We don’t take kindly to our sleep being disrupted in the wee hours by a selfie from friends sharing their latest updates from their holiday on a far-flung beach resort. But when it comes to doing business in today’s hyperconnected world, late-night grumpiness can leave you with serious egg on your face.

From making sure your online calendar is in sync for virtual meetings with colleagues in other time zones, to scheduling video conference calls, not to mention turning up for face-to-face meetings on the right day after a long-haul flight, if you want to be taken seriously in a highly competitive world, it is not acceptable to get the date and the time wrong.  

Luckily, there is an International Standard to ensure this doesn’t happen. ISO 8601:2019, Date and time – Representations for information interchange, is a two-part standard supported by all modern programming languages. Part 1 – Basic rules is the functional replacement for the 2004 version of the standard, while Part 2 – Extensions, as the title suggests, extends Part 1 with a new functionality.

The standard not only facilitates interchange across international boundaries, but also improves the portability of software, and will ease problems of communication within an organization and between organizations.

Ray Denenberg, from the Library of Congress in the USA, Project Leader, and Convenor of working group WG 5, says: “Part 1 – Basic rules is the functional replacement for the 2004 version of the standard: representations for date, time, duration and interval. Some previous areas of confusion – most notably end/beginning of day – have been clarified, and definitions and references have been brought up to date.”

The new functionality in Part 2, Extensions, Denenberg says, includes semantic qualifiers and concepts, “for example, uncertain or approximate dates, dates with portions unspecified, seasons and other divisions of a year, and set representation, based on the extended date/time format (EDTF) developed at the Library of Congress”.

“Additional extensions,” he says, “include methods to specify repeat rules for a recurring interval, selection rules, date and time arithmetic, and a new explicit representation format based on CalConnect standards1) and adapted by Ronald Tse, WG 5 Convenor-elect.”

ISO 8601-1:2019 and ISO 8601-2:2019 were developed by ISO technical committee ISO/TC 154, Processes, data elements and documents in commerce, industry and administration, whose secretariat is held by SAC, ISO’s member for China. It is available from your national ISO member or through the ISO Store.


1) A CalConnect standard is a normative document that has gone through the Calendaring and Scheduling Consortium standardization process.