ISO 8601:2004

Data elements and interchange formats - Information interchange - Representation of dates and times

ISO 8601:2004 is applicable whenever representation of dates in the Gregorian calendar, times in the 24-hour timekeeping system, time intervals and recurring time intervals or of the formats of these representations are included in information interchange. It includes calendar dates expressed in terms of calendar year, calendar month and calendar day of the month; ordinal dates expressed in terms of calendar year and calendar day of the year; week dates expressed in terms of calendar year, calendar week number and calendar day of the week; local time based upon the 24-hour timekeeping system; Coordinated Universal Time of day; local time and the difference from Coordinated Universal Time; combination of date and time of day; time intervals; recurring time intervals. ISO 8601:2004 does not cover dates and times where words are used in the representation and dates and times where characters are not used in the representation. ISO 8601:2004 does not assign any particular meaning or interpretation to any data element that uses representations in accordance with ISO 8601:2004. Such meaning will be determined by the context of the application.

Éléments de données et formats d'échange — Échange d'information — Représentation de la date et de l'heure

General Information

• Status: Withdrawn
• Publication Date: 02-Dec-2004
• Withdrawal Date: 02-Dec-2004
• ICS: 01.140.30 - Documents in administration, commerce and industry
• Technical Committee: ISO/TC 154 - Processes, data elements and documents in commerce, industry and administration
• Drafting Committee: ISO/TC 154 - Processes, data elements and documents in commerce, industry and administration
• Current Stage: 9599 - Withdrawal of International Standard
• Start Date: 25-Feb-2019
• Completion Date: 13-Dec-2025
• Directive: TP162 - Zakon o ratifikaciji Konvencije o začasnem uvozu (MKZU)

Relations

• Revised: ISO 8601-1:2019 - Date and time - Representations for information interchange - Part 1: Basic rules
• Effective Date: 05-Mar-2016
• Revised: ISO 8601-2:2019 - Date and time - Representations for information interchange - Part 2: Extensions
• Effective Date: 05-Mar-2016
• Revises: ISO 8601:2000 - Data elements and interchange formats - Information interchange - Representation of dates and times
• Effective Date: 15-Apr-2008

Standards Content (Sample)

INTERNATIONAL ISO
STANDARD 8601
Third edition
2004-12-01
Data elements and interchange
formats — Information interchange —
Representation of dates and times
Éléments de données et formats d'échange — Échange
d'information — Représentation de la date et de l'heure

Reference number
©
ISO 2004
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©  ISO 2004
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ii © ISO 2004 – All rights reserved

Contents Page
Foreword. iv
Introduction . v
1 Scope. 1
2 Terms and definitions. 1
2.1 Basic concepts. 1
2.2 Time units, nominal durations and time intervals . 4
2.3 Representations and formats . 7
3 Fundamental principles. 7
3.1 Basic rules . 7
3.2 Time scales. 8
3.3 Representations and format representations . 10
3.4 Characters used in the representations . 10
3.5 Expansion . 12
3.6 Leading zeros . 12
3.7 Mutual agreement . 12
4 Date and time representations. 13
4.1 Date. 13
4.2 Time of day . 15
4.3 Date and time of day. 18
4.4 Time interval . 20
4.5 Recurring time interval. 23
5 Date and time format representations . 25
Annex A (informative) Relationship to ISO 2014, ISO 2015, ISO 2711, ISO 3307 and ISO 4031 . 26
Annex B (informative) Examples of representations . 27
Bibliography . 33

Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies
(ISO member bodies). The work of preparing International Standards is normally carried out through ISO
technical committees. Each member body interested in a subject for which a technical committee has been
established has the right to be represented on that committee. International organizations, governmental and
non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the
International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International Standards
adopted by the technical committees are circulated to the member bodies for voting. Publication as an
International Standard requires approval by at least 75 % of the member bodies casting a vote.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. ISO shall not be held responsible for identifying any or all such patent rights.
ISO 8601 was prepared by Technical Committee ISO/TC 154, Processes, data elements and documents in
commerce, industry and administration.
This third edition cancels and replaces the second edition (ISO 8601:2000), of which it constitutes a minor
revision.
iv © ISO 2004 – All rights reserved

