ISO 8601 - Wikipedia

ISO 8601 - Wikipedia
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International standards for dates and times
Current date and time expressed according to ISO 8601
refresh
Date in
UTC
2026-04-24
Time in
UTC
08:08:56Z
T080856Z
Date and time
in
UTC
2026-04-24T08:08:56Z
20260424T080856Z
Date and time
with the offset
2026-04-23T20:08:56-12:00
UTC−12:00
2026-04-24T08:08:56+00:00
UTC+00:00
2026-04-24T20:08:56+12:00
UTC+12:00
Week
2026-W17
Week with weekday
2026-W17-5
Ordinal date
2026‐114
Time
Major concepts
Past
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Future
Eternity
of the world
Fields of study
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Event
Fatalism
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End time
Day of Judgement
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Afterlife
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Kalachakra
Measurement
Standards
ISO 8601
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Ultimate fate of the universe
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Spacetime
Time travel
ISO 8601
is an
international standard
covering the worldwide exchange and communication of date and
time
-related data. It is maintained by the
International Organization for Standardization
(ISO) and was first published in 1988, with updates in 1991, 2000, 2004, and 2019, and an amendment in 2022.
The standard provides a well-defined, unambiguous method of representing calendar dates and times in worldwide communications, especially to avoid misinterpreting numeric dates and times when such data is transferred between
countries with different conventions
for writing numeric dates and times.
ISO 8601 applies to these representations and formats: dates, in the
Gregorian
calendar (including the
proleptic Gregorian
calendar); times, based on the
24-hour timekeeping system
, with optional
UTC offset
time intervals
, and combinations thereof.
The standard does not assign specific meaning to any element of the dates/times represented: the meaning of any element depends on the context of its use. Dates and times represented cannot use words that do not have a specified numerical meaning within the standard (thus excluding
names of years
in the
Chinese calendar
), or that do not use
computer characters
(excludes images or sounds).
In representations that adhere to the ISO 8601 interchange standard, dates and times are arranged such that the greatest temporal term (typically a year) is placed at the left and each successively lesser term is placed to the right of the previous term. Representations must be written in a combination of
Arabic numerals
and the specific computer characters (such as "‐", ":", "T", "W", "Z") that are assigned specific meanings within the standard; that is, such commonplace descriptors of dates (or parts of dates) as "January", "Thursday", or "New Year's Day" are not allowed in interchange representations within the standard.
History
edit
The first edition of the ISO 8601 standard was published as
ISO 8601:1988
in June 1988. It unified and replaced a number of older ISO standards on various aspects of date and time notation
ISO 2014
Writing of calendar dates in all-numeric form
, published April 1976
following ISO/R 2014 from 1971, originally introduced the hyphenated,
most-to-least-significant
order notation for
Gregorian calendar
dates with day of the month as an international standard.
ISO 2015
Numbering of weeks
, also from April 1976
with ISO R 2015 from 1971, first specified the rules for determining the ordinal number of a calendar week in a year and a day within a week.
ISO 2711
Representation of ordinal dates
, issued in January 1973,
introduced the notation for the day of the year, which effectively treats only the final, 366th day of leap years differently.
ISO 3307
Representation of time of the day
, dated March 1975,
standardized 24-hour wall clock times and their notation, but without handling time zones.
ISO 4031
Representation of time of the day
, published December 1978,
added numerical offsets from UTC (or GMT back then).
This first, unified edition was superseded by a second edition,
ISO 8601:2000
, in 2000, that by a revised, third edition,
ISO 8601:2004
, published on 1 December 2004, and that by
ISO 8601-1:2019
and
ISO 8601-2:2019
on 25 February 2019. All editions and parts of ISO 8601 and its predecessors were prepared by,
10
and are under the direct responsibility of,
ISO Technical Committee
TC 154.
11
Issued in February 2019,
the fourth revision of the standard, ISO 8601-1:2019, represents slightly updated contents of the previous ISO 8601:2004 standard,
12
but is now the first of two parts. The other part, ISO 8601-2:2019, is entirely new. It defines various extensions such as uncertainties or parts of the
Extended Date/Time Format
(EDTF).
13
14
15
16
17
18
An amendment to ISO 8601-1 was published in October 2022 featuring minor technical clarifications and attempts to remove ambiguities in definitions. The most significant change, however, was the reintroduction of the "24:00:00" format to refer to the instant at the
end
of a calendar day.
An amendment to ISO 8601-2 was published in January 2025.
History of published editions and amendments
Name
Description
ISO 8601:1988
Data elements and interchange formats – Information interchange – Representation of dates and times
ISO 8601:1988/COR 1:1991
Data elements and interchange formats – Information interchange – Representation of dates and times – Technical Corrigendum 1
ISO 8601:2000
Data elements and interchange formats – Information interchange – Representation of dates and times
ISO 8601:2004
Data elements and interchange formats – Information interchange – Representation of dates and times
ISO 8601-1:2019
Date and time – Representations for information interchange – Part 1: Basic rules
ISO 8601-2:2019
Date and time – Representations for information interchange – Part 2: Extensions
ISO 8601-1:2019/Amd 1:2022
Date and time – Representations for information interchange – Part 1: Basic rules – Amendment 1: Technical corrections
ISO 8601-2:2019/Amd 1:2025
Date and time – Representations for information interchange – Part 2: Extensions – Amendment 1: Canonical expressions, extensions to time scale components and date time arithmetic
General principles
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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 or time offset. 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 – a
basic format
with a minimal number of separators or an
extended format
with separators added to enhance human readability.
19
20
The standard notes that "The basic format should be avoided in
plain text
."
21
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
"2009-01-06"
in the extended format or as "20090106" in the basic format without ambiguity.
