ISO 8601 is an international standard for date and time representations issued by the International Organization for Standardization (ISO). Specifically, this standard defines: "Data elements and interchange formats – Information interchange – Representation of dates and times". The signature feature of the ISO 8601 format for date and time is that the information is ordered from the most to the least significant or, in plain terms, from the largest (the year) to the smallest (the second). ... ... Standards are produced by many organizations, some for internal usage only, others for use by a groups of people, groups of companies, or a subsection of an industry. ... A date in a calendar is a reference to a particular day represented within a calendar system. ... A pocket watch, a device used to tell time Look up time in Wiktionary, the free dictionary. ... This article does not cite any references or sources. ... In metadata, the term data element is an atomic unit of data that has: an identification such as a Data element name a clear Data element definition one or more Representation terms optional enumerated values In telecommunication, the term data element has the following components: A named unit of data... This article does not cite any references or sources. ...

History of the standard

The first edition of the ISO 8601 standard was published 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^[1]. It has since then been superseded by a second edition in 2000 and finally the current third edition, ISO 8601:2004, published 2004-12-03. ISO 2014 is a standard superseded by ISO 8601[1]. ISO 2014 was the standard that originally introduced the big-endian all-numeric date notation [YYYY]-[MM]-[DD]. ^ Technical Committee ISO/TC 154, Processes, data elements and documents in commerce, industry and administration. ... ISO 2015 is a standard superseded by ISO 8601[1]. The ISO week numbering system was introduced in ISO 2015. ... ISO 2711 is a standard superseded by ISO 8601[1]. Identification of days by ordinal dates was originally defined in ISO 2711. ... ISO 3307 is a standard superseded by ISO 8601[1]. ^ Technical Committee ISO/TC 154, Processes, data elements and documents in commerce, industry and administration. ... ISO 4031 is a standard superseded by ISO 8601[1]. ^ Technical Committee ISO/TC 154, Processes, data elements and documents in commerce, industry and administration. ... shelby was here 2004 (MMIV) was a leap year starting on Thursday of the Gregorian calendar. ... is the 337th day of the year (338th in leap years) in the Gregorian calendar. ...

ISO 2014 was the standard that originally introduced the big-endian all-numeric date notation [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. In computing, endianness is the byte (and sometimes bit) ordering in memory used to represent some kind of data. ...

It is maintained by ISO/TC 154.

General principles

Date and time values are organized from most to least significant. Each value (e.g. year, month, day, time) has a fixed number of digits which must be padded with leading zeros. For instance, the notation "4:30 a.m." would be written 04:30. As a result, for each of the several formats of dates and times lexicographical order corresponds to chronological order, except for negative years. A leading zero is any zero that proceeds a number string beginning with a non-null value. ... In mathematics, the lexicographical order, or dictionary order, is a natural order structure of the cartesian product of two ordered sets. ...

Representation can be done in one of two formats: A basic format with a minimal number of characters, or an extended format with separators to enhance human readability.^[2] The standard permits a hyphen separator between date elements, and a colon between hours, minutes, and seconds. For example, "2006-01-06" may be written "20060106" without ambiguity. The extended formats are preferred over basic formats because some basic formats are ambiguous.

Any number of fields may be dropped from any of the date and time formats, but the least significant fields must be dropped first. For example, "2004-05" is a valid ISO 8601 date, which indicates the 5th month of the year 2004. This date will never represent the 5th day of some unknown month in 2004.

Finally, the standard supports the addition of a decimal fraction to the smallest time unit, where higher precision is needed.

Dates

The standard uses the leap rule and month sizes of the Gregorian calendar, which is already the de facto standard of international trade. The Gregorian calendar is the most widely used calendar in the world. ... De facto is a Latin expression that means in fact or in practice. It is commonly used as opposed to de jure (meaning by law) when referring to matters of law or governance or technique (such as standards), that are found in the common experience as created or developed without...

Years

ISO 8601 prescribes a four-digit year to avoid the year 2000 problem. Years can also be expanded to greater than four digits and then should be preceded by a plus sign (+). Years before the epoch (year zero) are always preceded by a minus sign (−). The Year 2000 problem (also known as the Y2K problem, the millennium bug, the Y2K Bug or just Y2K) was the result of a practice in early computer program design that caused some date-related processing to operate incorrectly for dates and times on and after January 1, 2000. ... In chronology, an epoch (or epochal date, or epochal event) means an instant in time chosen as the origin of a particular era. ...

