years in the Japanese era calendar scheme. The second element is a number which indicates the year number within the era (with the first year being "", meaning "origin, basis"), followed b ...

calendar. Specifically, the months and days now correspond to those of the Gregorian calendar, but the year is expressed as an offset of the era. For example, the Gregorian year 2007 corresponds to

Heisei The was the period of Japanese history corresponding to the reign of Emperor Akihito from 8 January 1989 until his abdication on 30 April 2019. The Heisei era started on 8 January 1989, the day after the death of the Emperor Hirohito, when hi ...

19. An era does not necessarily begin on 1January. For example, 7January Shōwa 64—the day of the death of Emperor Shōwa—was followed by 8January Heisei1, which lasted until 31December.

Korea

Korea started using the Gregorian calendar on 1January 1896, which was the 17th day of the 11th lunar month in not only Korea, but also in

that still used the lunisolar calendar. The lunisolar

Korean calendar Throughout its many years of history, various calendar systems have been used in Korea. Many of them were adopted from the Lunar calendar, lunar Chinese calendar system, with modifications occasionally made to accommodate Korea's geographic locat ...

is now used in very limited unofficial purposes only.

China

The

Republic of China Taiwan, officially the Republic of China (ROC), is a country in East Asia. The main geography of Taiwan, island of Taiwan, also known as ''Formosa'', lies between the East China Sea, East and South China Seas in the northwestern Pacific Ocea ...

(ROC) started using the Gregorian calendar on 1January 1912, but the lunisolar

Chinese calendar The traditional Chinese calendar, dating back to the Han dynasty, is a lunisolar calendar that blends solar, lunar, and other cycles for social and agricultural purposes. While modern China primarily uses the Gregorian calendar for officia ...

is still used along with the Gregorian calendar, especially when determining certain traditional holidays. The reference has been a longitude of 120°E since 1929, which is also used for Chinese Standard Time (

UTC+8 UTC+08:00 is an identifier for a time offset from UTC of +08:00. It is the most populous time zone in the world, as well as a possible candidate for ASEAN Common Time, mainly due to China's large population, with an estimated population ...

). Mainland China,

Hong Kong Hong Kong)., Legally Hong Kong, China in international treaties and organizations. is a special administrative region of China. With 7.5 million residents in a territory, Hong Kong is the fourth most densely populated region in the wor ...

Macau Macau or Macao is a special administrative regions of China, special administrative region of the People's Republic of China (PRC). With a population of about people and a land area of , it is the most List of countries and dependencies by p ...

Malaysia Malaysia is a country in Southeast Asia. Featuring the Tanjung Piai, southernmost point of continental Eurasia, it is a federation, federal constitutional monarchy consisting of States and federal territories of Malaysia, 13 states and thre ...

Indonesia Indonesia, officially the Republic of Indonesia, is a country in Southeast Asia and Oceania, between the Indian Ocean, Indian and Pacific Ocean, Pacific oceans. Comprising over List of islands of Indonesia, 17,000 islands, including Sumatra, ...

Singapore Singapore, officially the Republic of Singapore, is an island country and city-state in Southeast Asia. The country's territory comprises one main island, 63 satellite islands and islets, and one outlying islet. It is about one degree ...

and

Taiwan Taiwan, officially the Republic of China (ROC), is a country in East Asia. The main geography of Taiwan, island of Taiwan, also known as ''Formosa'', lies between the East China Sea, East and South China Seas in the northwestern Pacific Ocea ...

all have legal holidays based on the lunisolar Chinese calendar, with the most important one being the

Chinese New Year Chinese New Year, or the Spring Festival (see also #Names, § Names), is a festival that celebrates the beginning of a New Year, new year on the traditional lunisolar calendar, lunisolar Chinese calendar. It is one of the most important holi ...

. From 1995, to visually distinguish old and new style dates, writing new style dates with Arabic numerals but old style dates with

Chinese characters Chinese characters are logographs used Written Chinese, to write the Chinese languages and others from regions historically influenced by Chinese culture. Of the four independently invented writing systems accepted by scholars, they represe ...

(never Arabic numerals) was the standard in the People's Republic of China (PRC). Since 1November 2011, writing old style dates with Chinese characters, never Arabic numerals, remains the standard in the PRC, GB/T 15835-2011, ''General rules for writing numerals in publications'', Section 4.2.1 GB/T 33661-2017, ''Calculation and promulgation of the Chinese calendar'', Sections 6.2 and 6.3.1 but new style dates may be written with either Arabic or Chinese numerals. GB/T 15835-2011, ''General rules for writing numerals in publications'', Section 4.3 In Taiwan, even though new style dates are written in Chinese characters in very formal texts, it is now common to see Arabic numerals in new style dates in less formal texts. When writing old style dates, Chinese characters are usually used, but Arabic numerals may still be seen. The calendar year in Taiwan is usually expressed as the "Year of the Republic" — counting Year1 as the foundation of the Republic of China in 1912CE, so the current Gregorian year corresponds to the ROC year .

Use of dates from historical documents in modern documents

There was some confusion when calendars changed, and the confusion may continue today when evaluating historical sources. When 'translating' dates from secondary historical sources for current use, for dates in January, February and March it is advised that ''both'' year numbers be entered into modern documents until a copy of the original primary source can be checked, verifying which style was used in the 'official record'. Errors were often made in the early 19th century and have been perpetuated. In either case, to avoid further confusion, modern researchers are advised to be vigilant about annotating all dates with a notation indicating the Style of date, and to use a slash rather than a hyphen to indicate alternate dates.Mike Spathak
Old Style New Style dates and the change to the Gregorian calendar
"We as historians have no excuse for creating ambiguity and must keep to the notation described above in one of its forms ither using OS/NS to apply to the leap year correction, the start of the year correction, or both It is no good writing simply 20th January 1745, for a reader is left wondering whether we have used the Old or the New Style reckoning. The date should either be written 20th January 1745 OS (if indeed it was Old Style) or as 20th January 1745/6. The hyphen (1745-6) is best avoided as it can be interpreted as indicating a period of time."

References

Footnotes

{{DEFAULTSORT:Dual Dating Date and time representation