This articleis missing information about the historical development of calendar dates. Please expand the article to include this information. Further details may exist on thetalk page.(March 2018)
Acalendar date is a reference to a particularday, represented within acalendar system, enabling a specific day to be unambiguously identified. Simple math can be performed between dates; commonly, the number of days between two dates may be calculated, e.g., "25 February 2026" is ten days after "15 February 2026". The date of a particular event depends on thetime zone used to record it. For example, theair attack on Pearl Harbor that began at 7:48 a.m. localHawaiian time (HST) on 7 December 1941 is recorded equally as having happened on 8 December at 3:18 a.m.Japan Standard Time (JST).
In most calendar systems, the date consists of three parts: the (numbered)day of the month, themonth, and the (numbered)year. There may also be additional parts, such as theday of the week. Years are counted from a particular starting point called theepoch, withera referring to the span of time since that epoch.[b] A date without the year may also be referred to as adate orcalendar date (such as "13 February" rather than "13 February 2026"). As such, it is either shorthand for the current year, or else it defines the day of an annual event such as a birthday on 25 March or Christmas on 25 December.
"Date mask" redirects here. For non-medical mask-wearing in Japan, seeDate face mask.
Day-Month-Year
Year-Month-Day
Month-Day-Year
DMY and YMD
DMY and MDY
MDY and YMD
MDY, DMY, and YMD
A large variety of formats for dates is in use in line with differing national or other convention, that differ according to the order of date element and separators. For example the date "25 March 1995" can be written as25/03/1995 (DMY convention),03/25/1995 (MDY convention),1995/03/25 (YMD convention}; using different types of separator (e.g.,25.03.1995,25/03/1995,25-03-1995,25 03 1995), whether leading zeros are included (e.g.25/3/1995 vs.25/03/1995), whether all four digits of the year are written (e.g.,25.03.1995 vs.25.03.95), and whether the month is represented inArabic orRoman numerals or by name (e.g. 25.03.1995, 25.III.1995, 25 March 1995). The format chosen for display of the date can be location or user dependent and is sometimes called adate mask in database administration.[citation needed] Actual presentation in a given context is controlled byinput masks and output masks. (The name comes from the metaphor that, just as the same person can look different superficially by putting on any of various masks in amasquerade, the underlying value representing a date can have different presentations.)
Thislittle-endian sequence is used by a majority of the world and is the preferred form by theUnited Nations when writing the full date format in official documents. This date format originates from the custom of writing the date as "the Nth day of [month] in the year of our Lord [year]" in Western religious and legal documents. The format has shortened over time but the order of the elements has remained constant. The following examples use the date of 25 March 1995. In the case of two-digit years, care must be taken to ensure thatthey are not interpreted as belonging to a different century (e.g. "01" being interpreted as "1901" instead of "2001"). The dots function asordinal dots.
25 March 1995
25/3/1995 or 25/03/1995
25.3.1995 or 25.03.1995
25. 3. 1995 or 25. 03. 1995
25-3-1995 or 25-03-1995
25-Mar-1995
25Mar95 – Used, including in the U.S., where space needs to be saved by skippingpunctuation (often seen on thedateline of Internet news articles).
[The] 25th [of] March 1995 – 'The' and 'of' are often spoken but generally omitted in all but the most formal writing such as legal documents.
25/iii/95, 25.iii.95, 25-iii.95, 25/iii-95, 25.III.1995, 25. III. 1995 or 25 III 1995 (using theRoman numeral for the month) – In the past, this was a common and typical way of distinguishing day from month and was widely used in many countries, but recently this practice has been affected by the general retreat from the use of Roman numerals.[citation needed] This is usually confined to handwriting only and is not put into any form of print.[citation needed] It is associated with a number of schools and universities. It has also been used by the Vatican as an alternative to using months named after Roman deities.[citation needed] It is used on Canadian postmarks as abilingual form of the month. It was also commonly used in theSoviet Union, in both handwriting and print.
In this format, the most significant data item is written before lesser data items i.e. the year before the month before the day. It is consistent with thebig-endianness of theHindu–Arabic numeral system, which progresses from the highest to the lowest order magnitude. That is, using this format textual orderings and chronological orderings are identical. This form is standard in East Asia, Iran, Lithuania, Hungary, and Sweden; and some other countries to a limited extent.
