Old Style and New Style dates

Old Style (or OS) and New Style (or NS) is used in English language historical studies either to indicate that the start of the has been adjusted to start on  (NS) even though contemporary documents use a different start of year (OS); or to indicate that a date conforms to the  (OS), formerly in use in many countries, rather than the  (NS). In and the British colonies the  change of start of the year and the change over from the Julian calendar occurred in 1752 and was enabled by the.

Many other cultures have also changed their calendar system to adopt dating and thus have old and new styles of dating: these are discussed briefly.

Differences between the start of the year
When recording British history it is usual to use the dates recorded at the time of the event with the year adjusted to the start on the. So for example the is universally known to have been fought on,. But the start of the was not always  and was altered at different times in different countries.

From the 12th century to 1752 the year in England began on, so for example the execution of Charles I was recorded at the time in Parliament as happening on  1648 (Old Style). In modern English language texts this date is usually recorded as " 1649" (New Style). A full conversion of the date into the Gregorian calendar is, the date by which his contemporaries in some parts of continental Europe would have recorded his execution.

The OS/NS designation is particularly relevant for dates which fall between the start of the modern year and the start of the contemporary  year, which was  in England  up and until  (see  article).

During the transition years between the first introduction of the Gregorian calendar on continental Europe and its introduction in Britain, contemporary usage in England started to change. In Britain was celebrated as the New Year festival, but the "year starting 25th March was called the Civil or Legal Year, although the phrase Old Style was more commonly used." To reduce misunderstandings on the date, it was not uncommon in parish registers for a new year heading after for example 1661 had another heading at the end of the following December indicating "1661/62". This was to explain to the reader that the year was 1661 Old Style and 1662 New Style.

Differences between Julian and Gregorian dates
The was formerly in use in many European countries and their colonies, rather than the, currently in use in most countries. Consequently and to avoid ambiguity, "Old Style" (OS) and "New Style" (NS) are sometimes added to historical dates to identify which system is being used (when giving a date in the period when both systems were in parallel use). This notation is used in Western European (and colonial) history: similar notations are in use for the equivalent conversions in Eastern Europe and Asia.

For a period of 170 years (1582 – 1752), both dating systems were in concurrent use in different parts of Western Europe and its colonies. The Julian calendar had drifted by 11 days from the solar calendar (due to its surfeit of leap years), so the day and month differ between the systems as well as does the year. System conversion occurred in countries as late as the twentieth century.

countries such as, , , and were first to change to the Gregorian calendar. Thursday,  was followed by Friday, , with ten days "missing". Countries that did not change until the 1700s observed an additional, necessitating eleven "missing days". Some countries did not change until the 1800s or 1900s, necessitating one or two more "missing days".

changed from Julian to Gregorian Calendar on  JU where the next day was   GR. France used the from   GR to   GR.

In, the terms "Old Style" and "New Style" have the same significance as elsewhere. The start of the year was moved to in 1700, but the Gregorian calendar was introduced there much later, in the &mdash;on   (Gregorian calendar). Hence the of 1917 is so called, despite having started on  under the Gregorian calendar ( [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  uses the format of "25 October (7 November, New Style);" to describe the date of the start of the revolution.

It is sometimes remarked that and  died on the same date, , but not on the same day. was still using the Julian calendar in 1616, while was using the Gregorian calendar. Cervantes actually died ten days before Shakespeare.

Possible date conflicts
Occasionally using different calendars has caused confusion between contemporaries. For example one of the contributory factors for 's victory at the 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.

Usually, 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. For example the is universally known to have been fought on , which is. But for the period between the first introduction of the Gregorian calendar on  and its introduction in Britain on , 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 is always given as. However confusion occurs when an event affects both. For example arrived at  in England on  (Julian calendar), after setting sail from the  on  (Gregorian calendar).

The took place only a few months later in Ireland on   "Old Style". However, it is commemorated as taking place on "New Style" by the  parades on "", in spite of  Orangemen's antipathy to Papal innovations. This is in part a conflation of commemorations of the, (OS).

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, 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." , for example, lived during the time Great Britain, Ireland and the British colonies eventually converted to the Gregorian calendar, so he instructed that his tombstone bear his dates of birth and death in the Old Style and New Style, respectively. At Jefferson's birth the difference would have been eleven days between styles, had the New Style been converted to yet, as is evidenced by his "original" birthday of and his New Style birthday of.

Countries that used lunisolar calendars
,, and started using the Gregorian calendar on  of , , and , respectively. They had used 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 may be used for both calendar dates in modern Japanese and Korean languages, but not Chinese.

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

Japan currently employs two calendar systems: Gregorian and modified traditional. 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 is corresponds to  19. An era does not necessarily begin on January 1st.

Korea
Korea started using the Gregorian calendar on, 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 is now used in very limited unofficial purposes only.

China
The started using the Gregorian calendar on , but the lunisolar  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. China,, , and  all have legal holidays based on the lunisolar Chinese calendar, with the most important one being the.

To visually distinguish old and new style dates, /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 s, 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.