International standards are standards developed by international standards organisations. International standards are available for consideration and use, worldwide.... for date
Calendar date
A date in a calendar is a reference to a particular day represented within a calendar system. The calendar date allows the specific day to be identified.... and time
Time
Time is a component of the measurement used to sequence events, to compare the durations of events and the intervals between them, and to quantify the motions of objects.... representations issued by the International Organization for Standardization
International Organization for Standardization
The International Organization for Standardization , widely known as ISO , is an international standard-setting body composed of representatives from various national standards organizations.... (ISO). Specifically, the standard is titled "Data element
Data element
In metadata, the term data element is an atomic unit of data that has precise meaning or precise semantics. A data element has:# An identification such as a data element name... s and interchange formats — Information interchange — Representation of dates and times". The signature feature of ISO
International Organization for Standardization
The International Organization for Standardization , widely known as ISO , is an international standard-setting body composed of representatives from various national standards organizations.... 8601 date and time representations is the ordering of date and time values from the most to the least significant or, in plain terms, from the largest (the year) to the smallest (the second).
first edition of the ISO 8601 standard was published in 1988.
International standards are standards developed by international standards organisations. International standards are available for consideration and use, worldwide.... for date
Calendar date
A date in a calendar is a reference to a particular day represented within a calendar system. The calendar date allows the specific day to be identified.... and time
Time
Time is a component of the measurement used to sequence events, to compare the durations of events and the intervals between them, and to quantify the motions of objects.... representations issued by the International Organization for Standardization
International Organization for Standardization
The International Organization for Standardization , widely known as ISO , is an international standard-setting body composed of representatives from various national standards organizations.... (ISO). Specifically, the standard is titled "Data element
Data element
In metadata, the term data element is an atomic unit of data that has precise meaning or precise semantics. A data element has:# An identification such as a data element name... s and interchange formats — Information interchange — Representation of dates and times". The signature feature of ISO
International Organization for Standardization
The International Organization for Standardization , widely known as ISO , is an international standard-setting body composed of representatives from various national standards organizations.... 8601 date and time representations is the ordering of date and time values from the most to the least significant or, in plain terms, from the largest (the year) to the smallest (the second).
Example date:
--
Example separate date and time in UTC:
-- Z
Example combined date and time in UTC:
--TZ
Example date with week number:
Example ordinal date:
-
History
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 2014
ISO 2014 is a standard superseded by ISO 8601. ISO 2014 was the standard that originally introduced the big-endian all-numeric date notation [YYYY]-[MM]-[DD].... , ISO 2015
ISO 2015
ISO 2015 is a standard superseded by ISO 8601. The ISO week numbering system was introduced in ISO 2015. It was issued as an international standard in 1976, technically identical to ISO Recommendation R 2015 from 1971.... , ISO 2711
ISO 2711
ISO 2711 is a standard superseded by ISO 8601. Identification of days by ordinal dates was originally defined in ISO 2711. It was issued in 1973.... , ISO 3307
ISO 3307
ISO 3307 is a standard superseded by ISO 8601. Representations of time of the day were originally specified in ISO 3307. The standard was issued in 1975.... , and ISO 4031
ISO 4031
ISO 4031 is a standard superseded by ISO 8601. Representations of local time differentials were originally specified in ISO 4031. The standard was issued in 1978.... . It has been superseded by a second edition in 2000 and by the current third edition, , published 2004-12-03.
ISO 2014 was the standard that originally introduced the big-endian
Endianness
In computing, endianness is the byte ordering used to represent some kind of data. Typical cases are the order in which integer values are stored as bytes in computer memory and the transmission order over a network or other medium.... 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.
It is maintained by ISO Technical Committee .
Scope and application of the standard
The scope of the standard covers representations for Gregorian dates, time of day, combined date and time of day, and time intervals. Dates can be represented in three forms: 1) year-month-day of month, 2) year-week number-day of week, and 3) year-day of year. Time of day is represented by using the 24-hour clock
24-hour clock
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.... . Combined date and time is represented by merging both the date and time of day representations to denote a single time point. Time intervals are represented in a number of ways by using a combination of a start point, end point, duration, and context information.