Examples for the 25th of March 1995:
1995-03-25: the standard Internet date/time format,[2] a profile of the international standardISO 8601, orders the components of a date like this, and additionally uses leading zeros, for example, 1995-03-25, to be easily read and sorted by computers. It is used withUTC in RFC 3339. This format is also favored in certainAsian countries, mainlyEast Asian countries, as well as in some European countries. The big-endian convention is also frequently used inCanada, but all three conventions are used there (both endians and the American MMDDYYYY format are allowed on Canadian bank cheques provided that the layout of the cheque makes it clear which style is to be used).[3]
1995 March 25
1995Mar25
1995-Mar-25
1995-Mar-25, Saturday
1995. march 25. – The official format inHungary, point after year and day, month name with small initial. Following shorter formats also can be used: 1995. mar. 25., 1995. 03. 25., 1995. III. 25.
1995.3.25 or 1995.03.25
1995/3/25 or 1995/03/25
1995/3/25 or 1995/03/25
95/3/25 or 95/03/25
19950325 : the "basic format" profile of ISO 8601, an 8-digit number providingmonotonic date codes, common in computing and increasingly used in dated computer file names. It is used in the standardiCalendar file format defined in RFC 5545.
It is also extended through the universal big-endian format clock time: 1995 March 25, 18h 14m 12s, or 1995/03/25/18:14:12 or (ISO 8601) 1995-03-25T18:14:12.
This sequence is used primarily in thePhilippines and theUnited States. It is also used to varying extents inCanada (though never inQuebec).[4] This date format was commonly used alongside the little-endian form in the United Kingdom until the mid-20th century and can be found in both defunct and modern print media, such as theLondon Gazette andThe Times, respectively. This format was also commonly used by several English-language print media in many former British colonies and also one of two formats commonly used in India duringBritish Raj era until the mid-20th century.
Saturday, March 25, 1995
March 25, 1995
Mar 25, 1995
Mar-25-1995
Mar-25-1995
3/25/1995 or 03/25/1995
3-25-1995 or 03-25-1995
3.25.1995 or 03.25.1995
3.25.95 or 03.25.95
3/25/95 or 03/25/95
Modern style guides recommend avoiding the use of the ordinal (e.g. 1st, 2nd, 3rd, 4th) form of numbers when the day follows the month (July 4),[5][6] and that format is not included inISO standards.[7] The ordinal was common in the past and is still sometimes used ([the] 4th [of] July orJuly 4th).
This date format is used inKazakhstan,Latvia,Nepal, andTurkmenistan. According to the official rules of documenting dates by governmental authorities,[8] the long date format in Kazakh is written in the year–day–month order, e.g. 1995 25 March (Kazakh:1995 жылғы 25 наурыз). However, both Latvia and Kazakhstan use the day-month-year format (DD.MM.YYYY or DD/MM/YYYY) for all-numeric dates.[9][10] None of these four countries use the all-numeric date format YYYY.DD.MM
There are several standards that specify date formats:
ISO 8601Data elements and interchange formats – Information interchange – Representation of dates and times specifiesYYYY-MM-DD (the separators are optional, but only hyphens are allowed to be used), where all values are fixed length numeric, but also allowsYYYY-DDD, whereDDD is the ordinal number of the day within the year, e.g. 2001–365.[11]
RFC 3339Date and Time on the Internet: Timestamps specifiesYYYY-MM-DD, i.e. a particular subset of the options allowed by ISO 8601.[12]
RFC 5322Internet Message Format specifiesday month year whereday is one or two digits,month is a three letter month abbreviation, andyear is four digits.[13]
Many numerical forms can create confusion when used in international correspondence, particularly when abbreviating the year to its final two digits, with no context. For example, "07/08/06" could refer to either 7 August 2006 or July 8, 2006 (or 1906, or the sixth year of any century), or 2007 August 6.
The date format of YYYY-MM-DD in ISO 8601, as well as other international standards, have been adopted for many applications for reasons including reducing transnational ambiguity and simplifying machine processing.[14]
When transitioning from one calendar or date notation to another, a format that includes both styles may be developed; for exampleOld Style and New Style dates in the transition from the Julian to the Gregorian calendar.[16]
One of the advantages of using theISO 8601 date format is that thelexicographical order (ASCIIbetical) of the representations is equivalent to the chronological order of the dates, assuming that all dates are in the same time zone. Thus dates can be sorted using simple string comparison algorithms, and indeed by any left to rightcollation. For example:
2003-02-28 (28 February 2003) sorts before2006-03-01 (1 March 2006) which sorts before2015-01-30 (30 January 2015)
The YYYY-MM-DD layout is the only common format that can provide this.[17] Sorting other date representations involves someparsing of the date strings. This also works when a time in 24-hour format is included after the date, as long as all times are understood to be in the same time zone.