For reduced
precision
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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.
Dates
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April 2026
Week
Mon
Tue
Wed
Thu
Fri
Sat
Sun
W14
30
31
01
02
03
04
05
W15
06
07
08
09
10
11
12
W16
13
14
15
16
17
18
19
W17
20
21
22
23
24
25
26
W18
27
28
29
30
01
02
03
The standard uses the
Gregorian calendar
, which "serves as an international standard for civil use".
23
ISO 8601 allows Gregorian dates from the introduction of the calendar on 15 October 1582. For earlier (pre-Gregorian) dates, the calendar may be extended before its introduction (the
proleptic Gregorian calendar
) by explicit agreement of the parties involved. Such proleptic dates may not be adjusted to reconcile them with Julian dates.
Years
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YYYY
ISO 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, similar to astronomical year numbering. However, years before 1583 (the first full year following the introduction of the Gregorian calendar) are not automatically allowed by the standard. Instead, the standard states that "values in the range [0000] through [1582] shall only be used by mutual agreement of the partners in information interchange".
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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.
25
An expanded year representation [±YYYYY] must have an agreed-upon number of extra year digits beyond the four-digit minimum, and it must be prefixed with a + or - sign
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instead of the more common AD/BC (or CE/BCE) notation; by convention 1 BC is labelled +0000, 2 BC is labeled -0001, and so on.
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Calendar dates
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YYYY-MM-DD
or
YYYYMMDD
YYYY-MM
but not
YYYYMM)
Only allowed in the (now superseded) 2000 version:
29
YY-MM-DD
or
YYMMDD
-YY-MM
or
-YYMM
--MM-DD
or
--MMDD
--MM
---DD
Calendar 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
"1981-04-05"
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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". One may simply write "1981" to refer to that year, "198" to refer to the
decade
from 1980 to 1989 inclusive, 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
YYYY-MM
format is allowed. By disallowing dates of the form YYYYMM, the standard avoids confusion with the
truncated representation
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YYMMDD (still often used). The 2000 version also allowed writing the truncation
"--04-05"
to mean "April 5"
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but the 2004 version does not allow omitting the year when a month is present.
Examples:
7 January 2000 can be written as "2000-01-07" or "20000107"
Week dates
edit
Main article:
ISO week date
YYYY-Www
or
YYYYWww
YYYY-Www-D
or
YYYYWwwD
Week 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
, 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 first
business day
in the starting year (considering that Saturdays, Sundays and 1 January are non-working days),
the week with the starting 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 to 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:
Monday 29 December 2008 is written "2009-W01-1"
Sunday 3 January 2010 is written "2009-W53-7"
Ordinal dates
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YYYY-DDD
or
YYYYDDD
An
ordinal date
is an
ordinal
format for the multiples of a day elapsed since the start of year.
It is represented as "YYYY-DDD" (or YYYYDDD), where [YYYY] indicates a year and [DDD] is the "day of year", from 001 through 365 (366 in
leap years
). For example,
"1981-04-05"
is the same as
"1981-095"
This simple form is preferable 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.
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
1 January 4713 BC
Greenwich noon, Julian proleptic calendar (or noon on ISO date
-4713-11-24
which uses the Gregorian proleptic calendar with a year 0000).
Times
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Thh:mm:ss.sss
or
Thhmmss.sss
Thh:mm:ss
or
Thhmmss
Thh:mm.mmm
or
Thhmm.mmm
Thh:mm
or
Thhmm
Thh.hhh
Thh
In unambiguous contexts
hh:mm:ss.sss
or
hhmmss.sss
hh:mm:ss
or
hhmmss
hh:mm
or
hhmm
hh
ISO 8601 uses the
24-hour clock
system. As of ISO 8601-1:2019, the
basic format
is T[hh][mm][ss] and the
extended format
is T[hh]:[mm]:[ss]. Earlier versions omitted the T (representing time) in both formats.
[hh] refers to a zero-padded
hour
between 00 and 24.
[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 "T134730" in the
basic format
or "T13:47:30" in the
extended format
. ISO 8601-1:2019 allows the T to be omitted in the extended format, as in "13:47:30", but only allows the T to be omitted in the basic format when there is no risk of confusion with date expressions.
Either the seconds, or the minutes and seconds, may be omitted from the basic or extended time formats for greater brevity but decreased precision; the resulting reduced precision time formats are:
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T[hh][mm] in
basic format
or T[hh]:[mm] in
extended format
, when seconds are omitted.
T[hh], when both seconds and minutes are omitted.
As of ISO 8601-1:2019/Amd 1:2022, "00:00:00" may be used to refer to
midnight
corresponding to the instant at the beginning of a calendar day; and "24:00:00" to refer to midnight corresponding to the instant at the end of a calendar day.
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ISO 8601-1:2019 as originally published removed "24:00:00" as a representation for the end of day although it had been permitted in earlier versions of the standard.
A decimal fraction may be added to the lowest order time element present in any of these representations. A
decimal mark
, either a
comma
or a
dot on the baseline
, is used as a separator between the time element and its fraction. (Following
ISO 80000-1
according to ISO 8601:1-2019,
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it does not stipulate a preference except within International Standards, but with a preference for a
comma
according to ISO 8601:2004.
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For example, to denote "14 hours, 30 and one half minutes", do not include a seconds figure; represent it as "14:30,5", "T1430,5", "14:30.5", or "T1430.5".
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 for a DATETIME, i.e., "yyyy-mm-ddThh:mm:ss[.mmm]".
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Time zone designators
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Z
±hh:mm
±hhmm
±hh
Time zones
in ISO 8601 are represented as local time (with the location unspecified), as
UTC
, or as an offset from UTC.