The application of the standard is intended to be very broad. It applies to all written communications that contain dates, times, and time intervals regardless of the communication medium (printed, electronic, or hand written) or the location of the sender and receiver (either within an organization, between organizations, or across international boundaries). The application of the standard was never meant to be limited to dates and times processed, stored, and displayed by computers. It applies to all industries and all forms of human activity where accurate and unambiguous representations of dates, times, and time intervals are needed when communicating internationally, nationally, locally, internally, or even privately.
The standard does not cover worded dates, nor does it preclude the use of worded dates. Worded dates are specifically omitted from the standard mostly because their language dependency can impede international communication.
General principles
Date and time values are organized from the most to the least significant: year, month (or week), day, hour, minute, second, and fraction of second. The lexicographical order
Lexicographical order
In mathematics, the lexicographic or lexicographical order, , is a natural order theory structure of the Cartesian product of two ordered sets.... of the representation corresponds to chronological order, except for date representations involving negative years.
Each date and time value has a fixed number of digits that must be padded with leading zero
Leading zero
A leading zero is any 0 that leads a number string with a non-zero value. For example, James Bond's famous identifier, 007, has two leading zeros.... s.
Representations can be done in one of two formats—a basic format with a minimal number of separators or an extended format with separators added to enhance human readability. The separator used between date values (year, month, week, and day) is the hyphen
Hyphen
A hyphen is a punctuation mark. It is used both to join words and also to separate syllables of a single word. It is often confused with the dash , which are longer and have different uses, and with the minus sign which is also longer.... , while the colon
Colon (punctuation)
The colon is a punctuation mark, consisting of two equally sized dots centered on the same vertical line.... 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 "2009-01-06" in the extended format or simply as "20090106" in the basic format without ambiguity. The extended formats are preferred over the basic formats not only for human readability, but because some basic formats can appear to be ambiguous to those unfamiliar with the standard.
For 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 the 5th month of the year 2004. This date will never represent the 5th day of some unknown month in 2004.
When higher precision is needed, the standard supports the addition of a decimal fraction to the smallest time value in the representation.
The Gregorian calendar is the internationally accepted civil calendar. It was first proposed by the Calabrian doctor Aloysius Lilius, and decreed by Pope Gregory XIII, after whom it was named, on 24 February 1582 by the papal bull Inter gravissimas.... , which is the most widely used calendar in the world and is already the de facto standard
De facto
De facto is a Latin expression that means "concerning the fact" or in practice but not necessarily ordained by law. It is commonly used in contrast to de jure when referring to matters of law, governance, or technique that are found in the common experience as created or developed without or contrary to a regulation.... of international trade.
As a point of interest, ISO 8601 fixes a reference calendar date to the Gregorian calendar of 1875-05-20 as the date the Convention du Mètre (Metre Convention) was signed in Paris
Paris
Paris is the Capital of France and the country's largest city. It is situated on the river Seine, in northern France, at the heart of the ?le-de-France Regions of France .... . 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 1582-10-15. Earlier dates, in the proleptic Gregorian calendar
Proleptic Gregorian calendar
The proleptic Gregorian calendar is produced by extending the Gregorian calendar backward to dates preceding its official introduction in 1582.... , may be used by mutual agreement of the partners exchanging information.
Years
YYYY
±YYYYY
ISO 8601 prescribes, as a minimum, a four-digit year [YYYY] to avoid the year 2000 problem
Year 2000 problem
The Year 2000 problem was a notable computer bug resulting from the practice in early computer program design of representing the year with two digits.... .
Year zero is not used in the widely used Gregorian calendar, nor in its predecessor, the Julian calendar. Under those systems, the year 1 BC is followed by AD 1.... or after 9999
Year 10,000 problem
The Year 10,000 problem, or Y10K, is the class of all potential software bugs that may emerge should the need to express years with five digits arise.... , the standard also permits the expansion of the year representation [±YYYYY], but only by prior agreement between the sender and the receiver. An expanded year representation must have an agreed upon number of extra year digits beyond the four-digit minimum and is always prefixed with a + or − sign with the convention that year 0 is positive.