Introduction
Although ISO Recommendations and Standards in this field have been available since 1971, different forms of
numeric representation of dates and times have been in common use in different countries. Where such
representations are interchanged across national boundaries misinterpretation of the significance of the
numerals can occur, resulting in confusion and other consequential errors or losses. The purpose of this
International Standard is to eliminate the risk of misinterpretation and to avoid the confusion and its
consequences.
This International Standard includes specifications for a numeric representation of information regarding date
and time of day. In addition this International Standard includes specifications for representation of the formats
of these numeric representations.
In order to achieve similar formats for the representations of calendar dates, ordinal dates, dates identified by
week number, time intervals, recurring time intervals, combined date and time of day, and differences
between local time and UTC of day, and to avoid ambiguities between these representations, it has been
necessary to use, apart from numeric characters, either single alphabetic characters or other graphic
characters or a combination of alphabetic and other characters in some of the representations.
The above action has had the benefit of enhancing the versatility and general applicability of previous
International Standards in this field, and provides for the unique representation of any date or time expression
or combination of these. Each representation can be easily recognized, which is beneficial when human
interpretation is required.
This International Standard retains the most commonly used expressions for date and time of day and their
representations from the earlier International Standards and provides unique representations for some new
expressions used in practice. Its application in information interchange, especially between data processing
systems and associated equipment will eliminate errors arising from misinterpretation and the costs these
generate. The promotion of this International Standard will not only facilitate interchange across international
boundaries, but will also improve the portability of software, and will ease problems of communication within
an organization, as well as between organizations.
Several of the alphabetic and graphic characters used in the text of this International Standard are common
both to the representations specified and to normal typographical presentation. Note that for units of time in
plain text the symbols given in ISO 31-1 should be used.
To avoid confusion between the representations and the actual text, its punctuation marks and associated
graphic characters, all the representations are contained in brackets [ ]. The brackets are not part of the
representation, and should be omitted when implementing the representations. All matter outside the brackets
is normal text, and not part of the representation. In the associated examples, the brackets and typographical
markings are omitted.
INTERNATIONAL STANDARD ISO 8601:2004(E)

Data elements and interchange formats — Information
interchange — Representation of dates and times
1 Scope
This International Standard is applicable whenever representation of dates in the Gregorian calendar, times in
the 24-hour timekeeping system, time intervals and recurring time intervals or of the formats of these
representations are included in information interchange. It includes
 calendar dates expressed in terms of calendar year, calendar month and calendar day of the month;
 ordinal dates expressed in terms of calendar year and calendar day of the year;
 week dates expressed in terms of calendar year, calendar week number and calendar day of the week;
 local time based upon the 24-hour timekeeping system;
 Coordinated Universal Time of day;
 local time and the difference from Coordinated Universal Time;
 combination of date and time of day;
 time intervals;
 recurring time intervals.
This International Standard does not cover dates and times where words are used in the representation and
dates and times where characters are not used in the representation.
This International Standard does not assign any particular meaning or interpretation to any data element that
uses representations in accordance with this International Standard. Such meaning will be determined by the
context of the application.
2 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
2.1 Basic concepts
2.1.1
time axis
mathematical representation of the succession in time of instantaneous events along a unique axis
[IEC 60050-111]
2.1.2
instant
point on the time axis
[IEC 60050-111]
NOTE An instantaneous event occurs at a specific instant.
2.1.3
time interval
part of the time axis limited by two instants
[IEC 60050-111]
NOTE A time interval comprises all instants between the two limiting instants and, unless otherwise stated, the
limiting instants themselves.
2.1.4
time scale
system of ordered marks which can be attributed to instants on the time axis, one instant being chosen as the
origin
[IEC 60050-111]
NOTE 1 A time scale may amongst others be chosen as:
— continuous, e.g. international atomic time (TAI) (see IEC 60050-713, item 713-05-18);
— continuous with discontinuities, e.g. Coordinated Universal Time (UTC) due to leap seconds, standard time due to
summer time and winter time;
— successive steps, e.g. usual calendars, where the time axis is split up into a succession of consecutive time intervals
and the same mark is attributed to all instants of each time interval;
— discrete, e.g. in digital techniques.
NOTE 2 For physical and technical applications, a time scale with quantitative marks is preferred, based on a chosen
initial instant together with a unit of measurement.
NOTE 3 Customary time scales use various units of measurement in combination, such as second, minute, hour, or
various time intervals of the calendar such as calendar day, calendar month and calendar year.
NOTE 4 A time scale has a reference point which attributes one of the marks of the time scale to one of the instants,
thus determining the attribution of marks to instants for the time scale.
2.1.5
time point
date
time
mark attributed to an instant by means of a specified time scale
[IEC 60050-111]
NOTE 1 On a time scale consisting of successive steps, two distinct instants may be expressed by the same time point
(see Note 1 of the term “time scale”).
NOTE 2 For many time scales with quantitative marks, the numerical value of the time point of an instant may also be
considered to be equal to the duration between the origin of the time scale and the considered instant.
NOTE 3 In IEC 60050-111 this definition corresponds with the term “date”.
NOTE 4 The term “time” is often used in common language. However, it should only be used if the meaning is clearly
visible from the context, since the term “time” is also used with other meanings.
2.1.6
duration
non-negative quantity attributed to a time interval, the value of which is equal to the difference between the
time points of the final instant and the initial instant of the time interval, when the time points are quantitative
marks
[IEC 60050-111]
2 © ISO 2004 – All rights reserved