For purposes of reference ISO 8601 assigns the number 1875 to the year in which the Convention du Mètre was signed in Paris – a choice that has been criticized^{[citation needed]} for not being reproducible without another calendar. The Convention du Mètre of May 20, 1875 is an international treaty that established what is now known as the SI system of units. ... City flag City coat of arms Motto: Fluctuat nec mergitur (Latin: Tossed by the waves, she does not sink) The Eiffel Tower in Paris, as seen from the esplanade du Trocadéro. ...

The 2000 version of ISO 8601 allowed rendition of a two-digit year (omitting the century), but the 2004 version eliminated that option and requires at least a four-digit year.

Calendar date

Calendar dates are the form familiar to most people. As represented in the box to the right, [YYYY] indicates a year with century. [MM] indicates the month of the year, 01 through 12. [DD] indicates the day of that month, from 01 through 31. For example, "5th of April 1981" may be represented as "1981-04-05" in the extended format, or "19810405" in the basic format.

The standard allows for dates to be written with less precision. For example, one may write "1981-04" to mean "1981 April", and one may simply write "1981" to refer to that year. The standard allows both YYYYMMDD and YYYY-MM-DD; but if the day is omitted, only YYYY-MM is allowed. By disallowing dates of the form YYYYMM, the standard avoids confusion with an alternative 6-digit date representation, YYMMDD, which was common in the 20th century, for example in the case of 102401, which could be understood as 2010-24-01 or 1024-01.

Previous versions of the standard allowed the omission of a century. Thus, 2007-10-20 might be abbreviated to 07-10-20 if the century was obvious. However, the 2004 version of the standard does not allow this, and requires that the year be specified using four or more digits.

Week dates

Main article: ISO week date

A week date specifies a so-called ISO year in the format [YYYY], a week number in the format [WW] prefixed by the letter 'W', and the weekday number, a digit [D] from 1 through 7, beginning with Monday and ending with Sunday. This form is popular in manufacturing. The ISO week date system is a leap week calendar system that is part of the ISO 8601 date and time standard. ...

Mutually equivalent definitions for week 01 are:

• the week with the year's first Thursday in it
• the week with 4 January in it
• the first week with the majority (four or more) of its days in the starting year
• the week starting with the Monday in the period 29 December - 4 January
• 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.

The week number can be described by counting the Thursdays: week 12 contains the 12th Thursday of the year. January 4 is the 4th day of the year in the Gregorian calendar. ... December 29 is the 363rd day of the year (364th in leap years) in the Gregorian calendar, with 2 days remaining. ... January 4 is the 4th day of the year in the Gregorian calendar. ... is the 1st day of the year in the Gregorian calendar. ... is the 1st day of the year in the Gregorian calendar. ...

The ISO 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 ISO year number deviates from the number of the normal year (Gregorian year) on, if applicable, a Friday, Saturday, and Sunday, or a Saturday and Sunday, or just a Sunday, at the start of the ordinary year (which are at the end of the previous ISO year) and a Monday, Tuesday and Wednesday, or a Monday and Tuesday, or just a Monday, at the end of the ordinary year (which are in week 01 of the next ISO year). For Thursdays the ISO year number is always equal to the ordinary year number.

Examples:

• 2008-12-29 is written "2009-W01-1"
• 2010-01-03 is written "2009-W53-7"

For an overview of week numbering systems see week number. The US system has weeks from Sunday through Saturday, and partial weeks at the beginning and the end of the year. An advantage is that no separate year numbering like the ISO year is needed, while correspondence of lexicographical order and chronological order is preserved. For the TV station in the Peoria-Bloomington, Illinois market, see WEEK-TV. A week is a unit of time longer than a day and shorter than a month. ...

Ordinal dates

Ordinal dates are a simple form for times 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 366 in leap years. For example, "1981-04-05" is also "1981-095".

This format has particular use for simple hardware systems that have need of a date system, but where including full calendar calculation software may be a significant nuisance. This system is frequently, though incorrectly, referred to as the Julian Date. The Julian day or Julian day number (JDN) is the number of days that have elapsed since 12 noon Greenwich Mean Time (UT or TT) on Monday, January 1, 4713 BC (in the proleptic Julian calendar; or November 24, 4714 BC in the proleptic Gregorian calendar). ...