Local time (unqualified)
edit
If no UTC relation 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. Even within a single geographic time zone, some local times will be ambiguous if the region observes
daylight saving time
. It is usually preferable to indicate a time zone (zone designator) using the standard's notation.
Coordinated Universal Time (UTC)
edit
If the time is in
UTC
, add a
directly after the time without a space.
is the zone designator for the zero UTC offset. "09:30 UTC" is therefore represented as "09:30Z" or "T0930Z". "14:45:15 UTC" would be "14:45:15Z" or "T144515Z".
The
suffix in the ISO 8601 time representation is sometimes referred to as "Zulu time" or "Zulu meridian" because the same letter is used to designate the
Zulu time zone
35
However, the ACP 121 standard that defines the list of military time zones makes no mention of UTC and derives the "Zulu time" from the
Greenwich Mean Time
36
which was formerly used as the international civil time standard.
GMT
is no longer precisely defined by the scientific community and can refer to either UTC or
UT1
depending on context.
37
Time offsets from UTC
edit
The
UTC offset
is appended directly to the time instead of "Z" suffix above; other
nautical time
zone letters are not used. The offset is applied to
UTC
to get the
civil time
in the designated
time zone
in the format '±[hh]:[mm]', '±[hh][mm]', or '±[hh]'.
A negative
UTC offset
describes a time zone west of the
prime meridian
where the civil time is behind UTC. So the zone designation for
New York
(on
standard time
) would be "−05:00","−0500", or "−05".
Conversely, a positive UTC offset describes a time zone east of the prime meridian where the civil time is ahead of
UTC
. So the zone designation for
Cairo
will be "+02:00","+0200", or "+02".
A time zone where the civil time coincides with UTC is always designated as positive, though the offset is zero (see related specifications below). So the zone designation for
London
(on
standard time
) would be "
+00:00
", "
+0000
", or "
+00
".
Additional examples
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−10:00
" for
Honolulu
−06:00
" for
Chicago
on
standard time
, or
Denver
on
daylight saving time
−03:00
" for
Brasília
+01:00
" for
London
on
British Summer Time
+04:00
" for
Dubai
+05:30
" for
India
+09:00
" for
Japan
See
List of UTC offsets
for other
UTC offsets
Other time offset specifications
edit
It is not permitted to state a zero value time offset with a negative sign, as "−00:00", "−0000", or "−00". The section dictating sign usage states that a plus sign must be used for a positive or zero value, and a minus sign for a negative value. A
plus-minus-sign (
may also be used if it is available.
38
Contrary to this rule, RFC 3339, which is otherwise a profile of ISO 8601, permits the use of "−00" with the same denotation as "+00" but a differing connotation: an unknown
UTC offset
39
40
To represent a negative offset, ISO 8601 specifies using a
minus sign
). If the interchange character set is limited and does not have a minus sign character, then the
hyphen-minus
should be used (
).
41
ASCII
does not have a minus sign, so its hyphen-minus character (code 45
10
) would be used. If the character set has a minus sign, such as
U+2212
MINUS SIGN
in
Unicode
, then that character should be used. The
HTML character entity
invocation for
is
−
ISO 8601-2:2019 allows for general durations for time offsets. For example, more precision can be added to the time offset with the format '±[hh]:[mm]:[ss].[sss]' or '±[n]H[n]M[n]S' as below.
Combined date and time representations
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T
A single point in time can be represented by concatenating a complete date expression, the letter
"T"
as a delimiter, and a valid time expression. For example,
"2007-04-05T14:30"
. In ISO 8601:2004 it was permitted to omit the
"T"
character by mutual agreement as in
"200704051430"
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but this provision was removed in ISO 8601-1:2019.
Separating date and time parts with other characters such as space is not allowed in ISO 8601, but allowed in its profile RFC 3339.
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If a time zone designator is required, it follows the combined date and time. For example,
"2007-04-05T14:30Z"
or
"2007-04-05T12:30-02:00"
Either basic or extended formats may be used, but both date and time must use the same format. The date expression may be calendar, week, or ordinal, and must use a complete representation. The time may be represented using a specified reduced precision format.
Durations
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PnYnMnDTnHnMnS
PnW
PT
Durations define the amount of intervening time in a time interval and are represented by the format P[n]Y[n]M[n]DT[n]H[n]M[n]S or P[n]W as shown on the aside. In these representations, the [n] is replaced by the value for each of the date and time elements that follow the [n]. Leading zeros are not required, but the maximum number of digits for each element should be agreed to by the communicating parties. The capital letters
, and
are designators for each of the date and time elements and are not replaced.
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is the duration designator (for
period
) placed at the start of the duration representation.
is the year designator that follows the value for the number of calendar years.
is the month designator that follows the value for the number of calendar months.
is the week designator that follows the value for the number of weeks.
is the day designator that follows the value for the number of calendar days.
is the time designator that precedes the time components of the duration representation.
is the hour designator that follows the value for the number of hours.
is the minute designator that follows the value for the number of minutes.
is the second designator that follows the value for the number of seconds.
For example, "P3Y6M4DT12H30M5S" represents a duration of "three years, six months, four days, twelve hours, thirty minutes, and five seconds".
Date and time elements including their designator may be omitted if their value is zero, and lower-order elements may also be omitted for reduced precision. For example, "P23DT23H" and "P4Y" are both acceptable duration representations. However, at least one element must be present, thus "P" is not a valid representation for a duration of 0 seconds. "PT0S" or "P0D", however, are both valid and represent the same duration.
