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Glossary Data & Encoding

ISO 8601

ISO 8601 is the international standard for writing dates and times unambiguously, in the order year, month, day, such as 2026-10-03T14:30:05Z.

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In more detail

Because the biggest unit comes first, ISO dates sort correctly as plain text. The standard also defines week dates (2026-W40-6, which is Saturday of week 40), durations (P1Y2M3D) and intervals. See the Date & Time Formats Cheat Sheet.

Try these tools

Week Number Calculator

Find the ISO 8601 week number of any date, the US week number, the day of the year and quarter.

Day of the Week Calculator

Find the day of the week for any historical or future date.

See also

  • Glossary UTC
    UTC is the global reference time standard from which all time zones are defined as offsets.
  • Glossary Unix timestamp
    A Unix timestamp is the number of seconds since 00:00:00 UTC on 1 January 1970, the "Unix epoch".
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