Further details about dates

The standard allows for expansion of the year, by agreement between sender and receiver^[3]. Expansion means that the year may be written with more than four digits, which addresses the year 10,000 problem, by allowing the standard to specify dates later than AD 10000 or earlier than 10001 BC. Note however that expansion introduces ambiguities if separators are not used. For instance 200406 could either mean the year 200406 or June 2004. The ISO standard suggests that "provisions be made" to prevent such confusions^{[citation needed]}. This article or section is not written in the formal tone expected of an encyclopedia article. ... (9th millennium – 10th millennium – 11th millennium and beyond – other millennia) The tenth millennium is a period of time which will begin on January 1, 9001 and will end on December 31, 10000. ... Three temperature records, the GRIP one clearly showing the Younger Dryas event at around 11 kyr BP The Younger Dryas stadial, named after the alpine / tundra wildflower Dryas octopetala, and also referred to as the Big Freeze [1], was a brief (approximately 1300 ± 70 years [1]) cold climate period following... 2004 : January - February - March - April - May - June - July - August - September - October - November - December See also: June 2004 in sports Deaths in June • 28 Anthony Buckeridge • 26 Naomi Shemer • 26 Yash Johar • 22 Bob Bemer • 22 Thomas Gold • 22 Francisco Ortiz Franco • 16 Thanom Kittikachorn • 10 Ray Charles • 5 Ronald Reagan...

Times

ISO 8601 uses the 24-hour clock system that is used by most of the world. 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 notate the midnight at the end of a calendar date. [mm] refers to a minute between 00 and 59. [ss] refers to a second between 00 and 59 (or 60 in the exceptional case of an added leap second). So a time might appear as "13:47:30" or "134730". The 24-hour clock is a convention of time-keeping in which the day runs from midnight to midnight and is divided into 24 hours, numbered from 0 to 23. ... The hour (symbol: h) is a unit of time. ... A minute is a unit of time equal to 1/60th of an hour and to 60 seconds. ... Look up second in Wiktionary, the free dictionary. ... A leap second is a one-second adjustment to civil time in order to keep it close to the mean solar time. ...

It is also acceptable to omit elements to reduce precision. [hh]:[mm], [hh][mm] and [hh] are all used.

Decimal fractions may also be used with any of the three time elements. These are indicated by using the decimal point (either a comma (which is preferred ISO 31) or dot). A fraction may only refer to the most precise component of a time representation – that is, to denote "14 hours, 30 and one half minutes", do not include a seconds figure. Represent it as "14:30,5" or "1430,5". The decimal separator is used to mark the boundary between the integer and the fractional parts of a decimal numeral. ... A comma ( , ) is a punctuation mark. ... International Standard ISO 31 (Quantities and units, International Organization for Standardization, 1992) is the most widely respected style guide for the use of units of measurement, and formulas involving them, in scientific and educational documents worldwide. ... This article does not cite any references or sources. ...

Midnight is a special case and can be referred to as both "00:00" and "24:00". The notation "00:00" is used at the beginning of the day, and is the most frequently used one. At the end of a day use "24:00". Note that "1981-04-05T24:00" is the same instant as "1981-04-06T00:00" (see Combined representations below). For other uses, see Midnight (disambiguation) Midnight, literally the middle of the night, is a time arbitrarily designated to determine the end of a day and the beginning of the next in some, mainly Western, cultures. ...

Time zones

If no time zone information is given with a time, the time zone is assumed to be in some conventional local time zone. While it may be safe to assume a local zone when used between two people in the same area, it is ambiguous when used in communication between multiple timezones. It is usually preferable to indicate a time zone using the standard’s notation. A time zone is a region of the Earth that has adopted the same standard time, usually referred to as the local time. ...

UTC

If the time is in UTC, add a 'Z' directly after the time, without a space. "09:30 UTC" is therefore represented as "09:30Z" or "0930Z". "14:45:15 UTC" would be "14:45:15Z" or "144515Z". Coordinated Universal Time (UTC) is a high-precision atomic time standard. ...