ISO 8601 is used widely where concise, human-readable yet easily computable and unambiguous dates are required, although many applications store dates internally asUNIX time and only convert to ISO 8601 for display. All modern computerOperating Systems retain date information of files outside of their titles, allowing the user to choose which format they prefer and have them sorted thus, irrespective of the files' names.
The U.S. military sometimes uses a system, known to them as the "Julian date format",[18] which indicates the year and the actual day out of the 365 days of the year (and thus a designation of the month would not be needed). For example, "11 December 1999" can be written in some contexts as "1999345" or "99345", for the 345th day of 1999.[19] This system is most often used in US military logistics since it simplifies the process of calculating estimated shipping and arrival dates. For example: say a tank engine takes an estimated 35 days to ship by sea from the US to South Korea. If the engine is sent on 06104 (Friday, 14 April 2006), it should arrive on 06139 (Friday, 19 May). Outside of the US military and some US government agencies, including theInternal Revenue Service, this format is usually referred to as "ordinal date", rather than "Julian date".[20]
Such ordinal date formats are also used by many computer programs (especially those for mainframe systems). Using a three-digitJulian day number saves one byte of computer storage over a two-digit month plus two-digit day, for example, "January 17" is 017 in Julian versus 0117 in month-day format.OS/390 or its successor,z/OS, display dates in yy.ddd format for most operations.
UNIX time stores time as a number in seconds since the beginning of the UNIX Epoch (1970-01-01).
Another "ordinal" date system ("ordinal" in the sense of advancing in value by one as the date advances by one day) is in common use in astronomical calculations and referencing and uses the same name as this "logistics" system. The continuity of representation of period regardless of the time of year being considered is highly useful to both groups of specialists. The astronomers describe their system as also being a "Julian date" system.[21]
Companies in Europe often use year, week number, and day for planning purposes. So, for example, an event in a project can happen onw43 (week 43) orw43-1 (Monday, week 43) or, if the year needs to be indicated, onw0643 (the year 2006, week 43; i.e., Monday 23October–Sunday 29October 2006).
AnISO week-numbering year has 52 or 53 full weeks. That is 364 or 371 days instead of the conventional Gregorian year of 365 or 366 days. These 53 week years occur on all years that have Thursday as 1 January and on leap years that start on Wednesday the 1 January. The extra week is sometimes referred to as a 'leap week', although ISO 8601 does not use this term.
InEnglish-language outside North America (mostly in Anglophone Europe and some countries in Australasia), full dates are written as7 December 1941 (or7th December 1941) and spoken as "the seventh of December, nineteen forty-one" (exceedingly common usage of "the" and "of"), with the occasional usage ofDecember 7, 1941 ("December the seventh, nineteen forty-one"). In common with most continental European usage, however, all-numeric dates are invariably ordered dd/mm/yyyy.
InCanada and theUnited States, the usual written form isDecember 7, 1941, spoken as "December seventh, nineteen forty-one" or colloquially "December the seventh, nineteen forty-one".Ordinal numerals, however, are not always used when writing and pronouncing dates, and "December seven, nineteen forty-one" is also an accepted pronunciation of the date writtenDecember 7, 1941. A notable exception to this rule is theFourth of July (U.S.Independence Day).
^An identifying suffix may be needed where ambiguity may arise, but this may not always be sufficient. For example, the Western (Gregorian) and Eastern (Julian) Christian calendars each use the designation AD but, sinceabout the middle of the 16th century, the same day is dated differently by the calendars, despite each using the same format. Consequently the name of the calendar must also be stated. See alsoOld Style and New Style dates for the notation used followind a change of civil calendar used.
^For details of the [typically retrospective] calculation of the epoch for each calendar, see their respective articles.
^Dershowitz, D.;Reingold, E. M (2008).Calendrical Calculations (3rd ed.). Cambridge: Cambridge University Press. p. 45.The calendar in use today in most of the world is the Gregorian ornew-style calendar designed by a commission assembled by Pope Gregory XIII in the sixteenth century.
^Spathaky, Mike."Old Style and New Style Dates and the change to the Gregorian Calendar". Retrieved19 August 2023.. "Before 1752, parish registers, in addition to a new year heading after 24th March showing, for example '1733', had another heading at the end of the following December indicating '1733/4'. This showed where the Historical Year 1734 started even though the Civil Year 1733 continued until 24th March. ... We as historians have no excuse for creating ambiguity and must keep to the notation described above in one of its forms. It is no good writing simply 20th January 1745, for a reader is left wondering whether we have used the Civil or the Historical Year. 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."
^E. Kelly Taylor,America's Army and the Language of Grunts: Understanding the Army Lingo Legacy (Bloomington IN: AuthorHouse, 2009), 185.ISBN1438962509, 9781438962504
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