Calendar date#Gregorian, day–month–year (DMY)

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A calendar date is a reference to a particular day, represented within a calendar 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 {{CURRENTMONTHNAME}} {{CURRENTYEAR}}" is ten days after "15 {{CURRENTMONTHNAME}} {{CURRENTYEAR}}". The date of a particular event depends on the time zone used to record it. For example, the air attack on Pearl Harbor that began at 7:48 a.m. local Hawaiian time (HST) on 7 December 1941 is recorded equally as having happened on 8 December at 3:18 a.m. Japan Standard Time (JST).

A particular day may be assigned a different nominal date according to the calendar used.{{efn|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, since about 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 also Old Style and New Style dates for the notation used followind a change of civil calendar used.}} The de facto standard for recording dates worldwide is the Gregorian calendar, the world's most widely used civil calendar.{{cite book|author-link1=Nachum Dershowitz |last1= Dershowitz | first1= D. |author-link2=Edward Reingold | last2=Reingold |first2= E. M |year= 2008 | title= Calendrical Calculations | edition = 3rd |publisher= Cambridge University Press | location = Cambridge | page= 45 | quote=The calendar in use today in most of the world is the Gregorian or new-style calendar designed by a commission assembled by Pope Gregory XIII in the sixteenth century.}} Many cultures use religious calendars such as the Gregorian (Western Christendom, AD), the Julian calendar (Eastern Christendom, AD), Hebrew calendar (Judaism, AM), the Hijri calendars (Islam, AH), or any other of the many calendars used around the world. Regnal calendars (that record a date in terms of years since the beginning of the monarch's reign) are also used in some places, for particular purposes.

In most calendar systems, the date consists of three parts: the (numbered) day of the month, the month, and the (numbered) year. There may also be additional parts, such as the day of the week. Years are counted from a particular starting point called the epoch, with era referring to the span of time since that epoch.{{efn|For details of the [typically retrospective] calculation of the epoch for each calendar, see their respective articles.}} A date without the year may also be referred to as a date or calendar date (such as "{{CURRENTDAY}} {{CURRENTMONTHNAME}}" rather than "{{CURRENTDAY}} {{CURRENTMONTHNAME}} {{CURRENTYEAR}}"). 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 31 May or Christmas on 25 December.

Date format

File:Date format by country 3.svg

There is a large variety of formats for dates in use, which differ in the order of date components. These variations use the sample date of 31 May 2006: (e.g. 31/05/2006, 05/31/2006, 2006/05/31), component separators (e.g. 31.05.2006, 31/05/2006, 31-05-2006), whether leading zeros are included (e.g. 31/5/2006 vs. 31/05/2006), whether all four digits of the year are written (e.g., 31.05.2006 vs. 31.05.06), and whether the month is represented in Arabic or Roman numerals or by name (e.g. 31.05.2006, 31.V.2006 vs. 31 May 2006).

=Gregorian, day–month–year (DMY) =

File:Příležitostné razítko pof. PR7, 13.06.1939.jpg

This little-endian sequence is used by a majority of the world and is the preferred form by the United 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 9 November 2006. (With the years 2000–2009, care must be taken to ensure that two digit years do not intend to be 1900–1909 or other similar years.) The dots have a function of ordinal dot.

"9 November 2006" or "9. November 2006" (the latter is common in German-speaking regions)
9/11/2006 or 09/11/2006
09.11.2006 or 9.11.2006
9. 11. 2006
9-11-2006 or 09-11-2006
09-Nov-2006
09Nov06 – Used, including in the U.S., where space needs to be saved by skipping punctuation (often seen on the dateline of Internet news articles).
[The] 9th [of] November 2006 – 'The' and 'of' are often spoken but generally omitted in all but the most formal writing such as legal documents.
09/Nov/2006 – used in the Common Log Format
Thursday, 9 November 2006
9/xi/06, 9.xi.06, 9-xi.06, 9/xi-06, 9.XI.2006, 9. XI. 2006 or 9 XI 2006 (using the Roman 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.{{cn|date=August 2021}} This is usually confined to handwriting only and is not put into any form of print.{{Citation needed|date=August 2021}} 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.{{cn|date=August 2021}} It is used on Canadian postmarks as a bilingual form of the month. It was also commonly used in the Soviet Union, in both handwriting and print.
9 November 2006 CE or 9 November 2006 AD

