ISO 8601

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ISO 8601
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]| label1 = Date| data1 = {{ISO date}}| label2 = Date and time in UTC{{#time:c}}}}{{#time: Y-m-d"T"H:i:s"Z"}}{{#time: Ymd"T"His"Z"}}| label3 = Week| data3 = {{#time: o-"W"W}}| label4 = Date with week number| data4 = {{#time: o-"W"W-N}}| label5 = Date without year{{#time: --m-d}}|ISO}}last in ISO8601:2000, in use by WEB
, RFC 6350 - vCard Format Specification
, 2016-06-29
, August 2011
, Internet Engineering Task Force, IETF
, Truncated representation, as specified in [ISO.8601.2000], Sections d), e), and f), is permitted., | label6 = Ordinal date
3}}}}ISO 8601 Data elements and interchange formats – Information interchange – Representation of dates and times is an international standard covering the exchange of date- and time-related data. It was issued by the International Organization for Standardization (ISO) and was first published in 1988. The purpose of this standard is to provide an unambiguous and well-defined method of representing dates and times, so as to avoid misinterpretation of numeric representations of dates and times, particularly when data are transferred between countries with different conventions for writing numeric dates and times.In general, ISO 8601 applies to representations and formats of dates in the Gregorian (and potentially proleptic Gregorian) calendar, of times based on the 24-hour timekeeping system (with optional UTC offset), of (Time interval#Time-like concepts: terminology|time intervals), and combinations thereof.ISO 8601:2004[E] section 1 Scope The standard does not assign any specific meaning to elements of the date/time to be represented; the meaning will depend on the context of its use. In addition, dates and times to be represented cannot include words with no specified numerical meaning in the standard (e.g., names of years in the Chinese calendar) or that do not use characters (e.g., images, sounds).In representations for interchange, dates and times are arranged so the largest temporal term (the year) is placed to the left and each successively smaller term is placed to the right of the previous term. Representations must be written in a combination of Arabic numerals and certain characters (such as "-", ":", "T", "W", and "Z") that are given specific meanings within the standard; the implication is that some commonplace ways of writing parts of dates, such as "January" or "Thursday", are not allowed in interchange representations.


The first edition of the ISO 8601 standard was published as ISO 8601:1988 in 1988. It unified and replaced a number of older ISO standards on various aspects of date and time notation: ISO 2014, ISO 2015, ISO 2711, ISO 3307, and ISO 4031.{{citation
|title=ISO 8601:2004(E)
|quote=Annex A ... From that concept representations of all other date and time values were logically derived; thus, ISO 2014, ISO 3307 and ISO 4031 have been superseded.... Identification of a particular date by means of ordinal dates (ISO 2711) and by means of the week numbering system (ISO 2015) were alternative methods that the basic concept of this International Standard could also encompass; thus, ISO 2015 and ISO 2711 have now been superseded.}} It has been superseded by a second edition ISO 8601:2000 in 2000 and by the current third edition ISO 8601:2004 published on 2004-12-01. ISO 8601 was prepared by,BOOK, ISO 8601:2004(E), 2004-12-01, International Organization for Standardization, ISO, p. iv Foreword, and is under the direct responsibility of, ISO Technical Committee TC 154.TC 154 Processes, data elements and documents in commerce, industry and administration, Technical committees{{spaced ndash}}ISO
ISO 2014, though superseded, is the standard that originally introduced the all-numeric date notation in most-to-least-significant order {{nowrap|[YYYY]-[MM]-[DD]}}. The ISO week numbering system was introduced in ISO 2015, and the identification of days by ordinal dates was originally defined in ISO 2711.{{anchor|EDTF}}ISO 8601 is currently in the process of being updated and split into two parts anticipated to be released in {{Update after|2019|03|reason=working draft's schedule|text=2019-03}}. The draft ISO/DIS 8601-1:2016 represents the slightly updated contents of the current ISO 8601 standard,weblink" title="">ISO/DIS 8601-1:2016-10-26German draft E DIN ISO 8601-1:2017-02 Datenelemente und Austauschformate - Informationsaustausch - Darstellung von Datum und Uhrzeit - Teil 1: Grundlegende Regeln (ISO/DIS 8601-1:2016), DIN-Normenausschuss Informationstechnik und Anwendungen (NIA) whereas the draft ISO/DIS 8601-2:2016 defines various extensions such as uncertainties or parts of the Extended Date/Time Format (EDTF).ISO/WD 8601-2:2016-02-16ISO/DIS 8601-2:2016-10-26German draft E DIN ISO 8601-2:2017-02 Datenelemente und Austauschformate - Informationsaustausch - Darstellung von Datum und Uhrzeit - Teil 2: Erweiterungen (ISO/DIS 8601-2:2016), DIN-Normenausschuss Informationstechnik und Anwendungen (NIA)EDTFExtended Date/Time Format (EDTF) 1.0 2012/2014 Draft Submission