The common BC notation, for dates that are before year 0001, is not used. For instance, the year 3 BC can be denoted by -0002. (There is a difference of 1 because the BC system has no year zero.)
Calendar dates
YYYY-MM-DD
or
YYYYMMDD
YYYY-MM
(but not YYYYMM)
Calendar date representations are in the form as shown in the box to the right. [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, "the 5th of April 1981" may be represented as either "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 precision. For example, one may write "1981-04" to mean "1981 April", and one may simply write "1981" to refer to that year or "19" to refer to that century.
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 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
YYYY-Www
or
YYYYWww
YYYY-Www-D
or
YYYYWwwD
Week date representations are in the format as shown in the box to the right. [YYYY] indicates the ISO week-numbering year which is slightly different to the 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. This form is popular in the manufacturing industries.
There are mutually equivalent 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.
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. 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 ISO week-numbering year number deviates from the number of the calendar year (Gregorian year) on a Friday, Saturday, and Sunday, or a Saturday and Sunday, or just a Sunday, at the start of the calendar year (which are at the end of the previous ISO week-numbering year) and a Monday, Tuesday and Wednesday, or a Monday and Tuesday, or just a Monday, at the end of the calendar year (which are in week 01 of the next ISO week-numbering year). For Thursdays, the ISO week-numbering year number is always equal to the calendar year number.
Examples:
2008-12-29 is written ""
2010-01-03 is written ""
For an overview of week numbering systems see week number
Week
A week is a grouping of days or a division of a larger grouping such as a lunar month, year, etc. The week allows for shorter routine than a month and benefits groups of people with organising market days, worship, taxes, etc.... . 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 week-numbering year is needed, while correspondence of lexicographical order and chronological order is preserved.
An ordinal date is a calendar date consisting of a year and a day of year ranging between 1 and 366 . The two numbers can be formatted as YYYY-DDD to comply with the ISO 8601#Ordinal dates format.... 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 year
Leap year
A leap year is a year containing one or more extra days in order to keep the calendar year synchronized with the astronomical year or seasonal year.... s). 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 sometimes incorrectly referred to as "Julian Date", while the astronomical Julian Date
Julian day
The Julian date is the interval of time in days and fractions of a day, since January 1, 4713 BC Greenwich noon, Julian proleptic calendar. In precise work, the timescale, e.g., Terrestrial Time or Universal Time , should be specified.... is a straight leap number date originating from January 1, 4713 BC Greenwich noon, Julian proleptic calendar.
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.... system. The basic format is [hh][mm][ss] and the extended format is [hh]:[mm]:[ss].
The hour is a unit of time. It is not an SI unit but is Non-SI units accepted for use with SI.... between 00 and 24, where 24 is only used to notate the midnight at the end of a calendar day.
A minute is a unit of measurement of time or of angle.The minute is a Unit of measurement of time equal to 1/60th of an hour or 60 seconds. In the Coordinated Universal Time time scale, a minute occasionally has 59 or 61 seconds; see leap second.... between 00 and 59.
The second , sometimes abbreviated sec., is the name of a units of measurement of time, and is the International System of Units SI base unit of time.... between 00 and 59 (or 60 in the exceptional case of an added leap second
Leap second
A leap second is a plus or minus one-second adjustment to the Coordinated Universal Time time scale that keeps it close to Solar time. UTC, which is used as the basis for official time-of-day radio broadcasts for civil time, is maintained using extremely precise atomic clocks.... ).
So a time might appear as either "134730" in the basic format or "13:47:30" in the extended format.
It is also acceptable to omit lower order time elements for reduced accuracy: [hh]:[mm], [hh][mm] and [hh] are all used.
Midnight is, literally, "the middle of the night." In most systems it is when one day ends and the next begins: when the date changes. Originally midnight was halfway between sunset and dawn, varying according to the seasons.... 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 a calendar day and is the more frequently used. At the end of a day use "24:00". Note that "2007-04-05T24:00" is the same instant as "2007-04-06T00:00" (see Combined date and time representations below).