=Gregorian, year–month–day (YMD) =

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 the big-endianness of the Hindu–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 9th of November 2003:

2003-11-09: the standard Internet date/time format,[http://www.w3.org/TR/NOTE-datetime W3C Date and Time Formats] Internet date/time format a profile of the international standard ISO 8601, orders the components of a date like this, and additionally uses leading zeros, for example, 1996-05-01, to be easily read and sorted by computers. It is used with UTC in RFC 3339. This format is also favored in certain Asian countries, mainly East Asian countries, as well as in some European countries. The big-endian convention is also frequently used in Canada, 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).{{cite web|url=http://www.cdnpay.ca/news/new_cheque_specs.asp |title=Canadian Payments Association – Specifications for Imageable Cheques and Other Payment Items |url-status=dead |archive-date=6 July 2010 |archive-url=https://web.archive.org/web/20100706223651/http://www.cdnpay.ca/faqs/new_specifications.asp |date=February 3, 2009 |quote=Adoption of a numeric date field in one of three specified formats (YYYYMMDD, MMDDYYYY or DDMMYYYY. It is essential that field indicators be printed below the date field to indicate which format is being used.}}
2003 November 9
2003Nov9 or 2003Nov09
2003-Nov-9 or 2003-Nov-09
2003-Nov-9, Sunday
2003. {{sic|hide=y|no|vember}} 9. – The official format in Hungary, point after year and day, month name with small initial. Following shorter formats also can be used: 2003. {{sic|hide=y|nov}}. 9., 2003. 11. 9., 2003. XI. 9.
2003.11.9 using dots and no leading zeros, common in China.
2003.11.09
2003/11/09 using slashes and leading zeros, common in Japan on the Internet.
2003/11/9
03/11/09
20031109 : the "basic format" profile of ISO 8601, an 8-digit number providing monotonic date codes, common in computing and increasingly used in dated computer file names. It is used in the standard iCalendar file format defined in RFC 5545. A big advantage of the ISO 8601 "basic format" is that a simple textual sort is equivalent to a sort by date.

It is also extended through the universal big-endian format clock time: 2003 November 9, 18h 14m 12s, or 2003/11/9/18:14:12 or (ISO 8601) 2003-11-09T18:14:12.

=Gregorian, month–day–year (MDY)=

{{See also|Date and time notation in the United States|Date and time notation in Canada}}

This sequence is used primarily in the Philippines and the United States. It is also used to varying extents in Canada (though never in Quebec).{{cite news |last=Sanderson |first=Blair |title=Proposed legislation aims to settle date debate |url=https://www.cbc.ca/news/canada/proposed-legislation-aims-to-settle-date-debate-1.3407640 |access-date=25 September 2017 |work=CBC News |date=18 January 2016}} 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 the London Gazette and The 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 during British Raj era until the mid-20th century.

Thursday, November 9, 2006
November 9, 2006
Nov 9, 2006
Nov-9-2006
Nov-09-2006
11/9/2006 or 11/09/2006
11-09-2006 or 11-9-2006
11.09.2006 or 11.9.2006
11.09.06
11/09/06

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 or July 4, 2024),{{cite report |author=Washington Journalism Education Association |date=February 21, 2014 |title=Associated Press Style 'Cheat Sheet' |url=https://wjea.org/wp-content/uploads/2014/02/WJEA-AP-Style-Cheat-Sheet.pdf |publisher=Washington Journalism Education Association |access-date=2024-06-15}}{{cite web | title=Australian Government Style Manual: Dates and time | website=Australian Government | date=2020-12-31 | url=https://www.stylemanual.gov.au/grammar-punctuation-and-conventions/numbers-and-measurements/dates-and-time#follow_australian_conventions_for_dates | access-date=2024-06-16}} and that format is not included in ISO standards.{{cite web | title=SO/DIS 34000(en) Date and time — Concepts and vocabulary | website=ISO | url=https://www.iso.org/obp/ui/fr/#iso:std:iso:34000:dis:ed-1:v1:en:term:7.8 | access-date=2024-06-16}} The ordinal was common in the past and is still sometimes used ([the] 4th [of] July or July 4th).

=Gregorian, year–day–month (YDM)=

This date format is used in Kazakhstan, Latvia, Nepal, and Turkmenistan. According to the official rules of documenting dates by governmental authorities,{{Cite web| url=http://adilet.zan.kz/kaz/docs/V1400010129 | publisher=Government of Kazakhstan (in Kazakh) | title=Official rules of documenting in governmental authorities}} the long date format in Kazakh is written in the year–day–month order, e.g. 2006 5 April ({{langx|kk|2006 жылғы 05 сәуір}}). However, both Latvia and Kazakhstan use the day-month-year format (DD.MM.YYYY or DD/MM/YYYY) for all-numeric dates.{{Cite web |title=Kā latviešu valodā pareizi rakstāms datums? |url=https://www.diena.lv/raksts/pasaule/krievija/ka-latviesu-valoda-pareizi-rakstams-datums-10007855 |access-date=2025-02-27 |website=www.diena.lv}}{{Cite web |title=Статистическая карта амбулаторного пациента для консультативно-диагностических центров (поликлиник). Форма 025-9/у (утверждена приказом и.о. Министра здравоохранения Республики Казахстан от 8 июля 2005 года № 332) (утратила силу) |url=https://online.zakon.kz/Document/?doc_id=30548668 |access-date=2025-02-27 |website=Информационная система ПАРАГРАФ |language=ru}}

=Standards=

There are several standards that specify date formats:

ISO 8601 Data elements and interchange formats – Information interchange – Representation of dates and times specifies YYYY-MM-DD (the separators are optional, but only hyphens are allowed to be used), where all values are fixed length numeric, but also allows YYYY-DDD, where DDD is the ordinal number of the day within the year, e.g. 2001–365.{{cite web| url = http://www.iso.org/iso/catalogue_detail?csnumber=40874| title = ISO 8601:2004 Data elements and interchange formats – Information interchange – Representation of dates and times}}
RFC 3339 Date and Time on the Internet: Timestamps specifies YYYY-MM-DD, i.e. a particular subset of the options allowed by ISO 8601.{{Cite IETF |rfc=3339 |section=5.6 |title=Date and Time on the Internet: Timestamps |sectionname=5.6 Internet Date/Time Format}}
RFC 5322 Internet Message Format specifies day month year where day is one or two digits, month is a three letter month abbreviation, and year is four digits.{{Cite IETF |rfc=5322 |section=3.3 |title=Internet Message Format |sectionname=3.3 Date and Time Specification}}

=Difficulties=

File:Memorial to John Etty (18373251064).jpg, uses dual dating style to record his date of death as "28 of Jan: {{sfrac|170|8|9}}" ]]

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.{{Cite web |title=International standard date and time notation |url=https://fits.gsfc.nasa.gov/iso-time.html#:~:text=This%20standard%20notation%20helps%20to,traditional%20date%20and%20time%20notations. |access-date=2024-05-01 |website=fits.gsfc.nasa.gov}}

An early U.S. Federal Information Processing Standard recommended 2-digit years. This is now widely recognized as extremely problematic, because of the year 2000 problem. Some U.S. government agencies now use ISO 8601 with 4-digit years.{{cite web |title=Date Format for Web site – Information Systems Department Release |date=2002-07-01 |website=Nye County, Nevada |url=http://www.nyecounty.net/iso8601.html |archive-url=https://web.archive.org/web/20080221020451/http://www.nyecounty.net/iso8601.html|archive-date=February 21, 2008}}{{bsn|reason=It is not clear at what point the piece is copied from elsewhere, so find the original -- possibly by Arthur David Olson at the tz nih archive.|date=November 2023}}

When transitioning from one calendar or date notation to another, a format that includes both styles may be developed; for example Old Style and New Style dates in the transition from the Julian to the Gregorian calendar.{{cite web |last=Spathaky |first=Mike |url=https://www.cree.name/genuki/dates.htm |title=Old Style and New Style Dates and the change to the Gregorian Calendar |access-date=19 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."

Advantages for ordering in sequence

One of the advantages of using the ISO 8601 date format is that the lexicographical 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 right collation. For example:

2003-02-28 (28 February 2003) sorts before

2006-03-01 (1 March 2006) which sorts before

2015-01-30 (30 January 2015)

The YYYY-MM-DD layout is the only common format that can provide this.{{cite web| url=http://www.w3.org/International/questions/qa-date-format | access-date=2008-10-21 | title=FAQ: Date formats | publisher=World Wide Web Consortium (W3C) }} Sorting other date representations involves some parsing 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 as UNIX time and only convert to ISO 8601 for display. All modern computer Operating 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.

Specialized usage

=Day and year only=

{{See also|calendar|time|date-time group|Japanese calendar|Wikibooks:English in Use/Time and Date}}

The U.S. military sometimes uses a system, known to them as the "Julian date format",{{Cite web |last=Hynes |first=John |title=A summary of time formats and standards |url=http://www.decimaltime.hynes.net/p/dates.html |access-date=2011-02-09 |website=www.decimaltime.hynes.net}} 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.{{Cite web |title=International standard date and time notation |url=https://www.cl.cam.ac.uk/~mgk25/iso-time.html |access-date=2024-05-01 |website=www.cl.cam.ac.uk}} 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 the Internal Revenue Service, this format is usually referred to as "ordinal date", rather than "Julian date".Department of Defense. [https://web.archive.org/web/20110322220024/http://www.dtic.mil/whs/directives/corres/pdf/06-MAPAD_DEFINITIONS_TERMS_12-17-01.pdf "Definition of Terms."] March 11, 1997. Retrieved October 24, 2011.

Such ordinal date formats are also used by many computer programs (especially those for mainframe systems). Using a three-digit Julian 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.E. Kelly Taylor, America's Army and the Language of Grunts: Understanding the Army Lingo Legacy (Bloomington IN: AuthorHouse, 2009), 185. {{ISBN|1438962509}}, 9781438962504

=Week number used=

Companies in Europe often use year, week number, and day for planning purposes. So, for example, an event in a project can happen on {{code|w43}} (week 43) or {{code|w43-1}} (Monday, week 43) or, if the year needs to be indicated, on {{code|w0643}} (the year 2006, week 43; i.e., Monday 23{{nbsp}}October{{ndash}}Sunday 29{{nbsp}}October 2006).

An ISO 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.

=Expressing dates in spoken English=

In English-language outside North America (mostly in Anglophone Europe and some countries in Australasia), full dates are written as 7 December 1941 (or 7th December 1941) and spoken as "the seventh of December, nineteen forty-one" (exceedingly common usage of "the" and "of"), with the occasional usage of December 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.

In Canada and the United States, the usual written form is December 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 written December 7, 1941. A notable exception to this rule is the Fourth of July (U.S. Independence Day).

Notes

References

External links

IETF: {{IETF RFC|3339|link=no}}
[http://www.hermetic.ch/cal_stud/formats.htm The ISO 8601 Date Format]
{{cite web|url=http://www-01.ibm.com/software/globalization/locales/index.jsp |title=Globalization locale database |access-date=2008-10-13 |publisher=IBM |url-status=dead |archive-url=https://web.archive.org/web/20090426205632/http://www-01.ibm.com/software/globalization/locales/index.jsp |archive-date=April 26, 2009 }}
{{cite web| url=http://www.microsoft.com/globaldev/nlsweb/default.mspx | title=NLS (National Language Support) information page | publisher=Microsoft | access-date=2008-10-13 | archive-url = https://web.archive.org/web/20080315070046/http://www.microsoft.com/globaldev/nlsweb/default.mspx| archive-date = March 15, 2008}}
{{IETF RFC|2550|link=no}}: Y10K and Beyond
[https://web.archive.org/web/20170629105125/http://www.curiousnotions.com/todays-date.asp Today's date (Gregorian) in over 400 more-or-less obscure foreign languages]

Date