NOTE 1 In the case of discontinuities in the time scale, such as a leap second or the change from winter time to
summer time and back, the computation of the duration requires the subtraction or addition of the change of duration of
the discontinuity.
NOTE 2 Duration is one of the base quantities in the International System of Quantities (ISQ) on which the
International System of Units (SI) is based. The term “time” instead of “duration” is often used in this context.
NOTE 3 For the term “duration”, expressions such as “time” or “time interval” are often used. The term “time” is not
recommended in this sense and the term “time interval” is deprecated in this sense to avoid confusion with the concept
“time interval”.
NOTE 4 The SI unit of duration is the second.
2.1.7
nominal duration
duration expressed amongst others in years, months, weeks or days
NOTE The duration of a calendar year, a calendar month, a calendar week or a calendar day depends on its position
in the calendar. Therefore, the exact duration of a nominal duration can only be evaluated if the duration of the calendar
years, calendar months, calendar weeks or calendar days used are known.
2.1.8
date
time point representing a calendar day on a time scale consisting of an origin and a succession of calendar
days
NOTE In IEC 60050-111 this definition corresponds with the term “calendar date”.
2.1.9
calendar date
date representing a particular calendar day by its calendar year, its calendar month and its ordinal number
within its calendar month
2.1.10
ordinal date
date representing a particular calendar day by its calendar year and its ordinal number within its calendar year
2.1.11
week date
date representing a particular calendar day by the calendar year to which its calendar week belongs, the
ordinal number of its calendar week within that calendar year and its ordinal number within its calendar week
2.1.12
Coordinated Universal Time
UTC
time scale which forms the basis of a coordinated radio dissemination of standard frequencies and time
signals; it corresponds exactly in rate with international atomic time, but differs from it by an integral number of
seconds
[IEC 60050-713]
NOTE 1 UTC is established by the International Bureau of Weights and Measures (BIPM, i.e. Bureau International des
Poids et Mesures) and the International Earth Rotation Service (IERS). UTC provides the basis of standard time, the use
of which is legal in most countries. The 15th Conférence Géneral des Poids et Mesures (CGPM) (1975) judged in its
Resolution 5 that this usage can be strongly recommended.
NOTE 2 UTC is adjusted to UT1 by the insertion or deletion of seconds, known as “leap seconds”.
NOTE 3 Greenwich Mean Time (GMT) is internationally replaced by UTC. UTC is often (incorrectly) referred to as GMT.
UTC is generally used by aviation and maritime navigation that also uses local apparent time and local mean time for
celestial navigation (see ISO 19018).
NOTE 4 Additional information can be found as follows:
— the URL for the ITU http://www.itu.int/itudoc/itu-r/rec/tf/index.html
— the URL for the International Bureau of Weights and Measures http://www.bipm.fr
— the URL for the International Earth Rotation Service http://hpiers.obspm.fr.
2.1.13
UTC of day
quantitative expression marking an instant within a calendar day in accordance with UTC
2.1.14
standard time
time scale derived from coordinated universal time, UTC, by a time shift established in a given location by the
competent authority
[IEC 60050-111]
NOTE This time shift may be varied in the course of a year.
2.1.15
standard time of day
quantitative expression marking an instant within a calendar day by the duration elapsed after midnight in the
local standard time
[IEC 60050-111]
NOTE Standard time of day is called “clock time” in IEC 60050-111.
2.1.16
local time
locally applicable time of day such as standard time of day, or a non-UTC based time of day
2.1.17
recurring time interval
series of consecutive time intervals of the same duration or nominal duration
NOTE If the duration of the time intervals is measured in calendar entities, the duration of each time interval depends
on the calendar dates of its start and its end.
2.2 Time units, nominal durations and time intervals
2.2.1
second
base unit of measurement of time in the International System of Units (SI) as defined by the International
Committee of Weights and Measures (CIPM, i.e. Comité International des Poids et Mesures)
NOTE 1 See also ISO 31-1.
NOTE 2 It is the base unit for expressing duration.
2.2.2
leap second
intentional time step of one second to adjust UTC to ensure appropriate agreement with UT1, a time scale
based on the rotation of the Earth
[Rec. ITU-R TF.460-5]
NOTE An inserted second is called positive leap second and an omitted second is called negative leap second. A
positive leap second is inserted between [23:59:59Z] and [24:00:00Z] and can be represented as [23:59:60Z]. Negative
leap seconds are achieved by the omission of [23:59:59Z]. Insertion or omission takes place as determined by IERS,
normally on 30 June or 31 December, but if necessary on 31 March or 30 September.
4 © ISO 2004 – All rights reserved

