Editing ISO 8601 (section)

===Time zone designators===
{| class="infobox" style="text-align:center; width:23em"
|-
| &lt;time&gt;Z
|-
| &lt;time&gt;±hh:mm
|-
| &lt;time&gt;±hhmm
|-
| &lt;time&gt;±hh
|}

[[Time zone]]s in ISO&nbsp;8601 are represented as local time (with the location unspecified), as [[UTC]], or as an offset from UTC.

====Local time (unqualified)====
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)====
If the time is in [[Coordinated Universal Time|UTC]], add a ''Z'' directly after the time without a space. ''Z'' is the zone designator for the zero UTC offset. "09:30 UTC" is therefore represented as "09:30Z" or "T0930Z". "14:45:15 UTC" would be "14:45:15Z" or "T144515Z".

The ''Z'' suffix in the ISO&nbsp;8601 time representation is sometimes referred to as "Zulu time" or "Zulu meridian" because the same letter is used to designate the [[List of military time zones|Zulu time zone]].<ref>{{Cite web |last=Markus Kuhn |date=2020-06-16 |title=A summary of the international standard date and time notation |url=https://www.cl.cam.ac.uk/~mgk25/iso-time.html |url-status=live |archive-url=https://web.archive.org/web/20221005210715/https://www.cl.cam.ac.uk/~mgk25/iso-time.html |archive-date=2022-10-05 |access-date=2022-10-05}}</ref> 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]]<ref name="ACP_121_I">{{Cite web |last=<!--Not stated--> |date=October 2010 |title=Communication Instructions General ACP 121(I) |url=https://rnzncomms.files.wordpress.com/2016/10/acp121_i_2010.pdf |url-status=live |archive-url=https://web.archive.org/web/20180116081251/https://rnzncomms.files.wordpress.com/2016/10/acp121_i_2010.pdf |archive-date=2018-01-16 |access-date=2018-01-15 |publisher=[[Combined Communications Electronics Board]]}}</ref> 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.<ref>{{Cite book |last1=McCarthy |first1=Dennis D. |author-link1=Dennis D. McCarthy |title=Time: From Earth Rotation to Atomic Physics |last2=Seidelmann |first2=Kenneth P. |publisher=[[Wiley-VCH Verlag GmbH & Co. KGaA]] |year=2009 |isbn=978-3-527-40780-4 |location=Weinheim |page=10}}</ref>

====Time offsets from UTC====
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 (city)|New York]] (on [[standard time]]) would be "&minus;05:00","&minus;0500", or "&minus;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 "[[UTC+00:00|+00:00]]", "[[UTC+00:00|+0000]]", or "[[UTC+00:00|+00]]".

=====Additional examples=====
* "[[UTC-10:00|&minus;10:00]]" for [[Honolulu]]
* "[[UTC-06:00|&minus;06:00]]" for [[Chicago]] on [[standard time]], or [[Denver]] on [[daylight saving time]]
* "[[UTC-03:00|&minus;03:00]]" for [[Brasília]]
* "[[UTC+01:00|+01:00]]" for [[London]] on [[British Summer Time]]
* "[[UTC+04:00|+04:00]]" for [[Dubai]]
* "[[UTC+05:30|+05:30]]" for [[India]]
* "[[UTC+09:00|+09:00]]" for [[Japan]]
See [[List of UTC offsets]] for other [[UTC offset]]s.

=====Other time offset specifications=====
It is not permitted to state a zero value time offset with a negative sign, as "&minus;00:00", "&minus;0000", or "&minus;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|plus-minus-sign ({{char|&pm;}})]] may also be used if it is available.<ref>ISO 8601-1:2019 section 3.2.4, ISO 8601:2004 section 3.4.2</ref> 

Contrary to this rule, RFC 3339, which is otherwise a profile of ISO&nbsp;8601, permits the use of "&minus;00" with the same denotation as "+00" but a differing connotation: an unknown [[UTC offset]].<ref>RFC 3339{{spaced ndash}}Unknown local offset convention</ref><ref>{{Cite IETF|last=Newman|first=Chris|editor-last=Klyne|editor-first=Graham|title=Date and Time on the Internet:Timestamps |sectionname=Unknown Local Offset Convention|date=July 2002|rfc=3339|section=4.3|access-date=1 February 2021|publisher=[[Internet Engineering Task Force|IETF]] |quote=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}}</ref>

To represent a negative offset, ISO&nbsp;8601 specifies using a [[minus sign]] ({{char|&minus;}}). If the interchange character set is limited and does not have a minus sign character, then the [[hyphen-minus]] should be used ({{char|-}}).<ref>{{cite ISO standard|title=Data elements and interchange formats — Information interchange - Representation of dates and times — Part 1: Basic rules|id=ISO/WD 8601-1|page=12|sectionname=Characters used in the representations - Introduction|section=3.4.1 Characters used in the representations - Introduction|publisher=[[International Organization for Standardization|ISO]]|date=2016-02-16|url=https://www.loc.gov/standards/datetime/iso-tc154-wg5_n0038_iso_wd_8601-1_2016-02-16.pdf|type=pdf|archive-url=https://archive.today/20221005210840/https://www.loc.gov/standards/datetime/iso-tc154-wg5_n0038_iso_wd_8601-1_2016-02-16.pdf|archive-date=2022-10-05|url-status=live|quote=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"}}</ref> [[ASCII]] does not have a minus sign, so its hyphen-minus character (code 45<sub>10</sub>) would be used. If the character set has a minus sign, such as {{unichar|2212|minus sign}} in [[Unicode]], then that character should be used. The [[HTML entity|HTML character entity]] invocation for {{char|&minus;}} is <code>&amp;minus;</code>.

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 '<nowiki><time>±[hh]:[mm]:[ss].[sss]' or '<time>±[n]H[n]M[n]S' as below.</nowiki>