Other time zones

Other time zones are specified by their offset from UTC, in the format ±[hh]:[mm], ±[hh][mm] or ±[hh]. So if the time being described is one hour ahead of UTC (such as the time in Berlin during the winter) the offset would be "+01:00", "+0100" or simply "+01". This is appended to the time in the same way that 'Z' was above. Note that the offset is the actual offset from UTC, and does not include any information on daylight saving time. Times expressed in local time for a user in Chicago would be "-06:00" for the winter (Central Standard Time) and "-05:00" for the summer (Central Daylight Time). The following times all refer to the same moment: "18:30Z", "22:30+04", "1130-0700" and "15:00-03:30". Nautical time zone letters are not used, with the exception of Z. This article is about the capital of Germany. ... Though DST is common in Europe and North America, most of the worlds people do not use it. ... Nickname: Motto: Urbs In Horto (Latin: City in a Garden), I Will Location in the Chicago metro area and Illinois Coordinates: , Country United States State Illinois County Cook & DuPage Settled 1770s Incorporated March 4, 1837 Government  - Mayor Richard M. Daley (D) Area  - City  234. ...  CST or UTC-6 The Central Standard Time Zone (CST) is a geographic region in the Americas that keeps time by subtracting six hours from UTC (UTC-6). ... The Central Standard Time Zone (CST) is a geographic region that keeps time by subtracting six hours from UTC (UTC-6). ...

Time zone conversions

A possible source of confusion in doing time zone conversions is the ISO committee's decision to create time expressions using offsets from UTC rather than to UTC (i.e., having opposite sign). While a time expression looks like a conversion formula yielding its UTC value, it is not. Reverse the sign in the expression, however, and it is. Referring to the above examples, we see that 18:30 (UTC) = 22:30 - 04:00 = 11:30 + 07:00 = 15:00 + 3:30.

Conversion between time zones obeys the relationship

"time in zone A" + "offset from zone A to UTC" = "time in zone B" + "offset from zone B to UTC",

in which each side of the equation is its UTC value (note the phrases "offset from zone" rather than "offset from UTC").

Using the term "offset" as the Standard does (converting the above additions to subtractions), the conversion equation is

"time in zone B" = "time in zone A" - "offset from UTC to zone A" + "offset from UTC to zone B".

For example, what time is it in Los Angeles when the New York Stock Exchange opens?

if (X PST = xxxx-08) = (09:30 EST = 0930-05)

then X = 09:30 -(-05:00) +(-08:00) = 06:30

so (6:30 PST = 0630-08) = (09:30 EST = 0930-05).

Combined representations

Combining date and time representations is quite simple. It is in the format of <date>T<time>. The date and time sections are any proper representation of the date and time created by following the standard. A common use could be [YYYY]-[MM]-[DD]T[hh]:[mm]:[ss]±[hh]:[mm]. "1981-04-05T14:30:30-05:00" or [YYYY][MM][DD]T[hh][mm][ss]Z. "19810405T193030Z", for example.

The date and time representations may sometimes appear in proximity, separated by a space or other characters, in which case they occupy two separate fields in a data system, rather than a single combined representation. This is sometimes done for human readability. Unlike the above example, "1981-04-05" "14:30:30-05:00" are two separate representations, one for date and the other for time.

Duration

Durations are represented by the format P[n]Y[n]M[n]DT[n]H[n]M[n]S (or P[n]Y[n]W[n]DT[n]H[n]M[n]S to use the week format). In this representation replace [n] with the appropriate number for the element that follows it (leading zeros are optional but may clarify ambiguous durations). The capital letters ('P', 'Y', 'M', 'W', 'D', 'T', 'H', 'M' and 'S') are used as they are and not replaced. Thus "P3Y6M4DT12H30M0S" defines "a period of three years, six months, four days, twelve hours, thirty minutes, and zero seconds". Elements may be omitted if their value is zero. To resolve ambiguity, "P1M" is one month and "PT1M" is one minute. The smallest value used may also have a decimal fraction, as in "P0,5Y" to indicate half a year.

Sometimes ISO 8601 is called the "metric date format", but the chosen abbreviations in durations do not match common metric symbols (a, mon, d, h, min, s).

Alternately, a format more based on the combined representation may be used: P[YYYY]-[MM]-[DD]T[hh]:[mm]:[ss]. To represent the same duration as above in this format, use "P0003-06-04T12:30:00".