2.2.3
minute
unit of time, equal to 60 seconds
[ISO 31-1]
2.2.4
hour
unit of time, equal to 60 minutes
[ISO 31-1]
2.2.5
day
〈unit of time〉 unit of time, equal to 24 hours
[ISO 31-1]
2.2.6
calendar day
time interval starting at midnight and ending at the next midnight, the latter being also the starting instant of
the next calendar day
NOTE 1 A calendar day is often also referred to as day.
NOTE 2 The duration of a calendar day is 24 hours; except if modified by:
— the insertion or deletion of leap seconds, by decision of the International Earth Rotation Service (IERS), or
— the insertion or deletion of other time intervals, as may be prescribed by local authorities to alter the time scale of local
time.
2.2.7
day
〈duration〉 duration of a calendar day
NOTE The term “day” applies also to the duration of any time interval which starts at a certain time of day at a certain
calendar day and ends at the same time of day at the next calendar day.
2.2.8
calendar week
time interval of seven calendar days starting with a Monday
NOTE 1 A calendar week is often also referred to as week.
NOTE 2 See 3.2.2 for the names of the calendar days and their day numbers.
NOTE 3 A calendar week may be identified by its ordinal number within its calendar year.
2.2.9
week
duration of a calendar week
NOTE The term “week” applies also to the duration of any time interval which starts at a certain time of day at a
certain calendar day and ends at the same time of day at the same calendar day of the next calendar week.
2.2.10
calendar week number
ordinal number which identifies a calendar week within its calendar year according to the rule that the first
calendar week of a year is that one which includes the first Thursday of that year and that the last calendar
week of a calendar year is the week immediately preceding the first calendar week of the next calendar year
2.2.11
calendar month
time interval resulting from the division of a calendar year in 12 time intervals, each with a specific name and
containing a specific number of calendar days
NOTE 1 A calendar month is often referred to as month.
NOTE 2 See 3.2.1 for the names of the months of the calendar year in the Gregorian calendar, listed in their order of
occurrence, for their number of days, and for the ordinal dates of the days in common and leap years.
2.2.12
month
duration of 28, 29, 30 or 31 calendar days depending on the start and/or the end of the corresponding time
interval within the specific calendar month
NOTE 1 The term “month” applies also to the duration of any time interval which starts at a certain time of day at a
certain calendar day of the calendar month and ends at the same time of day at the same calendar day of the next
calendar month, if it exists. In other cases the ending calendar day has to be agreed on.
NOTE 2 In certain applications a month is considered as a duration of 30 calendar days.
2.2.13
calendar year
cyclic time interval in a calendar which is required for one revolution of the Earth around the Sun and
approximated to an integral number of calendar days
NOTE 1 A calendar year is often also referred to as year.
NOTE 2 Unless otherwise specified the term designates in this International Standard a calendar year in the Gregorian
calendar.
2.2.14
year
duration of 365 or 366 calendar days depending on the start and/or the end of the corresponding time interval
within the specific calendar year
NOTE The term “year” applies also to the duration of any time interval which starts at a certain time of day at a
certain calendar date of the calendar year and ends at the same time of day at the same calendar date of the next
calendar year, if it exists. In other cases the ending calendar date has to be agreed on.
2.2.15
Gregorian calendar
calendar in general use, introduced in 1582 to define a calendar year that more closely approximated the
tropical year than the Julian calendar
NOTE In this International Standard the term Gregorian calendar is used to refer to the time scale described in 3.2.1.
2.2.16
common year
calendar year in the Gregorian calendar that has 365 calendar days
2.2.17
leap year
calendar year in the Gregorian calendar that has 366 calendar days
2.2.18
centennial year
calendar year in the Gregorian calendar whose year number is divisible without remainder by hundred
6 © ISO 2004 – All rights reserved

