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Conversion of Julian to Gregorian dates
Time period (from March 1 of first year to February 29 of last year) Сorrection, days
400500 +1
500600 +2
600700 +3
700900 +4
9001000 +5
10001100 +6
11001300 +7
13001400 +8
14001500 +9
15001700 +10
17001800 +11
18001900 +12
19002100 +13

Old Style or OS is a designation indicating that a date conforms to the Julian calendar, formerly in use in many countries, rather than the Gregorian calendar, currently in use in most countries.

"Old Style" (OS) and "New Style" (NS) are sometimes added to dates to identify which system is used in the British Empire and other countries that did not immediately change to the Gregorian calendar. In Britain it is usual to map most dates from the Julian year onto the Gregorian year without converting the day and month. However because the start of the Julian year was not always January 1 (see New Year's Day section in the Julian calendar article), OS/NS is particularly relevant for dates which fall between the start of the Gregorian year (January 1), and the start of the Julian year which was March 25 in England. Great Britain did not adopt the Gregorian calendar until September 14, 1752 and it was not until that year that England officially adopted January 1 as the start of the calendar year.

For example, according to the English calendar of the day, King Charles I was executed on Tuesday January 30, 1648. This date is usually written in modern histories as January 30, 1649, showing merely the modernised end of year. In fact a full conversion of the date into the Gregorian calendar is February 9, 1649, the date by which his contemporaries in some parts of continental Europe would have recorded his execution.[1]

Possible date conflicts[]

For example, it is sometimes remarked that William Shakespeare and Miguel de Cervantes died on the same date, April 23, 1616, but not on the same day. England was still using the Julian calendar in 1616, while Spain was using the Gregorian calendar. Cervantes actually died ten days before Shakespeare.

Because of the differences, English people and their correspondents often employed two dates, more or less automatically, as Benjamin Woolley observed in his biography of Dr. John Dee, The Queen's Conjurer. Dee fought unsuccessfully for England to embrace the 1583/4 date set for the change. Woolley wrote because of "the decision, England remained outside the Gregorian system for a further 170 years, communications during that period customarily carrying two dates, one 'OS' or Old Style, the other 'NS' or New Style." (173) Thomas Jefferson, for example, lived during the time England eventually converted, so his tombstone bore his birthdate in the Old Style, and noted them as such, at his instruction. By then the difference was greater than ten days.

A further complication is that the start of the Julian year was not always January 1 but was altered at different times in different countries. For a long time the year in England began on March 25 (Lady Day), so for example Elizabeth I of England was recorded as having died on March 24, 1602 (Old Style); this would be written March 24, 1603 (New Style). Although this would correspond to April 3, 1603 if fully converted into the Gregorian calendar, the month and day of a British event are normally not converted. For complete avoidance of ambiguity, historians can write dates in the ambiguous part of the year in slashed format, e.g. "March 24/April 3, 1602/1603".

Catholic countries such as Italy, Poland, Spain, and Portugal were first to change to the Gregorian calendar. Thursday, October 4, 1582 was followed by Friday, October 15, 1582, with ten days "missing". Countries that did not change until the 1700s observed an additional leap year, necessitating eleven "missing days". Some countries did not change until the 1800s or 1900s, necessitating one or two more "missing days".

France changed from Julian to Gregorian Calendar on December 9, 1582 JU where the next day was December 20, 1582 GR. France used the French Republican Calendar from September 22, 1792 GR to December 31, 1805 GR.

