Old Style and New Style dates

Memorial plaque to John Etty in All Saints' Church, North Street, York, recording his date of death as 28 January 170+8/9

When recording British history, it is usual to use the same dates recorded at the time of the event, with the year adjusted to start on 1 January.[5] The latter adjustment may be needed because the start of the civil calendar year was not always 1 January and was altered at different times in different countries.[lower-alpha 1] From 1155 to 1752, the civil or legal year in England began on 25 March (Lady Day);[6][7] so for example, the execution of Charles I was recorded at the time in Parliament as happening on 30 January 1648 (Old Style).[8] In newer English language texts this date is usually shown as "30 January 1649" (New Style).[2] The corresponding date in the Gregorian calendar is 9 February 1649, the date by which his contemporaries in some parts of continental Europe would have recorded his execution.

The O.S./N.S. designation is particularly relevant for dates which fall between the start of the "historical year" (1 January) and the official start date, where different. This was 25 March in England, Wales and the colonies until 1752 and until 1600 in Scotland.

During the years between the first introduction of the Gregorian calendar in continental Europe and its introduction in Britain, contemporary usage in England started to change.[4] In Britain, 1 January was celebrated as the New Year festival,[9] but the "year starting 25th March was called the Civil or Legal Year, although the phrase Old Style was more commonly used."[4] To reduce misunderstandings about the date, it was normal in parish registers to place a new year heading after 24 March (for example "1661") and another heading from the end of the following December, 1661/62, a form of dual dating to indicate that in the following twelve weeks or so, the year was 1661 Old Style but 1662 New Style.[10] Some more modern sources, often more academic ones (e.g. the History of Parliament) also use the 1661/62 style for the period between 1 January and 24 March for years before the introduction of the New Style calendar in England.[11]

Scotland had already partly made the change: its calendar year had begun on 1 January since 1600.[12][13]

William Hogarth painting: Humours of an Election (c. 1755), which is the main source for "Give us our Eleven Days".

Through the enactment of the British Calendar (New Style) Act 1750 and of the Irish Parliament's Calendar (New Style) Act, 1750,[14] Great Britain, Ireland and the British Empire (including much of what is now the eastern part of the United States and Canada) 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. Claims that rioters demanded "Give us our eleven days" grew out of a misinterpretation of a painting by William Hogarth.[15] The British tax year traditionally ended on Lady Day (25 March) on the Julian calendar and this became 5 April, which was the "New Style" equivalent.[16] Since then, the British fiscal year has uniquely run from 6 April to 5 April, rather than being coordinated with the calendar year or starting at the beginning of a month as in other countries. Dr Robert Poole explains:[17] "The twelve- rather than eleven-day discrepancy between the start of the old year (25 March) and that of the modern financial year (6 April) has caused puzzlement, [...] In fact, 25 March was first day of the [calendar] year but the last day of the financial quarter, corresponding to 5 April; the difference was thus exactly eleven days".[lower-alpha 2]

It is common in English-language publications to use the familiar Old Style and/or New Style terms to discuss events and personalities in other countries, especially with reference to the Russian Empire and the very beginning of Soviet Russia. 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.[20]

When that usage is encountered, the British adoption date is not necessarily intended. The 'start of year' change and the calendar system change were not always adopted concurrently. Similarly, civil and religious adoption may not have happened at the same time or even at all. In the case of Eastern Europe, for example, all of those assumptions would be incorrect.

Thomas Jefferson's tombstone. Written below the epitaph is "Born April 2 1743 O.S. Died July 4 1826"

Usually, the mapping of New Style dates onto Old Style dates with a start of year adjustment works well with little confusion for events before the introduction of the Gregorian calendar. For example, the Battle of Agincourt is well known to have been fought on 25 October 1415, which is Saint Crispin's Day. However, for the period between the first introduction of the Gregorian calendar on 15 October 1582 and its introduction in Britain on 14 September 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 by using the Gregorian calendar. For example, the Battle of Blenheim is always given as 13 August 1704. However, confusion occurs when an event involves both. For example, William III of England arrived at Brixham in England on 5 November (Julian calendar), after he had set sail from the Netherlands on 11 November (Gregorian calendar) 1688.[21]

The Battle of the Boyne in Ireland took place a few months later on 1 July 1690 (Julian calendar). That maps to 11 July (Gregorian calendar), conveniently close to the Julian date of the subsequent (and more decisive) Battle of Aughrim on 12 July 1691 (Julian). The latter battle was commemorated annually throughout the 18th century on 12 July,[22] following the usual historical convention of commemorating events of that period within Great Britain and Ireland by mapping the Julian date directly onto the modern Gregorian calendar date (as happens, for example, with Guy Fawkes Night on 5 November). The Battle of the Boyne was commemorated with smaller parades on 1 July. However, both events were combined in the late 18th century,[22] and continue to be celebrated as "The Twelfth".

Because of the differences, British writers and their correspondents often employed two dates, which is called dual dating, more or less automatically. Letters concerning diplomacy and international trade thus sometimes bore both Julian and Gregorian dates to prevent confusion. For example, Sir William Boswell wrote to Sir John Coke from The Hague a letter dated "12/22 Dec. 1635".[21] In his biography of John Dee, The Queen's Conjurer, Benjamin Woolley surmises that because Dee fought unsuccessfully for England to embrace the 1583/84 date set for the change, "England remained outside the Gregorian system for a further 170 years, communications during that period customarily carrying two dates".[23] In contrast, Thomas Jefferson, who lived while the British Isles and colonies eventually converted to the Gregorian calendar, instructed that his tombstone bear his date of birth by using the Julian calendar (notated O.S. for Old Style) and his date of death by using the Gregorian calendar.[24] At Jefferson's birth, the difference was eleven days between the Julian and Gregorian calendars and so his birthday of 2 April in the Julian calendar is 13 April in the Gregorian calendar. Similarly, George Washington is now officially reported as having been born on 22 February 1732, rather than on 11 February 1731/32 (Julian calendar).[25]

There is some evidence that the calendar change was not easily accepted. Many British people continued to celebrate their holidays "Old Style" well into the 19th century,[lower-alpha 3] a practice that the author Karen Bellenir considered to reveal a deep emotional resistance to calendar reform.[26]

The change arose from the realisation that the correct figure for the number of days in a year is not 365.25 (365 days 6 hours) as assumed by the Julian calendar but slightly less (c. 365.242 days): the Julian calendar has too many leap years. The consequence was that the basis for calculation of the date of Easter as decided in the 4th century had drifted from reality. The Gregorian calendar reform also dealt with the accumulated difference between these figures, between the years 325 and 1582 (1752 in the British Empire), by skipping 10 days (11 in the case of Great Britain, including its colonies and Ireland) to restore the date of the vernal equinox to approximately 21 March, the approximate date it occurred at the time of the First Council of Nicea in 325.

For a ready reckoner to assist in converting O.S. dates to N.S. and vice versa, see this table.

• Dual dating

Wikisource has original text related to this article: British Calendar Act of 1751

• Details of conversion for many countries
• Side-by-side Old style–New style reference
• Time to Take Note: The 1752 Calendar Change
• Calendar Converter – Date converter for many systems, from John Walker
• Calendar converter to ancient Attic, Armenian, Coptic, and Ethiopian by Academy of Episteme