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Date ○꠹｜Definition｜1st｜20251119205401-00-⌔
Calendar date
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 June 2026” is ten days after “15 June 2026”. 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.1 The de facto standard for recording dates worldwide is the Gregorian calendar, the world’s most widely used civil calendar.2 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.3 A date without the year may also be referred to as a date or calendar date (such as “28 June” rather than “28 June 2026”). 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 25 March or Christmas on 25 December.
Printed 2026-06-28.
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Link to original Footnotes
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 following a change of civil calendar used. ↩
Dershowitz, D.; Reingold, E. M (2008). Calendrical Calculations (3rd ed.). Cambridge: Cambridge University Press. p. 45. 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. ↩
For details of the [typically retrospective] calculation of the epoch for each calendar, see their respective articles. ↩
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