ISO 8601-1-2019 PDF

Full title and description

ISO 8601-1:2019 — Date and time — Representations for information interchange — Part 1: Basic rules. This international standard defines unambiguous character-string representations for Gregorian calendar dates, 24‑hour clock times, composite date‑time elements and UTC‑referenced time shifts for use in information interchange.

Abstract

This part of ISO 8601 specifies the basic rules for expressing calendar dates, ordinal dates, week dates, times of day (24‑hour clock), combined date‑time strings, time shifts (offsets) and related composite elements as character strings intended for reliable information interchange. It excludes non‑Gregorian calendars, clocks not using the 24‑hour convention and does not mandate character encoding for the resulting strings. The publication includes definitions, symbols, fundamental principles and rules for reduced precision, separators, leading zeros and the representation of intervals and durations.

General information

• Status: Published (International Standard; confirmed current in ISO review 2024).
• Publication date: February 2019 (Edition 1, 2019-02).
• Publisher: International Organization for Standardization (ISO).
• ICS / categories: 01.140.30 (Documents in administration, commerce and industry).
• Edition / version: Edition 1 (2019). Amended by ISO 8601-1:2019/Amd 1:2022 (technical corrections).
• Number of pages: 38 (core ISO publication; combined national/adopted versions with amendment may show larger page counts where amendment text is integrated).

Scope

Defines the basic rules for representing dates and times for information interchange: calendar date (YYYY-MM-DD and variants), ordinal date (YYYY-DDD), week date (YYYY-Www-D), local time (24‑hour clock), UTC time with time‑shift designators, composite date‑time strings separated by the letter "T", durations, time intervals and recurring intervals (in conjunction with Part 2 for extended repeat rules). The document sets out symbols, terms, permitted separators, rules for reduced precision and handling of leap seconds and end‑of‑day representations. It explicitly excludes non‑Gregorian calendar systems and non‑24‑hour clocks.

Key topics and requirements

• Canonical and alternative date representations: calendar, ordinal and week date forms.
• 24‑hour clock time formats, fractional seconds and rules for reduced precision.
• Time‑shift (offset) notation relative to Coordinated Universal Time (UTC) and rules for combining date and time with the "T" designator.
• Rules for leading zeros, separators (basic vs extended formats), permitted omitted components and expansion behavior.
• Representation of durations and time intervals; guidance on recurring intervals (with extended rules referenced in Part 2).
• Clarifications on ambiguous terms (e.g., handling of "midnight") and treatment of leap seconds and the 24:00 end‑of‑day notation (technical corrections added by amendment).

Typical use and users

Adopted widely by software engineers, API designers, database architects, systems integrators, archivists and standards authors where unambiguous date/time interchange is required. Typical uses include timestamp formats for data exchange, logging, event ordering, metadata in bibliographic systems, machine‑readable data feeds, configuration files and any interoperability scenario where a consistent textual representation of date/time is required.

Related standards

ISO 8601-2:2019 (Extensions) — provides extended formats and additional rules; ISO 8601-1:2019/Amd 1:2022 (technical corrections). Predecessor: ISO 8601:2004. Related Internet and library profiles include RFC 3339 (Internet profile of ISO 8601), W3C date/time usages (XML Schema dateTime) and EDTF (Extended Date/Time Format) which influenced some extended representations.

Keywords

ISO 8601, date format, time format, UTC, timestamp, calendar date, week date, ordinal date, duration, interval, time offset, interchange, 24‑hour clock.

FAQ

Q: What is this standard?

A: ISO 8601-1:2019 is Part 1 of the ISO 8601 family; it defines the basic rules for representing dates and times as character strings for information interchange (calendar dates, 24‑hour clock times, combined date‑time, time shifts, durations and intervals).

Q: What does it cover?

A: It covers canonical and permitted alternative string formats for Gregorian calendar dates (calendar, ordinal, week), times on the 24‑hour clock (including fractional seconds), time‑shift/offset notation relative to UTC, rules for combining elements, reduced‑precision forms, durations and intervals, and normative definitions and symbols used in these representations. Non‑Gregorian calendars and non‑24‑hour clocks are excluded.

Q: Who typically uses it?

A: Developers, database and API designers, system integrators, archivists, metadata specialists and anyone needing a standard, unambiguous textual representation of date/time for exchange between systems.

Q: Is it current or superseded?

A: ISO 8601-1:2019 is the current Part 1 publication (Edition 1, 2019). It was amended (ISO 8601-1:2019/Amd 1:2022) for technical corrections; it replaced ISO 8601:2004. The ISO entry for the standard was reviewed and confirmed in 2024.

Q: Is it part of a series?

A: Yes — it is Part 1 (basic rules) of the ISO 8601 series. Part 2 (ISO 8601-2:2019) covers extensions and additional representations; national adoptions and amendments exist that incorporate the amendment text into local publications.

Q: What are the key keywords?

A: Date, time, timestamp, UTC, ISO 8601, calendar date, week date, ordinal date, duration, interval, interchange.