2.3 Representations and formats
2.3.1
date and time representation
expression indicating a time point, time interval or recurring time interval
2.3.2
date and time format representation
expression describing the format of a group of date and time representations
2.3.3
basic format
format of a date and time representation or date and time format representation comprising the minimum
number of time elements necessary for the accuracy required
NOTE The basic format should be avoided in plain text.
2.3.4
extended format
extension of the basic format that includes additional separators
2.3.5
complete representation
representation that includes all the date and time components associated with the expression; limited, if
applicable, for time elements of representations expressing a calendar year to four digits
2.3.6
decimal representation
expansion of a representation by addition of a decimal fraction to the lowest order component of the
expression
2.3.7
representation with reduced accuracy
abbreviation of a representation by omission of lower order components
2.3.8
expanded representation
expansion of a representation to allow identification of dates in calendar years outside the range [0000] till
[9999]
3 Fundamental principles
3.1 Basic rules
This International Standard gives a set of rules for the representation of
 time points,
 time intervals,
 recurring time intervals.
Both accurate and approximate representations can be identified by means of unique and unambiguous
expressions specifying the relevant dates, times of day and durations. The degree of accuracy required and
obtainable can be varied by including or deleting the appropriate time elements (such as seconds).
In addition, this International Standard gives rules for the representation of expressions describing the format
of the above representations.
The decreasing order of time elements, left-to-right, is common to these representations.
3.2 Time scales
3.2.1 The Gregorian calendar
This International Standard uses the Gregorian calendar for the identification of calendar days. This calendar
provides a time scale consisting of a, potentially infinite, series of contiguous calendar years. Consecutive
calendar years are identified by sequentially assigned year numbers.
The Gregorian calendar distinguishes common years of 365 consecutive calendar days and leap years of 366
consecutive calendar days. A leap year is a year whose year number is divisible by four an integral number of
times. However, a centennial year is not a leap year unless its year number is divisible by four hundred an
integral number of times.
In the Gregorian calendar each calendar year is divided in 12 sequential calendar months, each consisting of
a specific number of calendar days as indicated in Table 1.
The Gregorian calendar has a reference point that assigns 20 May 1875 to the calendar day that the
“Convention du Mètre” was signed in Paris.
This International Standard allows the identification of calendar years by their year number for years both
before and after the introduction of the Gregorian calendar. For the determination of calendar years, the year
number and the calendar day within the calendar year only the rules mentioned above are used. For the
purposes of this International Standard the calendar based on these rules is referred to as the Gregorian
calendar. The use of this calendar for dates preceding the introduction of the Gregorian calendar (also called
the proleptic Gregorian calendar) should only be by agreement of the partners in information interchange.
The introduction of the Gregorian calendar included the cancellation of the accumulated inaccuracies of the
Julian calendar. However, no dates shall be inserted or deleted when determining dates in the proleptic
Gregorian calendar.
NOTE In the proleptic Gregorian calendar, the calendar year [0000] is a leap year.
EXAMPLE The Gregorian calendar was introduced on 15 October 1582. In the calendar set by this standard the
calendar day preceding that calendar day is referred to as 14 October 1582. In the Julian calendar that calendar day is
referred to as 4 October 1582.
8 © ISO 2004 – All rights reserved