To resolve ambiguity, "P1M" is a one-month duration and "PT1M" is a one-minute duration (note the time designator, T, that precedes the time value). The smallest value used may also have a decimal fraction,
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as in "P0.5Y" to indicate half a year. This decimal fraction may be specified with either a
comma
or a
full stop
, as in "P0,5Y" or "P0.5Y". The standard does not prohibit date and time values in a duration representation from exceeding their "carry over points" except as noted below. Thus, "PT36H" could be used as well as "P1DT12H" for representing the same duration. But keep in mind that "PT36H" is not the same as "P1DT12H" when switching to or from
daylight saving time
Alternatively, a format for duration based on combined date and time representations may be used by agreement between the communicating parties either in the basic format PYYYYMMDDThhmmss or in the extended format
P[YYYY]-[MM]-[DD]T[hh]:[mm]:[ss]
. For example, the first duration shown above would be
"P0003-06-04T12:30:05"
. However, individual date and time values cannot exceed their
moduli
(e.g. a value of 13 for the month or 25 for the hour would not be permissible).
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The standard describes a duration as part of time intervals, which are discussed in the next section. The duration format on its own is ambiguous regarding the total number of days in a calendar year and calendar month. The number of seconds in a calendar day is also ambiguous because of
leap seconds
. For example "P1M" on its own could be 28, 29, 30, or 31 days. There is no ambiguity when used in a time interval. Using example "P2M" duration of two calendar months:
interval 2003-02-15T00:00:00Z/P2M ends two calendar months later at 2003-04-15T00:00:00Z which is 59 days later
interval 2003-07-15T00:00:00Z/P2M ends two calendar months later at 2003-09-15T00:00:00Z which is 62 days later
The duration format (or a subset thereof) is widely used independent of time intervals, as with the Java 8 Duration class which supports a subset of the duration format.
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Time intervals
edit
/
/
/

A time interval is the intervening time between two time points. The amount of intervening time is expressed by a duration (as described in the previous section). The two time points (start and end) are expressed by either a combined date and time representation or just a date representation.
There are four ways to express a time interval:
Start and end, such as "2007-03-01T13:00:00Z/2008-05-11T15:30:00Z"
Start and duration, such as "2007-03-01T13:00:00Z/P1Y2M10DT2H30M"
Duration and end, such as "P1Y2M10DT2H30M/2008-05-11T15:30:00Z"
Duration only, such as "P1Y2M10DT2H30M", with additional context information
Of these, the first three require two values separated by an
interval designator
which is usually a solidus (more commonly referred to as a
forward slash
"/"). Section 3.2.6 of ISO 8601-1:2019 notes that "A solidus may be replaced by a double hyphen ["--"] by mutual agreement of the communicating partners", and previous versions used notations like "2000--2002".
49
Use of a double hyphen instead of a solidus allows inclusion in computer
filenames
50
in common operating systems, a solidus is a
reserved character
and is not allowed in a filename.
For / expressions, if any elements are missing from the end value, they are assumed to be the same as for the start value including the time zone. This feature of the standard allows for concise representations of time intervals. For example, the date of a two-hour meeting including the start and finish times could be shown as "2007-12-14T13:30/15:30", where "/15:30" implies "/2007-12-14T15:30" (the same date as the start), or the beginning and end dates of a monthly billing period as "2008-02-15/03-14", where "/03-14" implies "/2008-03-14" (the same year as the start).
If greater precision is desirable to represent the time interval, then more time elements can be added to the representation. An interval denoted
"2007-11-13/15"
can start at any time on
2007-11-13
and end at any time on
2007-11-15
, whereas
"2007-11-13T09:00/15T17:00"
includes the start and end times.
To explicitly include all of the start and end dates, the interval would be represented as
"2007-11-13T00:00/16T00:00"
Recurring intervals
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Rn/
R/
Repeating intervals are specified in clause "4.5 Recurring time interval". They are formed by adding "R[n]/" to the beginning of an interval expression, where
is used as the letter itself and [n] is replaced by the number of repetitions. Leaving out the value for [n] or specifying a value of -1, means an unbounded number of repetitions. A value of 0 for [n] means the interval is not repeated.
If the interval specifies the start (forms 1 and 2 above), then this is the start of the repeating interval. If the interval specifies the end but not the start (form 3 above), then this is the end of the repeating interval. For example, to repeat the interval of "P1Y2M10DT2H30M" five times starting at
"2008-03-01T13:00:00Z"
, use
"R5/2008-03-01T13:00:00Z/P1Y2M10DT2H30M"
It is based on syntax from
iCalendar
and shared by IETF RFC 5545.
51
Truncated representations (deprecated)
edit
Not to be confused with
§ Reduced precision
ISO 8601:2000 allowed truncation (by agreement), where leading components of a date or time are omitted. Notably, this allowed two-digit years to be used as well as the ambiguous formats YY-MM-DD and YYMMDD. This provision was removed in ISO 8601:2004.
Some truncated representations (last valid in ISO 8601:2000)
Type
Basic format
Basic example
Extended format
Extended example
A specific date in the implied century
YYMMDD
851026
YY-MM-DD
85-10-26
A specific year and month in the implied century
-YYMM
-8510
-YY-MM
-85-10
A specific year in the implied century
-YY
-85
N/a
A specific day of a month in the implied year
--MMDD
--1026
--MM-DD
--10-26
A specific month in the implied year
--MM
--10
N/a
A specific day in the implied month
---DD
---26
A specific year and ordinal day in the implied century
YYDDD
85299
YY-DDD
85-299
A specific ordinal day in the implied year
-DDD
-299
N/a
A specific year and week in the implied decade
-YWww
-5W43
-Y-Www
-5-W43
A specific week and day in the implied year
-WwwD
-W436
-Www-D
-W43-6
A specific day in the implied week
-W-D
-W-6
N/a
A specific minute and second of the implied hour
-mmss
-3456
-mm:ss
-34:56
A specific second of the implied minute
-ss
-56
N/a
A specific minute and decimal fraction of the implied hour
-mm,m
-34,9
N/a
The first and seventh examples given above omit the leading
for century. Other formats have one leading
per omitted century, year, month, week, hour and minute as necessary to disambiguate the format.
