A date in a calendar is a reference to a particular day by means of a calendar system. The calendar date allows the particular day to be identified and relative to all other dates. For example February 17, 2003 is ten days after February 7, 2003 in the Gregorian calendar.

In most calendar systems the date consists of three parts: the year, the month and the day of month. There may also be additional parts, such as the day of week. Years are counted from a particular starting point, usually called an era, but sometimes an epoch.

A date with the year part removed may also be referred to as a date or calendar date (e.g. February 7 rather than February 7, 2003). As such it defines the days of an annual festival such as a Birthday or Christmas on December 25th.

Date format

Related to the classification of a day as a specific calendar date, is the format used to express that date.

Even for one calendar system, different formats are used. For example, the following formats all express the same date in the Gregorian calendar:

  • November 16, 2001
  • 11/16/2001 - used in places with American influence. This format was traditional in England, whence it was brought to America. Since the 1900s the English have begun to use the d/m/y format, imported from Europe.
  • 16 November 2001
  • 16/11/2001 or 16.11.2001 or 16-11-2001 - used in places with European influence
  • 2001 November 16
  • 2001-11-16 - the ISO 8601 International standard ordering for dates.

These are further complicated by the common practice of abbreviating the year to its final two digits, and/or abbreviating the full name of the month to its initial three letters.

A significant amount of confusion arises from the ambiguity of a date order; especially with low day, month and/or year numbers, it is impossible to tell which order is being used. Various schemes are used to correct these ambiguities; common schemes include spelling out the month name (or its abbreviation) and using four-digit years. The ISO 8601 date order, with four digit years, is specifically chosen to be unambiguous.

d/m/y (day, month, year) is used by:

m/d/y (month, day, year) is used by:
  • US
  • some traditional UK organisations

y/m/d (year, month, day), the ISO 8601 standard, is used by: See also: calendar, time, date-time group, Japanese calendar, Wikibooks:English:Time