Table 1 — Calendar months
Calendar month Calendar month Number of days in Ordinal dates of the days in Ordinal dates of the
number name the month common years days in leap years
01 January 31 001-031 001-031
02 February 032-059 032-060
(leap year 29)
03 March 31 060-090 061-091
04 April 30 091-120 092-121
05 May 31 121-151 122-152
06 June 30 152-181 153-182
07 July 31 182-212 183-213
08 August 31 213-243 214-244
09 September 30 244-273 245-274
10 October 31 274-304 275-305
11 November 30 305-334 306-335
12 December 31 335-365 336-366

3.2.2 The week calendar
This International Standard allows the use of the week calendar time scale for the identification of calendar
days.
This time scale is based on an unbounded series of contiguous calendar weeks. The calendar week number
identifies the calendar week within the calendar year. Each calendar week has seven calendar days as
indicated in Table 2.
The reference point of the time scale assigns Saturday to 1 January 2000.
Table 2 — Calendar days
Ordinal day number in
Calendar day name
the week
1 Monday
2 Tuesday
3 Wednesday
4 Thursday
5 Friday
6 Saturday
7 Sunday
NOTE 1 A calendar year has 52 or 53 calendar weeks.
NOTE 2 The first calendar week of a calendar year includes up to three days from the previous calendar year; the last
calendar week of a calendar year includes up to three days from the following calendar year. Therefore, for certain
calendar days the calendar date contains a different calendar year than the week date. For instance:
— Sunday 1 January 1995 is identified by the calendar date [1995-01-01] and week date [1994-W52-7]
— Tuesday 31 December 1996 is identified by the calendar date [1996-31-12] and week date [1997-W01-2].
NOTE 3 The rule for determining the first calendar week (see the definition of calendar week number in Clause 2) is
equivalent with the rule “the first calendar week is the calendar week which includes 4 January”.
3.2.3 Time scales within the calendar day
This International Standard recommends the use of time scales applying the 24-hour time keeping system for
the identification of time points within a calendar day.
These time scales provide marks which, except in case of discontinuities, represent the duration elapsed after
the start of the calendar day. In this International Standard these marks, which are collectively referred to as
time of day, are represented by the number of hours elapsed after midnight, the number of minutes elapsed
after the last full hour, the number of seconds elapsed after the last full minute, with decimal parts of a second
if necessary.
3.3 Representations and format representations
This International Standard defines date and time representations to express time points, time intervals and
recurring time intervals.
EXAMPLE The date and time representation [2003-02-10] identifies 10 February 2003.
To define the date and time representations permitted by this International Standard, use is made of date and
time format representations in which specific characters are used to represent digits or other characters in
date and time representations. A date and time format representation, together with its description, defines
permitted date and time representations.
EXAMPLE The date and time format representation [YYYY-MM-DD], together with the associated description,
defines the complete, extended format, calendar date representations permitted by this International Standard.
By mutual agreement the parties in information interchange may transfer the date and time format
representations. Only the date and time format representations permitted by this International Standard shall
be used.
The date and time format representations use characters that potentially expand into more than one character
in the date and time representation; this is indicated by underlining. If at the time of information interchange of
the date and time format representation the number of characters to be used in the date and time
representation is known, the variable expansion representation (i.e. underlining) shall not be used.
EXAMPLE Local time with three decimals for the fraction of the seconds is represented by [hh:mm:ss,sss], not by
[hh:mm:ss,s].
3.4 Characters used in the representations
3.4.1 Introduction
The representations specified in this International Standard make use of graphic characters as specified in 3.4.
Note that, except for “hyphen”, “minus” and “plus-minus”, these characters are part of the ISO/IEC 646
repertoire.
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”.
In an environment where use is made of the ITU-T S.1 repertoire (e.g. telex) date and time format
representations shall not be used.
In date and time format representations underlining of characters is used. In environments that do not support
the representation of underlined characters, the underline shall precede the character to be underlined.
10 © ISO 2004 – All rights reserved