Standardised extensions
edit
ISO 8601-2:2019 defines a set of standardised extensions to the ISO 8601 date and time formats.
Extended Date/Time Format (EDTF)
edit
The EDTF is given as an example of a profile of ISO 8601 in Part 2. It comes in three levels, where level 0 is a subset of Part 1 restricted to extended month–day notation, CCYY-MM-DD, similar to RFC 3339, and levels 1 and 2 build upon that.
EDTF is mostly tailored to bibliographic and historiographic needs. Some of its features are:
13
Uncertain
and approximate qualifiers, '?' and '~', as well as their combined use, '%'; they can be applied to the whole date or to individual components.
Time intervals with an open (unbounded) or unknown end or start, e.g. "../2025" or "2024/".
Exponential ('E') and significant figure ('S') notation in years with a new 'Y' prefix, e.g. "Y-1.25E6S2".
Special "month" values indicating sub-year groupings such as seasons and quarters, e.g. "2025-26" for summer in the Northern hemisphere.
Syntax for serializing a list of dates within brackets '[]' for single choices or braces '{}' for inclusive lists.
The EDTF features are described in the "Date and Time Extensions" section of ISO 8601-2:2019, and the profile itself is found as Annex A. It is virtually identical to the prior specification pioneered by the US Library of Congress.
13
Implementations
edit
GNU CoreUtils
's date command has an
--iso-8601
option
52
among other formating patterns:
date
--iso-8601
ns
2025-02-16T12:03:17,646296349+01:00
date
-u
--rfc-3339
ns
2025-02-16 10:58:44.966864492+00:00
date
-u
"%Y-%m-%dT%H:%M:%S.%6NZ"
2025-02-16T10:58:44.965071Z
Usage
edit
On the
Internet
, the
World Wide Web Consortium
(W3C) uses the
IETF
standard based on 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. The very simple specification is based on a draft of the RFC 3339 mentioned below.
53
ISO 8601 is referenced by several specifications, but the full range of options of ISO 8601 is not always used. For example, the various
electronic program guide
standards for TV, digital radio, etc. use several forms to describe points in time and durations. The
ID3
audio meta-data specification also makes use of a subset of ISO 8601.
54
The
X.690
encoding standard's
GeneralizedTime
makes use of another subset of ISO 8601.
Commerce
edit
As of 2006, the
ISO week date
appears in its basic form on major brand commercial packaging in the United States.
citation needed
Its appearance depended on the particular packaging, canning, or bottling plant more than any particular brand. The format is particularly useful for quality assurance, so that production errors can be readily traced.
RFCs
edit
IETF RFC 3339
55
defines a profile of ISO 8601 for use in
Internet protocols
and
standards
. It explicitly excludes durations and dates before the
common era
. The more complex formats such as week numbers and ordinal days are not permitted.
56
RFC 3339 deviates from ISO 8601 in allowing a zero time zone offset to be specified as "-00:00", which ISO 8601 forbids. RFC 3339 intends "-00:00" to carry the connotation that it is not stating a preferred time zone, whereas the conforming "+00:00" or any non-zero offset connotes that the offset being used is preferred. This convention regarding "-00:00" is derived from earlier RFCs, such as RFC 2822 which uses it for timestamps in
email
headers.
57
RFC 2822 made no claim that any part of its timestamp format conforms to ISO 8601, and so was free to use this convention without conflict.
Building upon the foundations of RFC 3339, the
IETF
introduced the Internet Extended Date/Time Format (IXDTF) in RFC 9557.
58
This format extends the timestamp representation to include additional information such as an associated time zone name. The inclusion of time zone names is particularly useful for applications that need to account for events like daylight saving time transitions. Furthermore, IXDTF maintains compatibility with pre-existing syntax for attaching time zone names to timestamps, providing a standardized and flexible approach to timestamp representation on the internet. Example:
1996-12-19T16:39:57-08:00[America/Los_Angeles]
Adoption as national standards
edit
Australia
AS/NZS ISO 8601.1:2021, AS/NZS ISO 8601.2:2021 (replaced AS ISO 8601-2007)
Austria
ÖNORM ISO 8601 (replaced ÖNORM EN 28601)
Belgium
NBN EN 28601 (1993)
Brazil
NBR 5892:2019
Canada
ISO 8601-1:2019/Amd 1:2022
59
Colombia
NTC 1034:2014
60
China
GB/T 7408-2005
Czech Republic
ČSN ISO 8601 (replaced ČSN EN 28601) (Obsolete as of 2019. No standard was given in exchange.
61
Denmark
DS/ISO 8601:2005 (replaced DS/EN 28601)
Estonia
EVS 8:2008; EVS-ISO 8601:2011
European Norm
EN ISO 8601, EN 28601:1992 (cancelled 7 October 2011)
Finland
SFS-EN 28601
France
NF Z69-200; NF EN 28601:1993-06-01 (cancelled)
Germany
DIN ISO 8601:2006-09 (replaced DIN EN 28601:1993-02); related: DIN 5008:2011-04 (replaced DIN 5008:2005-05, DIN 5008:2001-11, DIN 5008:1996-05)
Greece
ELOT EN 28601
Hungary
MSZ ISO 8601:2003
Iceland
IST EN 28601:1992 (obsolete)
India
IS 7900:2001
Ireland
IS/EN 28601:1993
Italy
UNI EN 28601 (1993)
Japan
JIS X 0301:2002
Korea, Republic of
KS X ISO 8601
Lithuania
LST ISO 8601:2006 (replaced LST ISO 8601:1997)
Luxembourg
ITM-EN 28601
Mexico
NMX-CH-150-IMNC-1999
62
Netherlands
NEN ISO 8601, NEN EN 28601 (1994), NEN 2772
New Zealand
AS/NZS ISO 8601.1:2021, AS/NZS ISO 8601.2:2021
Norway
NS-ISO 8601
Poland
PN-EN 28601:2002 (Obsolete as of 2008. No standard was given in exchange.
