Date and Time Formats ISO 8601 International Standard

The SEO Consultants Directory utilizes the ISO 8601 date and time format and have been for quite some time. We've found that any and all issues previously associated with our regionally specific date and time formats were negated once we made the switch to ISO 8601. Since our directory is appealing to an International audience, our regionally specific date and time formats may have been misunderstood by many outside of the United States.

While we agree that some may find the ISO 8601 date and time formats a little confusing, we hope that after reading this section along with information from the authoritative resources we've provided links to, that you'll consider making the change and adhering to the ISO 8601 standards. We feel this is a long term strategy and one that will benefit all who are following standards.

From the W3C

This document defines a profile of ISO 8601, the International Standard for the representation of dates and times. ISO 8601 describes a large number of date/time formats. To reduce the scope for error and the complexity of software, it is useful to restrict the supported formats to a small number. This profile defines a few date/time formats, likely to satisfy most requirements.


Different standards may need different levels of granularity in the date and time, so this profile defines six levels. Standards that reference this profile should specify one or more of these granularities. If a given standard allows more than one granularity, it should specify the meaning of the dates and times with reduced precision, for example, the result of comparing two dates with different precisions.

The formats are as follows. Exactly the components shown here must be present, with exactly this punctuation. Note that the "T" appears literally in the string, to indicate the beginning of the time element, as specified in ISO 8601.

   YYYY (e.g. 2004)
   YYYY-MM (e.g. 2004-06)
Complete date:
   YYYY-MM-DD (e.g. 2004-06-01)
Complete date:hours:minutes
   YYYY-MM-DDThh:mmTZD (e.g. 2004-06-01T19:20+01:00)
Complete date:hours:minutes:seconds
   YYYY-MM-DDThh:mm:ssTZD (e.g. 2004-06-01T19:20:30+01:00)
Complete date:hours:minutes:seconds:decimal fraction of a second
   YYYY-MM-DDThh:mm:ss.sTZD (e.g. 2004-06-01T19:20:30.45+01:00)

Explanation of the above formatting:

YYYY = four-digit year
MM   = two-digit month (01=January, etc.)
DD   = two-digit day of month (01 through 31)
hh   = two digits of hour (00 through 23) (am/pm NOT allowed)
mm   = two digits of minute (00 through 59)
ss   = two digits of second (00 through 59)
s    = one or more digits representing a decimal fraction of a second
TZD  = time zone designator (Z or +hh:mm or -hh:mm)

This profile does not specify how many digits may be used to represent the decimal fraction of a second. An adopting standard that permits fractions of a second must specify both the minimum number of digits (a number greater than or equal to one) and the maximum number of digits (the maximum may be stated to be "unlimited").

This profile defines two ways of handling time zone offsets:

  1. Times are expressed in UTC (Coordinated Universal Time), with a special UTC designator ("Z").
  2. Times are expressed in local time, together with a time zone offset in hours and minutes. A time zone offset of "+hh:mm" indicates that the date/time uses a local time zone which is "hh" hours and "mm" minutes ahead of UTC. A time zone offset of "-hh:mm" indicates that the date/time uses a local time zone which is "hh" hours and "mm" minutes behind UTC.

A standard referencing this profile should permit one or both of these ways of handling time zone offsets.



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