NOTE 1 In date and time representations lower case characters may be used when upper case characters are not
available.
NOTE 2 Encoding of characters for the interchange of dates and times is not in the scope of this International Standard.
Unless explicitly allowed by this International Standard the character “space” shall not be used in the
representations.
3.4.2 Characters used in place of digits or signs
In date and time format representations characters are used to represent characters in the date and time
representations as follows:
[Y] represents a digit used in the time element “year”;
[M] represents a digit used in the time element “month”;
[D] represents a digit used in the time element “day”;
[w] represents a digit used in the time element “week”;
[h] represents a digit used in the time element “hour”;
[m] represents a digit used in the time element “minute”;
[s] represents a digit used in the time element “second”;
[n] represents a digit from a positive integer or zero;
[±] represents a plus sign [+] if in combination with the following element a positive value or zero needs
to be represented (in this case, unless explicitly stated otherwise, the plus sign shall not be omitted),
or a minus sign [−] if in combination with the following element a negative value needs to be
represented.
In addition the following convention applies:
[_] When any of the characters representing a digit is underlined, it represents zero or more digits in the
corresponding date and time representation.
Other characters in the date and time format representations are copied in the date and time representations.
3.4.3 Characters used as designators
In representations the following characters are used as designators:
[P] is used as duration designator, preceding the component which represents the duration;
NOTE The use of the character P is based on the historical use of the term “period” for duration.
[R] is used as recurring time interval designator;
[T] is used as time designator to indicate:
 the start of the representation of local time to designate local time expressions as such,
 the start of the representation of the time of day in date and time of day expressions,
 the start of the representation of the number of hours, minutes or seconds in expressions of duration;
[W] is used as week designator, preceding a data element which represents the ordinal number of a
calendar week within the calendar year;
[Z] is used as UTC designator.
In representations of duration (4.4.3.2), the following designators are used as part of the expression:
[Y] [M] [W] [D] [H] [M] [S]
NOTE 1 In these expressions, [M] may be used to indicate “month” or “minute”, or both.
NOTE 2 In date and time format representations the interpretation of the characters [Y], [M] and [D] as characters used
in place of digits or as designators depends on their position in the expression.
NOTE 3 These designators are used for the designation of units of time and nominal durations in the representations
defined in this International Standard. For the designation of units of time and durations in other contexts ISO 31-1 should
be applied.
3.4.4 Characters used as separators
In representations the following characters are used as separators:
[-] (hyphen): to separate the time elements “year” and “month”, “year” and “week”, “year” and “day”,
“month” and “day”, and “week” and “day”;
[:] (colon): to separate the time elements “hour” and “minute”, and “minute” and “second”;
[/] (solidus): to separate components in the representation of time intervals and recurring time intervals.
NOTE Representations defined in this International Standard also make use of the decimal separator.
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].
3.6 Leading zeros
If a time element in a defined representation has a defined length, then leading zeros shall be used as
required.
3.7 Mutual agreement
Some of the representations identified in this International Standard are only allowed by mutual agreement of
the partners in information interchange. Such agreement should ensure that fields in which the representation
may occur are not allowed to hold other representations that cannot be unambiguously distinguished from the
agreed representation.
12 © ISO 2004 – All rights reserved

