Date and time formats

January 28, 2008

Did you know there’s an international standard for date and time formats? It eliminates the confusion that arises when dates in one format are viewed by people in another country who use a different format. For example, to me (in Australia), 4/5/2008 is the 4th of May, 2008, but to someone in the US, this is the 5th of April, 2008—quite a different date.

In essence, the standard says to write dates and times from largest to smallest, so yyyy-mmm-dd for dates and hh:mm:ss for time.

The standard is ISO 8601 and you can find out more about it here:

In the December 2002 CyberText Newsletter, I also wrote about this standard for date formats. Here’s some additional information from that article:

For ease of use in sorting, filing and retrieving computer documents, [using this date format] is a preferred method. It is also simpler for calculating elapsed time, and combines naturally with the big-to-small convention used for hh mm ss when you need to be more specific about a date/time.

Because we should be writing in such a way that we don’t exclude parts of our audience, we should be using a date convention that is globally acceptable—we don’t have to say our dates this way, but we should be using this format in our professional communications, such as letters, faxes, and the like.

See also:


  1. Hi Rhonda, I finally read this post you referenced in your message to the STCCIC mailing list. I remember reading about yyyy-mm-dd being an international standard several years ago, but I had already standardized on that format for myself several years before that.

    This format, with or without dashes, in addition to being explicitly clear in its meaning, is very effective for naming folders, files, and even my invoices so that they sort chronologically.

    Thanks for all that you do!

  2. Rhonda,
    Since 2010 Jan 1 I have been using the following number formats to sequence files produced each day.

    This system is good for a year.

    For one that will be good for 10 years

    ..Bruce White..

  3. […] ISO date and time formats: https://cybertext.wordpress.com/2008/01/28/date-and-time-formats/ […]

  4. […] 4/9/2012 (this format is the LEAST ACCEPTABLE as it will be misread by US readers as 9 April 2012. The Style Manual [p171] says: ‘All-numeral forms of dates can mislead because international practice varies, so ISO 8601:2000 should be followed in documents for wide distribution.’ [Note: ISO 8601:2000 specifies writing all-numeral dates in YYYYMMDD format, so 4 September 2012 would be 20120904; see also: https://cybertext.wordpress.com/2008/01/28/date-and-time-formats/%5D), […]

  5. […] short or long form so that it’s absolutely clear which date you mean. While you could use the ISO format for dates, the reality is that these aren’t easily readable, so if you go the more informal route, then […]

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