ISO 8601 Date Formatting

The information presented here is a quick reference adapted from Wikipedia’s ISO 8601 article to describe the formats used in this site.

Dates and Times

Dates are presented in YYYY-MM-DD format.

Times are presented in 24-hour hh:mm format. The specification includes a leading T character, but it is omitted here. The specification also permits the omission of minutes if a time occurs at the “top of the hour,” but doing so can lead to confusion; so minutes are included with all formatted times.

When combined, the date and time elements are separated by a space to improve readability, i.e., YYYY-MM-DD hh:mm, rather than the specified T character.


Times are typically represented in local time, which for this site is Central Time (UTC-06:00, or UTC-05:00 during Daylight Savings Time).

However, if specific time zone information is important for some reason, then times will likely include the offset suffix, e.g., -06:00, or be given in UTC with a Z suffix.

For example, 2023-03-05 12:00 can be considered equivalent to 2023-03-05 12:00-06:00 and 2023-03-05 18:00Z.

The use of a - character for this information necessitates a seemingly odd format for encoding intervals.


Weekdays are not mentioned in the official ISO 8601 specification outside of using a “week-numbering year,” but if they are included as part of the content in this site, they will be either:

  1. mentioned before the date, e.g., Sunday, 2023-03-05 12:00; or

  2. abbreviated after the date, e.g., 2023-03-05 (U) 12:00.

The abbreviations that might be used:

Weekday 1-letter 2-letter 3-letter
Sunday U Su Sun
Monday M Mo Mon
Tuesday T Tu Tue
Wednesday W We Wed
Thursday R Th Thu
Friday F Fr Fri
Saturday S Sa Sat


Durations are not commonly used in the content of this site, but they are included here for completeness.

This is probably best explained and understood using several examples:

In general, P<date>T<time>, where <date> and <time> contain “atoms” according to the specified time unit with a preceding count. Atoms are ordered with the largest unit first, and atoms without any value are omitted.


Intervals represent ranges of that are anchored to a specific date and/or time (either at the start, at the end, or both). If either the start or the end is not a date/time, then a duration is used instead.

The specification defines intervals using the following format options:

  1. <start>/<end> - anchored with date/time on both sides,
  2. <start>/<duration> - anchored with a start date/time and duration following, or
  3. <duration>/<end> - anchored with an end date/time and duration preceding.

The first format is almost exclusively used in the content on this site. This format permits the omission of higher-ordered elements (i.e., those with larger units) that are identical between the start and end. For example: