Editing Calendar date (section)

==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",<ref>{{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}}</ref> 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.<ref name="km-iso">{{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}}</ref> 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".<ref>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.</ref>

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

===Week number used===
{{more|ISO week date|Leap week calendar}}
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 date|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|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 number (linguistics)|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 (United States)|Independence Day]]).