General principles

  • Date and time values are ordered from the largest to smallest unit of time: year, month (or week), day, hour, minute, second, and fraction of second. The lexicographical order of the representation thus corresponds to chronological order, except for date representations involving negative years. This allows dates to be naturally sorted by, for example, file systems.
  • Each date and time value has a fixed number of digits that must be padded with leading zeros.
  • Representations can be done in one of two formats{{spaced ndash}}a basic format with a minimal number of separators or an extended format with separators added to enhance human readability.ISO, FAQ: Numeric representation of Dates and Time"Date and Time Formats". The standard notes that "The basic format should be avoided in plain text."ISO 8601:2004 section 2.3.3 basic format The separator used between date values (year, month, week, and day) is the hyphen, while the colon is used as the separator between time values (hours, minutes, and seconds). For example, the 6th day of the 1st month of the year 2009 may be written as {{nowrap|"2009-01-06"}} in the extended format or simply as "20090106" in the basic format without ambiguity.
  • For reduced accuracy,ISO 8601 uses the word accuracy, not precision, in the relevant section, e.g: 2.3.7 representation with reduced accuracy. any number of values may be dropped from any of the date and time representations, but in the order from the least to the most significant. For example, "2004-05" is a valid ISO 8601 date, which indicates May (the fifth month) 2004. This format will never represent the 5th day of an unspecified month in 2004, nor will it represent a time-span extending from 2004 into 2005.
  • If necessary for a particular application, the standard supports the addition of a decimal fraction to the smallest time value in the representation.


{{ISOCALENDAR}}The standard uses the Gregorian calendar, which serves as an international standard for civil use.BOOK
, Doggett
, L. E.
, P. K. Seidelmann
, 1992
, University Science Books
, Explanatory Supplement to the Astronomical Almanac
, Sausalito, California
, 0-935702-68-7
, 580
, Calendars
, The Gregorian calendar today serves as an international standard for civil use.
, yes
,weblink" title="">weblink
, 2004-04-01
, ISO 8601 fixes a reference calendar date to the Gregorian calendar of 20 May 1875 as the date the (Metre Convention) was signed in Paris. However, ISO calendar dates before the Convention are still compatible with the Gregorian calendar all the way back to the official introduction of the Gregorian calendar on {{nowrap|1582-10-15}}. Earlier dates, in the proleptic Gregorian calendar, may be used by mutual agreement of the partners exchanging information. The standard states that every date must be consecutive, so usage of the Julian calendar would be contrary to the standard (because at the switchover date, the dates would not be consecutive).

Years{| class"infobox" style"text-align:center; width:23em"

| YYYY| ±YYYYYISO 8601 prescribes, as a minimum, a four-digit year [YYYY] to avoid the year 2000 problem. It therefore represents years from 0000 to 9999, year 0000 being equal to 1 BC and all others AD. However, years prior to 1583 are not automatically allowed by the standard. Instead "values in the range [0000] through [1582] shall only be used by mutual agreement of the partners in information interchange."BOOK, ISO 8601:2004(E), 2004-12-01International Organization for Standardization>ISO, section General, To represent years before 0000 or after 9999, the standard also permits the expansion of the year representation but only by prior agreement between the sender and the receiver.BOOK, ISO 8601:2004(E), 2004-12-01International Organization for Standardization>ISOAnno Domini>AD/BC (or Common Era) notation; by convention 1 BC is labelled year zero>+0000, 2 BC is labeled −0001, and so on.For example, see Annex B.1.1 of the standard.

Calendar dates{| class"infobox" style"text-align:center; width:23em"

or>| YYYYMMDD| YYYY-MM (but not YYYYMM)or>| --MMDDCalendar date representations are in the form shown in the adjacent box. [YYYY] indicates a four-digit year, 0000 through 9999. [MM] indicates a two-digit month of the year, 01 through 12. [DD] indicates a two-digit day of that month, 01 through 31. For example, "5 April 1981" may be represented as either {{nowrap|"1981-04-05"}} in the extended format or "19810405" in the basic format.The standard also allows for calendar dates to be written with reduced accuracy. For example, one may write {{nowrap|"1981-04"}} to mean "1981 April". The 2000 version allowed writing {{nowrap|"--04-05"}} to mean "April 5"WEB
, RFC 6350 - vCard Format Specification
, 2016-06-29
, August 2011
, Internet Engineering Task Force, IETF
, Truncated representation, as specified in [ISO.8601.2000], Sections d), e), and f), is permitted., but the 2004 version does not allow omitting the year when a month is present. One may simply write "1981" to refer to that year or "19" to refer to the century from 1900 to 1999 inclusive. Although the standard allows both the YYYY-MM-DD and YYYYMMDD formats for complete calendar date representations, if the day [DD] is omitted then only the {{nowrap|YYYY-MM}} format is allowed. By disallowing dates of the form YYYYMM, the standard avoids confusion with the truncated representation YYMMDD (still often used).