63
Portugal
NP EN 28601
Russia
ГОСТ ИСО 8601-2001 (current), ГОСТ 7.64-90 (obsolete)
South Africa
SANS 8601:2009
64
Spain
UNE EN 28601:1995
Sweden
SS-ISO 8601-1:2022,
65
contains the official English version of ISO 8601-1:2019. (Approved 2022-05-13, replaces SS-ISO 8601:2011, edition 2)
Switzerland
SN ISO 8601:2005-08 (replaced SN-EN 28601:1994)
Taiwan
CNS 7648
Thailand
TIS 1111:2535 (1992)
Turkey
TS ISO 8601-1
66
and TS ISO 8601-2
67
(Accepted from 2021-02-15)
Ukraine
ДСТУ ISO 8601:2010
United Kingdom
BS ISO 8601:2004, BS EN 28601 (1989-06-30)
United States
ANSI INCITS 30-1997 (R2008) and NIST FIPS PUB 4-2
Vietnam
TCVN 6398-1:1998
68
See also
edit
Astronomical year numbering
Date and time representation by country
List of date formats by country
Chronometry
Notes and references
edit
"German 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).
Archived
from the original on 2017-10-20
. Retrieved
2017-10-19
ISO 8601:2004[E] section 1 Scope
"Introduction to the new ISO 8601-1 and ISO 8601-2"
ISO/TC 154
. 26 August 2019.
ISO 8601:2004(E)
ISO
, 2004-12-01,
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.
ISO/TC 154.
"ISO 2014:1976 - Writing of calendar dates in all-numeric form"
{{
cite web
}}
: CS1 maint: numeric names: authors list (
link
ISO/TC 154.
"ISO 2015:1976 - Numbering of weeks"
{{
cite web
}}
: CS1 maint: numeric names: authors list (
link
ISO/TC 154.
"ISO 2711:1973 - Information processing interchange — Representation of ordinal dates"
{{
cite web
}}
: CS1 maint: numeric names: authors list (
link
ISO/TC 154.
"ISO 3307:1975 - Information interchange — Representation of time of the day"
{{
cite web
}}
: CS1 maint: numeric names: authors list (
link
ISO/TC 154.
"ISO 4031:1978 - Information interchange — Representation of local time differentials"
{{
cite web
}}
: CS1 maint: numeric names: authors list (
link
ISO 8601:2004(E)
ISO
. 2004-12-01. p. iv Foreword.
"TC 154 Processes, data elements and documents in commerce, industry and administration"
. Technical committees. ISO.
Archived
from the original on 2016-05-25
. Retrieved
2014-08-16
"ISO/DIS 8601-1:2016-10-26"
(PDF)
Library of Congress
. Archived from
the original
(PDF)
on 2017-10-19.
"Extended Date/Time Format (EDTF) Specification"
The Library of Congress
. 2019-10-08 [2019-02-04, 2014, 2012].
Archived
from the original on 2020-03-07
. Retrieved
2020-03-07
"Extended Date/Time Format (EDTF) Background"
The Library of Congress
. 2019-10-08 [2019-03-01].
Archived
from the original on 2020-03-07
. Retrieved
2020-03-07
"Extended Date/Time Format (EDTF) 1.0 2012/2014"
. Draft Submission.
The Library of Congress
. Archived from
the original
on 2017-07-15
. Retrieved
2017-07-15
"ISO/WD 8601-2:2016-02-16"
(PDF)
Library of Congress
. Archived from
the original
(PDF)
on 2017-10-19.
"ISO/DIS 8601-2:2016-10-26"
(PDF)
Library of Congress
. Archived from
the original
(PDF)
on 2017-10-20.
"German 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).
Archived
from the original on 2017-10-19
. Retrieved
2017-10-19
ISO: "
ISO 8601 — Date and time format
".
Archived
2013-03-08 at the
Wayback Machine
Wolf, Misha; Wicksteed, Charles (15 September 1997).
"Date and Time Formats"
W3C
Archived
from the original on 10 May 2021
. Retrieved
11 May
2021
ISO 8601:2004 section 2.3.3 basic format
Earlier versions of ISO 8601 used the word
accuracy
, not
precision
, in the relevant section, e.g: 2.3.7 representation with reduced accuracy. This was corrected in ISO 8601-1:2019.
Doggett, L. E. (1992). "Calendars". In P. K. Seidelmann (ed.).
Explanatory Supplement to the Astronomical Almanac
. Sausalito, California: University Science Books. p. 580.
ISBN
0-935702-68-7
. Archived from
the original
on 2004-04-01.
The Gregorian calendar today serves as an international standard for civil use.
ISO 8601:2004(E)
ISO
. 2004-12-01. section 4.1.2.1 General.
ISO 8601:2004(E)
ISO
. 2004-12-01.
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 8601:2004 sections 3.4.2, 4.1.2.4
For example, see Annex B.1.1 of the standard.
Perreault, S. (August 2011).
