Wikipedia:Manual of Style/Dates and numbers/Date autoformatting

Since at least 2004, it has been possible for registered users to set a preference regarding the way dates appear to them. Wikilinking all dates / years purely for the use of autoformatting is now discouraged (See MOS:UNLINKDATES).

There are four possible formats to choose from:

• MonthName Day, Year as in January 15, 2001 (symbolized as MMMM dD, YYYY)
• Day MonthName Year as in 15 January 2001 (symbolized as dD MMMM YYYY)
• Year MonthName Day as in 2001 January 15 (symbolized as YYYY MMMM DD)
• Year-MonthNumber-Day as in 2001-01-15 (symbolized as YYYY-MM-DD) Though not identified as such on the preferences page, this is the same way dates are displayed in ISO 8601 format.

Dates that are wikilinked (see below) are autoformatted according to the user's chosen preference.

Autoformatting dates has had several disadvantages:

• Its effects can only be seen by registered editors who select a date preference (My preferences → Date and time → Date format). (As with other interface modifications, unregistered users are unable to access Wikipedia's preference settings and cannot choose a date format preference.) Therefore, most of the very individuals who have been largely responsible for the correctness and good style of articles have not seen what the vast majority of readers see.
  • As a result, editors did not notice that the source code often had two (or possibly more) date formats in the same article, while most users saw inconsistent date formats on the same page.
  • Some dates were entered in source code in one or more of the last two formats. While most editors did not notice this, most users saw a format that was much less familiar to them than either MDY or DMY.
• Autoformatting is implemented by wikilinking dates. The resulting links point to articles on notable events that happened on that particular date or year. Since these lists of historical trivia typically have little or nothing to do with the subject of the article linked from, the links are superfluous, and only serve to clutter articles unnecessarily. All links from articles should be of high value to the reader, that is, following them should genuinely help the reader understand the topic more fully. (See WP:CONTEXT.)
• The last format, being most like ISO 8601, was sometimes referred to as being ISO format. However, ISO 8601 format implies use of the Gregorian calendar, and Wikipedia normally uses the Julian calendar for historic dates before the adoption of the Gregorian calendar—all dates before 1582, many before 1752, and some as late as the twentieth century. Autoformatting into and out of this format could be misleading or erroneous for dates on the Julian Calendar, if one thought this format was truly ISO 8601.

The following information is provided to document how date autoformatting works.

A combination of a day and a month, plus optionally a year, is autoformatted by adding square brackets, such as in these examples:

• [[5 November]]
• [[November 5]]
• [[5 November]] [[1989]]
• [[November 5]], [[1989]]

The square brackets instruct the MediaWiki software to format the item according to a user's date preferences.

The following table shows how the autoformatting mechanism behaves. The preference settings that a registered user can choose are displayed in the second row. The year and the day-month combination are wikilinked separately, except for dates in the ISO 8601 format. Full date formats not found in the first column are not autoformatted when wikilinked, and are likely to produce a redlink; for instance,

• [[2005 May 15]] will present "2005 May 15", and
• [[April 17, 1883]] will present "April 17, 1883"

to all users, regardless of their date preference (or non-preference).

• However [[May 15, 2005]], but no other format, will produce a wikilink to a separate page for May 15, 2005. This is true for all dates from January 1, 2003 (retrieved by typing [[January 1, 2003]]) to July 31, 2005.

What you type	What logged-in registered users see (settings on first row)					What others will see [A]
	January 15, 2001	15 January 2001	2001 January 15	2001-01-15	No preference
[[May 15]]	May 15	15 May	May 15	May 15	May 15	May 15
[[15 May]]	May 15	15 May	15 May	15 May	15 May	15 May
[[May 15]], [[2005]]	May 15, 2005	15 May 2005	2005 May 15	2005-05-15	May 15, 2005	May 15, 2005
[[15 May]] [[2005]]	May 15, 2005	15 May 2005	2005 May 15	2005-05-15	15 May 2005	15 May 2005
[[2005-05-15]] [B]	May 15, 2005	15 May 2005	2005 May 15	2005-05-15	2005-05-15	2005-05-15

Even when surrounded by square brackets, those dates that do not contain both a day and a month—such as solitary months, solitary days of the week, solitary years, decades, centuries, and month-year combinations—are not autoformatted. One could make them links by using the standard piped-link notation, but the same advice applies here: such links should not be created unless they are of high value to the reader. (See WP:CONTEXT.)

• Autoformatting does not function for piped links to date elements, such as "[[20 June|the 20th of June]]" or "[[1997 in South African sport|1997]]". (Several forms of piped links override the date-formatting function.)
• Links to date ranges in the same calendar month, such as "[[December 13–17]]" or "the night of [[30/31 May]]" cause autoformatting to fail. The autoformatting mechanism will output such dates in a damaged form: 30/May 31, etc.

Date elements on disambiguation pages and section headings should never be linked; the same applies to quotations, unless the original quote is linked.