ISO 8601

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The International Standards Organisation's standard, number 8601 is an international standard for date and time representations. It is used for all date-time representations in microformats, as well as a number of other formats (HTML5 <time> element & datetime attribute, XML Schema Datatypes, RDF, Atom).


Image: XKCD

In addition, ISO 8601 dates in particular are the most globally unambiguously human readable/writeable date format and thus should always be used on the (world wide) web.


The following are good prose overviews of ISO 8601:


microformats in general use a subset of ISO8601 - preferring uses which are more human readable (requiring hyphens in dates, and colons in times).

All date-time properties in microformats use ISO8601 values. E.g.


HTML5 uses both a subset of ISO 8601 for dates, times, durations for the <time> element, as well as an extended (and more human friendly) duration format.

RFC 3339

RFC 3339 defines a profile of ISO 8601 for the use in Internet protocols and standards.

  • It explicitly excludes durations and dates before the common era.
  • The more complex formats like week numbers and ordinal day are not permitted (see RFC 3339, section 5.6).

ISO 8601 implementations in programming libraries

  • JodaTime - the Java date-time library - ISO8601 Java calendar system
  • Perl: DateTime::Format::ISO8601
  • Ruby 1.9 implements an iso8601 method in the Date STDLIB but it does not handle ordinal dates.
  • Glenn Jones' microformat-node parser includes isodate.js, a Node.js implementation of (some of) ISO 8601.
  • Python: iso8601

to do! document more implementations.


Why hyphens in dates

Q: Must I use the hyphens?[1]

A: You should always use hyphens in ISO 8601 dates because that makes them more readable, and thus more human friendly.

Also, using hyphens helps clearly distinguish different uses for different granularities of dates, e.g.:

  • 2013-08-19 - just the day
  • 2013-08 - the whole month
  • 2013 - the entire year


None currently.

Resolved issues: iso-8601-issues-resolved.

See also

Related pages