"DATE"
vCard Format Specification
IETF
. sec. 4.3.1.
doi
10.17487/RFC6350
RFC
6350
. Retrieved
2021-01-21
Truncated representation, as specified in [ISO.8601.2000], Sections 5.2.1.3 d), e), and f), is permitted.
Last in ISO 8601:2000, removed in ISO 8601:2004, in use by RFC6350
28
ISO 8601-1:2019/Amd 1:2022
ISO
, 2022-10-25
ISO 8601-1:2019 section 5.3.1.3 Representations with reduced precision
ISO 8601-1:2019 section 3.1.3.9 Decimal sign
ISO 8601:2004(E)
ISO
, 2004-12-01,
4.2.2.4 ... 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.
"ISO 8601 Format"
TechNet
Microsoft Docs
. 3 December 2008.
Archived
from the original on 2021-10-20
. Retrieved
2021-10-20
Markus Kuhn (2020-06-16).
"A summary of the international standard date and time notation"
Archived
from the original on 2022-10-05
. Retrieved
2022-10-05
"Communication Instructions General ACP 121(I)"
(PDF)
Combined Communications Electronics Board
. October 2010.
Archived
(PDF)
from the original on 2018-01-16
. Retrieved
2018-01-15
McCarthy, Dennis D.
; Seidelmann, Kenneth P. (2009).
Time: From Earth Rotation to Atomic Physics
. Weinheim:
Wiley-VCH Verlag GmbH & Co. KGaA
. p. 10.
ISBN
978-3-527-40780-4
ISO 8601-1:2019 section 3.2.4, ISO 8601:2004 section 3.4.2
RFC 3339 – Unknown local offset convention
Newman, Chris (July 2002).
"Unknown Local Offset Convention"
. In Klyne, Graham (ed.).
Date and Time on the Internet:Timestamps
IETF
. sec. 4.3.
doi
10.17487/RFC3339
RFC
3339
. Retrieved
1 February
2021
If the time in UTC is known, but the offset to local time is unknown, this can be represented with an offset of "-00:00". This differs semantically from an offset of "Z" or "+00:00", which imply that UTC is the preferred reference point for the specified time. RFC2822 [IMAIL-UPDATE] describes a similar convention for email
"3.4.1 Characters used in the representations - Introduction".
Data elements and interchange formats — Information interchange - Representation of dates and times — Part 1: Basic rules
(PDF)
ISO
. 2016-02-16. p. 12. ISO/WD 8601-1.
In an environment where use is made of a character repertoire based on ISO/IEC 646, "hyphen" and "minus" are both mapped onto "hyphen-minus". Representations with a "plus-minus" shall only be used in such environment if the interchange repertoire includes "plus-minus"
{{
citation
}}
: CS1 maint: deprecated archival service (
link
ISO 8601:2004(E): Data elements and interchange formats — Information interchange — Representation of dates and times
ISO
. 2004-12-01.
4.3.2 NOTE: By mutual agreement of the partners in information interchange, the character [T] may be omitted in applications where there is no risk of confusing a date and time of day representation with others defined in this International Standard.
G. Klyne; C. Newman (July 2002).
"Internet Date/Time Format"
Date and Time on the Internet: Timestamps
IETF
. sec. 5.6.
doi
10.17487/RFC3339
RFC
3339
NOTE: ISO 8601 defines date and time separated by "T". Applications using this syntax may choose, for the sake of readability, to specify a full-date and full-time separated by (say) a space character.
"Data elements and interchange formats — Information interchange - Representation of dates and times — Part 1: Basic rules"
(PDF)
Library of Congress
. p. 23.
Archived
(PDF)
from the original on 2021-03-12
. Retrieved
2025-10-11
§ 4.4.3.2 Format with designators. [...] the maximum number of digits in a component needs to be agreed by the partners in information interchange. [...]
"Data elements and interchange formats — Information interchange - Representation of dates and times — Part 1: Basic rules"
(PDF)
The Library of Congress
. p. 23.
Archived
(PDF)
from the original on 2021-03-12
. Retrieved
2021-07-06
b) If necessary for a particular application, the lowest order components may have a decimal fraction.
ISO 8601:2004 section 4.4.3.3 Alternative format, ISO 8601-1:2019 section 5.5.2.4 Alternative format
"Java 8 Class Duration"
Java Platform Standard Edition 8
. Oracle.
Archived
from the original on 2017-10-14
. Retrieved
2017-10-07
"Amazon Alexa Duration"
Amazon Developer
. Amazon.com.
Archived
from the original on 2017-10-14
. Retrieved
2017-10-07
"Info on ISO 8601, the date and time representation standard"
. Cs.tut.fi.
Archived
from the original on 2017-10-14
. Retrieved
2012-08-29
"ISO 8601 - Getting with the Times (and Dates)"
. Hydrogold. 2012-01-01.
Archived
from the original on 2014-01-25
. Retrieved
2013-08-13
RFC 5545
IETF
doi
10.17487/RFC5545
Options for date
Note about Date and Time Formats to W3C from Reuters
Archived
2011-08-24 at the
Wayback Machine
Nilsson, M. (2000-11-01).
"ID3 tag version 2.4.0 - Main Structure"
. id3.org. pp. §4. Archived from
the original
on 2015-03-09
. Retrieved
2009-09-27
Newman, Chris; Klyne, Graham (July 2002).
Date and Time on the Internet: Timestamps
IETF
doi
10.17487/RFC3339
RFC
3339
. Retrieved
2015-10-25
Newman, Chris; Klyne, Graham (July 2002).