Week dates

{| class="infobox" style="text-align:center; width:23em"or>| YYYYWwwor>| YYYYWwwDWeek date representations are in the formats as shown in the adjacent box. [YYYY] indicates the ISO week-numbering year which is slightly different from the traditional Gregorian calendar year (see below). [Www] is the week number prefixed by the letter W, from W01 through W53. [D] is the weekday number, from 1 through 7, beginning with Monday and ending with Sunday.There are several mutually equivalent and compatible descriptions of week 01:
  • the week with the year's first Thursday in it (the formal ISO definition),
  • the week with 4 January in it,
  • the first week with the majority (four or more) of its days in the starting year, and
  • the week starting with the Monday in the period 29 December – 4 January.
As a consequence, if 1 January is on a Monday, Tuesday, Wednesday or Thursday, it is in week 01. If 1 January is on a Friday, Saturday or Sunday, it is in week 52 or 53 of the previous year (there is no week 00). 28 December is always in the last week of its year.The week number can be described by counting the Thursdays: week 12 contains the 12th Thursday of the year.The ISO week-numbering year starts at the first day (Monday) of week 01 and ends at the Sunday before the new ISO year (hence without overlap or gap). It consists of 52 or 53 full weeks. The first ISO week of a year may have up to three days that are actually in the Gregorian calendar year that is ending; if three, they are Monday, Tuesday and Wednesday. Similarly, the last ISO week of a year may have up to three days that are actually in the Gregorian calendar year that is starting; if three, they are Friday, Saturday, and Sunday. The Thursday of each ISO week is always in the Gregorian calendar year denoted by the ISO week-numbering year.Examples:
  • {{time: l j F Y |2008-12-29}} is written "{{time: o-"W"W-N|2008-12-29}}"
  • {{time: l j F Y |2010-01-03}} is written "{{time: o-"W"W-N|2010-01-03}}"
or>| YYYYDDD">

Ordinal dates{| class"infobox" style"text-align:center; width:23em"or>| YYYYDDD

An ordinal date is a simple form for occasions when the arbitrary nature of week and month definitions are more of an impediment than an aid, for instance, when comparing dates from different calendars. As represented above, [YYYY] indicates a year. [DDD] is the day of that year, from 001 through 365 (366 in leap years). For example, {{nowrap|"1981-04-05"}} is also {{nowrap|"1981-095"}}.This format is used with simple hardware systems that have a need for a date system, but where including full calendar calculation software may be a significant nuisance. This system is sometimes referred to as "Julian Date", but this can cause confusion with the astronomical Julian day, a sequential count of the number of days since day 0 beginning {{nowrap|1 January 4713 BC}} Greenwich noon, Julian proleptic calendar (or noon on ISO date {{nowrap|-4713-11-24}} which uses the Gregorian proleptic calendar with a year [0000]).or|hhmmss.sssor>| hhmmss">

Times{| class"infobox" style"text-align:center; width:23em"|hh:mm:ss.sss|or|hhmmss.sssor>| hhmmss

or>| hhmm|ISO 8601 uses the 24-hour clock system. The basic format is [hh][mm][ss] and the extended format is [hh]:[mm]:[ss].
  • [hh] refers to a zero-padded hour between 00 and 24 (where 24 is only used to denote midnight at the end of a calendar day).
  • [mm] refers to a zero-padded minute between 00 and 59.
  • [ss] refers to a zero-padded second between 00 and 60 (where 60 is only used to denote an added leap second).
So a time might appear as either "134730" in the basic format or "13:47:30" in the extended format.Either the seconds, or the minutes and seconds, may be omitted from the basic or extended time formats for greater brevity but decreased accuracy: [hh]:[mm], [hh][mm] and [hh] are the resulting reduced accuracy time formats.ISO 8601:2004 section Representations with reduced accuracyMidnight is a special case and may be referred to as either "00:00" or "24:00". The notation "00:00" is used at the beginning of a calendar day and is the more frequently used. At the end of a day use "24:00". "2007-04-05T24:00" is the same instant as "2007-04-06T00:00" (see Combined date and time representations below).Decimal fractions may be added to any of the three time elements. However, a fraction may only be added to the lowest order time element in the representation. A decimal mark, either a comma or a dot (without any preference as stated in resolution 10 of the 22nd General Conference CGPM in 2003,WEB
, NIST TechBeat 2006-11-22
, 2017-09-27
, 2006-11-22
, National Institute of Standards and Technology, NIST
, Decimals Score a Point on International Standards ... It soon may be possible to write international standards documents with decimal points in them., but with a preference for a comma according to ISO 8601:2004){{citation
|title=ISO 8601:2004(E)
|quote= ... the decimal fraction shall be divided from the integer part by the decimal sign specified in ISO 31-0, i.e. the comma [,] or full stop [.]. Of these, the comma is the preferred sign.}} is used as a separator between the time element and its fraction. To denote "14 hours, 30 and one half minutes", do not include a seconds figure. Represent it as "14:30,5", "1430,5", "14:30.5", or "1430.5". There is no limit on the number of decimal places for the decimal fraction. However, the number of decimal places needs to be agreed to by the communicating parties. For example, in Microsoft SQL Server, the precision of a decimal fraction is 3, i.e., "yyyy-mm-ddThh:mm:ss[.mmm]".WEB,weblink ISO 8601 Format,, en, 2017-10-16,

Time zone designators

{| class="infobox" style="text-align:center; width:23em"|
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