Extended Date Time Format
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EDTF - The Extended Date/Time Format - defines features to be supported in a date/time string, features considered useful for a wide variety of applications

Basic date and time formats are specified in ISO 8601-2004, the International Standard for the representation of dates and times. ISO 8601-2004 is not sufficiently expressive to support various semantic qualifiers and concepts than many applications find useful. For example, although it can express the concept "the year 1984", it cannot express "approximately the year 1984", or "we think the year is 1984 but we're not certain". These as well as various other concepts are therefore often represented using ad hoc conventions; EDTF provides a standard syntax for their representation. Further, 8601 is a complex specification describing a large number of date/time formats, in many cases providing multiple options for a given format. Thus a second aim of EDTF is to restrict the supported formats to a smaller set.

EDTF was developed over the course of several years by a community of interested parties, via a listserv, which is still in operation; join the discussion. A Draft Specification was published in 2012. A number of implementers have developed prototype implementations.


The draft specification is to be superceded; EDTF functionality has been integrated into a draft revision of ISO 8601 to be published in 2017 or 2018.


The revision of ISO 8601 consists of two parts. Part 1 is essentially the same as 8601-2004 (with some corrections). Part 2 will be extensions, one of which is EDTF. The full functionality of the draft specification is retained, however several syntactic changes were necessary, to satisfy international requirements.

ISO 8601-201x is at DIS (Draft International Standard) stage and is currently under ballot.

The DIS documents for parts 1 and 2 are available:

          ISO DIS 8601 Part 1    |   1SO DIS 8601 Part 2

For EDTF see Part 2, Clause 4 and Annex C.

As of January 16, 2018, at the request of ISO, the above two links have been removed and the two documents taken down.

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