This is a tracking category for CS1 citations with date-holding parameters where the date values do not comply with MOS:DATEFORMAT.

Help desk

When Citation Style 1 and Citation Style 2 templates contain date-holding parameters, an automated test is done to see if the dates are real dates that comply with a subset of the date rules in Wikipedia's Manual of Style, specifically checking for violations of MOS:DATEFORMAT.

To resolve this error, ensure that the date is an actual date and that the date format follows the Wikipedia Manual of Style's guidance on dates in the named parameter. See examples of unacceptable dates and how to fix them, below. Or, some conceptual issues to look for:

• impossible dates, such as 29 February 2011 (2011 was not a leap year)
• |access-date= must specify a day, not just a month or year.
• misplaced, incorrect, or extraneous punctuation
• extraneous text
• hyphens or slashes instead of en dashes in date ranges (en dashes are required)
• misspelling or improper capitalization (see MOS:ALLCAPS for more detail that is not in Wikipedia Manual of Style's guidance on dates)
• other unacceptable date formats listed in MOS:BADDATEFORMAT
• more than one date in a date-holding parameter
• years before 100 AD, including BCE/BC dates. Try using parameter |orig-date= instead.

See Help: Citation Style 1 for information about limitations in the CS1 citation templates' handling of date formats. The MOS section on date ranges describes how to separate dates in a date range. Do not use  , –, or {{spaced ndash}} as these corrupt the metadata. To add an en dash, use the CharInsert edit tool or see Wikipedia:How to make dashes. You may also use this one: –. A bot is often able to correct the separator, provided the overall format is unambiguous.

Future dates in |date= in CS1|2 citations are limited to current year + 1; that is, for 2021, citation dates in 2022 are acceptable but citation dates in 2023 and beyond are not.

Dates prior to 1582 are treated as Julian calendar dates. Dates from 1582 onward are treated as Gregorian calendar dates. The Julian calendar was used in some places until approximately 1923. Three Julian calendar dates in the overlap period, 29 February in the years 1700, 1800, and 1900, will cause this error message because those years are not leap years in the Gregorian calendar.

The access date (in |access-date=) is checked to ensure that it contains a full date (day, month, and year) and is between 15 January 2001 (the founding date of Wikipedia) and today's date plus one day, because it represents the date that an editor viewed a web-based source to verify a statement on Wikipedia. Because editors may be in time zones that are one day ahead of the UTC date, one extra day is accepted.

Pages with this error are automatically placed in Category:CS1 errors: dates (10,250 pages).^[a]

By default, Citation Style 1 and Citation Style 2 error messages are visible to all readers and maintenance category messages are hidden from all readers.

To display maintenance messages, include the following text in your common CSS page or your specific skin's CSS page (common.css and skin.css respectively):

.mw-parser-output span.cs1-maint {display: inline;} /* display Citation Style 1 maintenance messages */

To display hidden-by-default error messages:

.mw-parser-output span.cs1-hidden-error {display: inline;} /* display hidden Citation Style 1 error messages */

Even with this CSS installed, older pages in Wikipedia's cache may not have been updated to show these error messages even though the page is listed in one of the tracking categories. A null edit will resolve that issue.

To hide normally-displayed error messages:

.mw-parser-output span.cs1-visible-error {display: none;} /* hide Citation Style 1 error messages */

You can personalize the display of these messages (such as changing the color), but you will need to ask someone who knows CSS or at the technical village pump if you do not understand how.

Notes