Time interval

Time intervals specify an amount of time. They may be specified in four ways:

1. Start and end, such as "2002-03-01T13:00:00Z/2003-05-11T15:30:00Z"
2. Start and duration, such as "2002-03-01T13:00:00Z/P1Y2M10DT2H30M"
3. Duration and end, such as "P1Y2M10DT2H30M/2003-05-11T15:30:00Z"
4. Duration only, such as "P1Y2M10DT2H30M"

Of these, the first three require two separate values, separated by the interval designator, which is usually a forward slash "/". In certain application areas a double hyphen (--) is used as a separator instead of a solidus. (Section 4.4.2) An example using the format from item #1 is "1981-04-05T14:30:30-05:00/2004-07-14T15:30:30-05:00". If any elements are missing from the second value, they are assumed to be the same as the first value, including time zone elements. A slash or stroke, /, is a punctuation mark. ... Solidus (Latin) is the name of a Roman coin during the Roman Empire. ...

Repeating intervals

Repeating intervals are formed by adding "R[n]/" to the beginning of an interval expression, where 'R' is used as the letter itself and [n] is replaced by the number of repetitions. Leaving out the value for [n] means an unbounded number of repetitions. So, to repeat the interval of "P1Y2M10DT2H30M" five times starting at "2002-03-01T13:00:00Z", use "R5/2002-03-01T13:00:00Z/P1Y2M10DT2H30M".

Notes

1. ^ Technical Committee ISO/TC 154, Processes, data elements and documents in commerce, industry and administration. (2004-12-01). ISO 8601:2004(E). ISO. Retrieved on 2006-11-15. “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.”
2. ^ Numeric representation of Dates and Time
3. ^ Technical Committee ISO/TC 154, Processes, data elements and documents in commerce, industry and administration. (2004-12-01). ISO 8601:2004(E). ISO. Retrieved on 2006-11-15. “3.5 Expansion … By mutual agreement of the partners in information interchange, it is permitted to expand the component identifying the calendar year, which is otherwise limited to four digits. This enables reference to dates and times in calendar years outside the range supported by complete representations, i.e. before the start of the year [0000] or after the end of the year [9999].”

ISO has many meanings: Iso is the stem of the Latin transliteration of the Greek word ίσος (ísos, meaning equal). The iso- prefix in English derives from this and means equality or similarity. ... For the Manfred Mann album, see 2006 (album). ... is the 319th day of the year (320th in leap years) in the Gregorian calendar. ... ISO has many meanings: Iso is the stem of the Latin transliteration of the Greek word ίσος (ísos, meaning equal). The iso- prefix in English derives from this and means equality or similarity. ... For the Manfred Mann album, see 2006 (album). ... is the 319th day of the year (320th in leap years) in the Gregorian calendar. ...

See also

• Date and time notation by country
• ISO 8601 usage
• Template:ISO8601
• RFC 3339, Date and Time on the Internet, 2002-July

Different stylistic conventions and habits exist around the world in order to express date and time in written and spoken language. ... On the Internet, the World Wide Web Consortium (W3C) uses ISO 8601 in defining a profile of the standard that restricts the supported date and time formats to reduce the chance of error and the complexity of software. ...

External links

• ISO 8601:2004(E) from ISO (zip-pdf, 228KB)
• Summary of 8601 by ISO
• Technical Committee ISO/TC 154, Processes, data elements and documents in commerce, industry and administration.
• ISO 8601 summary by Markus Kuhn
• The Mathematics of the ISO 8601 Calendar
• Current date in week date and ordinal date format
• ISO 8601 at the Open Directory Project
• W3C Specification about UTC Date and Time and IETF Internet standard RFC 3339, based on ISO 8601

The Open Directory Project (ODP), also known as dmoz (from , its original domain name), is a multilingual open content directory of World Wide Web links owned by Netscape that is constructed and maintained by a community of volunteer editors. ... The Internet Engineering Task Force (IETF) is charged with developing and promoting Internet standards. ... An Internet standard is a specification for an innovative internetworking technology or methodology, which the Internet Engineering Task Force (IETF) ratified as an open standard after the innovation underwent peer review. ...

Implementations

• Converting and implementing
• An implementation in Java (Joda-Time)
• A reference implementation in JavaScript