File:Marriage certificate-1907.jpg

Marriage certificate showing Old- and New-Style dates, Warsaw 1907.[2]

In Russia, the terms "Old Style" and "New Style" have the same significance as elsewhere. The start of the year was moved to January 1 in 1700, but the Gregorian calendar was introduced there much later, already in the Russian SFSR — on February 14, 1918 (Gregorian calendar). Hence the October Revolution of 1917 is so called, despite having started on November 7 under the Gregorian calendar (October 25 [Julian calendar]). Articles about the October Revolution which mention this date difference tend to do a full conversion to the dates from Julian to the Gregorian calendar. For example the article "The October (November) Revolution" the Encyclopædia Britannica uses the format of "October 25 (November 7, New Style);" to describe the date of the start of the revolution.[3]

Occasionally using different calendars has caused confusion between contemporaries. For example one of the contributory factors for 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.[4]

The mapping of new dates onto old dates with a start of year adjustment works well with little confusion for events which happened before the introduction of the Gregorian Calendar on December 9, 1582 (in France). For example the Battle of Agincourt is universally known to have been fought on October 25, 1415, which is Saint Crispin's Day. But for the period between the first introduction of the Gregorian calendar October 4, 1582 and its introduction in Britain on September 14, 1752, there can be considerable confusion between events in continental western Europe and in British domains. Events in continental western Europe are usually reported in English language histories as happening under the Gregorian calendar. For example the Battle of Blenheim is always given as August 13, 1704. However confusion occurs when an event affects both. For example William III of England arrived at Brixham in England on November 5 (Julian calendar), after setting sail from the Netherlands on November 11 (Gregorian calendar). To add to the confusion, the Battle of Boyne, which took place only a few months later in Ireland on July 1 "Old Style", is not mapped to July 1 "New Style" but is remembered as taking place on July 12. The keeping of the recorded date (not a mapped date) for the anniversary of this battle has more to do with Protestants not at first recognising Gregorian dates, so they continued to celebrate the anniversary on their Protestant July 1 and now traditionally do so.

Countries that used lunisolar calendars[]

Japan, Korea, and China started using the Gregorian calendar on January 1 of 1873, 1896, and 1912, respectively.[5] They used lunisolar calendars previously. In these countries, the old style calendars were similar but not all the same. 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. Arabic numerals may be used for both calendar dates in modern Japanese and Korean languages, but not Chinese.


Japan started using the Gregorian calendar on January 1, 1873,[6] locally known as "the first day of the first month of Meiji 6" (明治6年1月1日). The preceding day, December 31, 1872, was "the second day of the twelfth month of Meiji 5" (明治5年12月2日).

The lunisolar Japanese calendar is no longer used except in very limited unofficial purposes, in which case 135° E of longitude is the modern reference point also used for Japan Standard Time (UTC+9), as opposed to Kyoto as the ancient reference point and the national capital until 1868.


Korea started using the Gregorian calendar on January 1, 1896, which was the 17th day of the 11th lunar month in not only Korea but also in China that still used the lunisolar calendar.[7] The lunisolar Korean calendar is now used in very limited unofficial purposes only.


The Republic of China started using the Gregorian calendar on January 1, 1912, but the lunisolar Chinese calendar 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). China, Hong Kong, Macao, Singapore and Taiwan all have legal holidays based on the lunisolar Chinese calendar, with the most important one being the Chinese New Year.

To visually distinguish old and new style dates, GB/T 15835-1995, General rules for writing numerals in publications, which is a national standard of the People's Republic of China, requires writing new style dates with Arabic numerals but old style dates with Chinese characters, never Arabic numerals.

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 while Arabic numerals are considered very casual and strongly discouraged as in Mainland China.

See also[]

  • Fiscal year

Further reading[]


  1. "House of Commons Journal Volume 8, June 9 1660 (Regicides)". British History Online. Retrieved 2007-03-18. 
  2. At the time, Poland was part of the Russian Empire
  3. "Russia: The October (November) Revolution". Encyclopædia Britannica Online. 2007. Retrieved 2007-03-18. 
  4. Template:Cite paper
  5. BAD LINK! "Regnal Year Conversion Chart". Retrieved 2007-03-19. 
  6. "The Japanese Calendar History". National Diet Library, Japan. 2002. Retrieved 2007-03-19. 
  7. Andrei Lankov (6 Feb 2005). "The Dawn of Modern Korea (266) Lunar Calendar". The Korea Times. Retrieved 2007-03-19.