"Internet Date/Time Format"
Date and Time on the Internet: Timestamps
IETF
. p. 8. sec. 5.6.
doi
10.17487/RFC3339
RFC
3339
. Retrieved
2015-10-25
"Date and Time Specification"
Internet Message Format
IETF
. April 2001. p. 14. sec. 3.3.
doi
10.17487/RFC2822
RFC
2822
Sharma, Ujjwal; Bormann, Carsten (2024).
Date and Time on the Internet: Timestamps with Additional Information
IETF
doi
10.17487/RFC9557
RFC
9557
. Retrieved
2024-05-28
National Standard of Canada,
"ISO 8601-1:2019/Amd 1:2022: Date and time — Representations for information interchange"
Standards Council of Canada
. 2022-10-24
. Retrieved
2025-03-22
Source ICONTEC (This standard is identical to ISO 8601:2004)
Archived
2020-01-16 at the
Wayback Machine
"ČSN ISO 8601 (979738) Datové prvky a formáty výměny - Výměna informací - Zobrazení data a času"
. 2023-04-17
. Retrieved
2023-04-17
"DOF - Diario Oficial de la Federación"
Archived
from the original on 2021-11-10
. Retrieved
2021-11-10
Czubla, Albin (2020-12-04).
"Główny Urząd Miar"
(PDF)
Główny Urząd Miar
. Retrieved
2020-12-04
"SANS 8601:2009 (Ed. 2.00)"
SABS Webstore
Archived
from the original on 2021-11-24
. Retrieved
2021-11-24
"SS-ISO 8601-1:2022"
SIS Webstore
. Retrieved
2023-10-06
TS ISO 8601-1
TS ISO 8601-2
TCVN 6398-1:1998
External links
edit
Wikimedia Commons has media related to
ISO 8601
ISO's catalog entry for ISO 8601-2:2019
Use international date format (ISO) – Quality Web Tips
by the World Wide Web Consortium (W3C)
ISO 8601 summary
by Dr. Markus Kuhn from
Cambridge University
Summary of 8601 by ISO
at the
Wayback Machine
(archived 2011-06-14)
The Mathematics of the ISO 8601 Calendar
from the website of R.H. van Gent of
Utrecht University
RFC 3339 vs ISO 8601
Venn diagram
illustrating the difference between the two standards
ISO 8601 and computing differences between dates
on
Wikiversity
Time measurement
and
standards
International standards
Coordinated Universal Time
offset
UT
ΔT
DUT1
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1–9999
16
17
31
-0
-1
-3
-4
-5
-6
-7
-8
-9
-10
-11
-12
-13
68-1
128
216
217
226
228
233
259
261
262
302
306
361
500
518
519
639
-1
-2
-3
-5
-6
646
657
668
690
704
732
764
838
843
860
898
965
999
1000
1004
1007
1073-1
1073-2
1155
1413
1538
1629
1745
1989
2014
2015
2022
2033
2047
2108
2145
2146
2240
2281
2533
2709
2711
2720
2788
2848
2852
2921
3029
3103
3166
-1
-2
-3
3297
3307
3601
3602
3864
3901
3950
3977
4031
4157
4165
4217
4909
5218
5426
5427
5428
5725
5775
5776
5800
5807
5964
6166
6344
6346
6373
6385
6425
6429
6438
6523
6709
6943
7001
7002
7010
7027
7064
7098
7185
7200
7498
-1
7637
7736
7810
7811
7812
7813
7816
7942
8000
8093
8178
8217
8373
8501-1
8571
8583
8601
8613
8632
8651
8652
8691
8805/8806
8807
8820-5
8859
-1
-2
-3
-4
-5
-6
-7
-8
-8-I
-9
-10
-11
-12
-13
-14
-15
-16
8879
9000/9001
9036
9075
9126
9141
9227
9241
9293
9314
9362
9407
9496
9506
9529
9564
9592/9593
9594
9660
9797-1
9897
9899
9945
9984
9985
9995
10000–19999
10006
10007
10116
10118-3
10160
10161
10165
10179
10206
10218
10279
10303
-11
-21
-22
-28
-238
10383
10585
10589
10628
10646
10664
10746
10861
10957
10962
10967
11073
11170
11172
11179
11404
11544
11783
11784
11785
11801
11889
11898
11940
-2
11941
11941 (TR)
11992
12006
12052
12182
12207
12234-2
12620
13211
-1
-2
13216
13250
13399
13406-2
13450
13485
13490
13567
13568
13584
13616
13816
13818
14000
14031
14224
14289
14396
14443
14496
-2
-3
-6
-10
-11
-12
-14
-17
-20
14617
14644
14649
14651
14698
14764
14882
14971
15022
15118
15189
15288
15291
15398
15408
15444
-3
-9
15445
15438
15504
15511
15686
15693
15706
-2
15707
15897
15919
15924
15926
15926 WIP
15930
15938
16023
16262
16355-1
16485
16612-2
16750
16949 (TS)
17024
17025
17100
17203
17369
17442
17506
17799
18004
18014
18181
18245
18629
18760
18916
19005
19011
19092
-1
-2
19114
19115
19125
19136
19407
19439
19500
19501
19502
19503
19505
19506
19507
19508
19509
19510
19600
19650
19752
19757
19770
19775-1
19794-5
19831
20000–29999
20000
20022
20121
20400
20802
20830
21000
21001
21047
21122
21500
21778
21827
22000
22275
22300
22301
22395
22537
23000
23003
23008
23009
23090-3
23092
23094-1
23094-2
23270
23271
23360
23941
24517
24613
24617
24707
24728
25178
25964
26000
26262
26300
26324
27000 series
27000
27001
27002
27005
27006
27729
28000
29110
29148
29199-2
29500
30000+
30170
31000
32000
37001
38500
39075
40230
40240
40250
40260
40314
40500
42010
45001
50001
55000
56000
80000
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