4 Date and time representations
4.1 Date
4.1.1 General
For ease of comparison, in all the following examples of representations of dates, the date of 12 April 1985 is
used as an illustration, if applicable.
4.1.2 Calendar date
4.1.2.1 General
In expressions of calendar dates
 calendar year is, unless specified otherwise, represented by four digits. Calendar years are numbered in
ascending order according to the Gregorian calendar by values in the range [0000] to [9999]. Values in
the range [0000] through [1582] shall only be used by mutual agreement of the partners in information
interchange.
 calendar month is represented by two digits. January is represented by [01], and subsequent calendar
months are numbered in ascending sequence.
 calendar day of the month is represented by two digits. The first calendar day of any calendar month is
represented by [01] and subsequent calendar days of the same calendar month are numbered in
ascending sequence.
4.1.2.2 Complete representations
When the application identifies the need for a complete representation of a calendar date, it shall be one of
the numeric expressions as follows, where [YYYY] represents a calendar year, [MM] the ordinal number of a
calendar month within the calendar year, and [DD] the ordinal number of a calendar day within the calendar
month.
Basic format: YYYYMMDD Example: 19850412
Extended format: YYYY-MM-DD Example: 1985-04-12
4.1.2.3 Representations with reduced accuracy
If in a given application it is sufficient to express a calendar date with less accuracy than a complete
representation as specified in 4.1.2.2, either two, four or six digits may be omitted, the omission starting from
the extreme right-hand side. The resulting representation will then indicate a month, a year or a century, as
set out below. When only [DD] is omitted, a separator shall be inserted between [YYYY] and [MM], but
separators shall not be used in the other representations with reduced accuracy.
a) A specific month
Basic format: YYYY-MM Example: 1985-04
Extended format: not applicable
b) A specific year
Basic format: YYYY Example: 1985
Extended format: not applicable
c) A specific century
Basic format: YY Example: 19
Extended format: not applicable
4.1.2.4 Expanded representations
If, by agreement, expanded representations are used, the formats shall be as specified below. The
interchange parties shall agree the additional number of digits in the time element year. In the examples below
it has been agreed to expand the time element year with two digits.
a) A specific day
Basic format: ±YYYYYMMDD Example: +0019850412
Extended format: ±YYYYY-MM-DD Example: +001985-04-12
b) A specific month
Basic format: ±YYYYY-MM Example: +001985-04
Extended format: not applicable
c) A specific year
Basic format: ±YYYYY Example: +001985
Extended format: not applicable
d) A specific century
Basic format: ±YYY Example: +0019
Extended format: not applicable
NOTE 4.1.2.4 includes the definition of representations that are expanded and have reduced accuracy.
4.1.3 Ordinal date
4.1.3.1 General
In expressions of ordinal dates
 calendar year is represented as in 4.1.2.
 calendar day of the year is represented by three decimal digits. The first calendar day of any calendar
year is represented by [001] and subsequent calendar days are numbered in ascending sequence.
4.1.3.2 Complete representations
When the application identifies the need for a complete representation of an ordinal date, it shall be one of the
numeric expressions as follows, where [YYYY] represents a calendar year and [DDD] the ordinal number of a
calendar day within the calendar year.
Basic format: YYYYDDD Example: 1985102
Extended format: YYYY-DDD Example: 1985-102
4.1.3.3 Expanded representations
If, by agreement, expanded representations are used the formats shall be as specified below. The interchange
parties shall agree the additional number of digits in the time element year. In the examples below it has been
agreed to expand the time element year with two digits.
A specific day
Basic format: ±YYYYYDDD Example: +001985102
Extended format: ±YYYYY-DDD Example: +001985-102
14 © ISO 2004 – All rights reserved

4.1.4 Week date
4.1.4.1 General
In expressions of week dates
 calendar year is represented as in 4.1.2.
 calendar week is represented by two decimal digits. The first calendar week of a year shall be identified
as [01] and subsequent weeks shall be numbered in ascending sequence.
 calendar day of the week is represented by one decimal digit. Monday shall be identified as calendar
day [1] of any calendar week, and subsequent calendar days of the same calendar week shall be
numbered in as
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