Decimal fractions may also be added to any of the three time elements. A decimal point, either a comma
Comma (punctuation)
The comma is a punctuation mark. It has the same shape as an apostrophe or single closing quotation mark in many typefaces, but it differs from them in being placed on the baseline of the text.... or a dot
Full stop
A full stop or period , is the punctuation mark commonly placed at the end of several different types of Sentence s in English language and many other languages.... (without any preference as stated most recently in resolution 10 of the 22nd General Conference CGPM in 2003), is used as a separator between the time element and its fraction. A fraction may only be added to the lowest order time element in the representation. To denote "14 hours, 30 and one half minutes", do not include a seconds figure. Represent it as "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.
A time zone is a region of the earth that has uniform standard time, usually referred to as the local time. By convention, time zones compute their local time as an offset from Coordinated Universal Time .... information is given with a time representation, the time is assumed to be in local time. While it may be safe to assume local time when communicating in the same time zone, it is ambiguous when used in communicating across different time zones. It is usually preferable to indicate a time zone (zone designator) using the standard’s notation.
Coordinated Universal Time is a time standard based on International Atomic Time with leap seconds added at irregular intervals to compensate for the Earth's slowing rotation.... , add a 'Z' directly after the time without a space. 'Z' is the zone designator for the zero UTC offset. "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 is a time standard based on International Atomic Time with leap seconds added at irregular intervals to compensate for the Earth's slowing rotation.... time is also known as 'Zulu' time, since 'Zulu' is the NATO phonetic alphabet
NATO phonetic alphabet
The NATO phonetic alphabet, more formally the international radiotelephony spelling alphabet, is the most widely used spelling alphabet. Though often called "phonetic alphabets", spelling alphabets have no connection to phonetic transcription systems like the International Phonetic Alphabet.... word for 'Z'.
Other time zones
The zone designator for other time zones is specified by the 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
Berlin
Berlin is the Capital of Germany city and one of sixteen States of Germany of Germany. With a population of 3.4 million within its city limits, Berlin is the country's largest city.... during the winter), the zone designator 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 zone designator is the actual offset from UTC and does not include any information on daylight saving time
Daylight saving time
Daylight saving time is the convention of advancing clocks so that afternoons have more daylight and mornings have less. Typically clocks are adjusted forward one hour near the start of spring and are adjusted backward in autumn.... . The zone designator or UTC offset for a user in Chicago
Chicago
Chicago is the largest city in the U.S. state of Illinois and the Midwestern United States, as well as the List of United States cities by population city in the United States with more than 2.8 million residents.... , therefore, 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
Nautical time
The establishment of nautical standard times, nautical standard time zones and the nautical date line were recommended by the Anglo-French Conference on Time-keeping at Sea in 1917.... zone letters are not used with the exception of Z.
Time zone conversions
Conversion between time zones obeys the relationship
"time in zone A" − "UTC offset for zone A" = "time in zone B" − "UTC offset for zone B",
in which each side of the equation is equivalent to UTC. (The more familiar term "UTC offset" is used here rather than the term "zone designator" used by the standard.)
The conversion equation can be rearranged to
"time in zone B" = "time in zone A" − "UTC offset for zone A" + "UTC offset for zone B".
For example, what time is it in Los Angeles (UTC offset= −08) when the New York Stock Exchange
New York Stock Exchange
New York Stock Exchange is a stock exchange based in New York City, New York. It is the largest stock exchange in the world by United States dollar market capitalization of its listed companies' Security .... opens at 09:30−05?
time in Los Angeles = 09:30 − (−05:00) + (−08:00) = 06:30
In Delhi (UTC offset= +5:30), the New York Stock Exchange opens at
time in Delhi = 09:30 − (−05:00) + (+5:30) = 20:00
These calculations become more complicated near a daylight saving boundary (because the UTC offset for zone X is a function of the UTC time).
Combined date and time representations
T
T
Combining date and time representations to represent a single point in time (time point) is quite simple. It is in the format of T
