ISO 8601 Date Converter
Convert any date to every ISO 8601 variant — extended, basic, week notation, and ordinal. Also parse ISO 8601 strings to readable dates.
→ / ← to move · ↑↓ to adjust
→ / ← to move · ↑↓ to adjust
What Is ISO 8601?
ISO 8601 is the international standard for representing dates and times, first published in 1988 and most recently revised in 2019. Its defining feature is a fixed structure that eliminates ambiguity: the largest unit (year) always comes first, followed by month, then day. This means ISO 8601 dates sort lexicographically in the same order as chronologically — 2026-01-15 sorts before 2026-02-03 alphabetically, and also earlier in time.
ISO 8601 is the format returned by JavaScript's Date.prototype.toISOString(), used by most REST APIs, required by HTML <input type="datetime-local">, stored internally by PostgreSQL's timestamp type, and expected by many logging frameworks. Understanding its variants helps you handle dates correctly across systems.
ISO 8601 Variants
Date only: YYYY-MM-DD — the most common form. 2026-02-25 means February 25, 2026. Unambiguous internationally; contrast with 02/25/2026 (US) or 25/02/2026 (European), which mean the same date but cannot be parsed without knowing the local convention.
Basic vs Extended: The extended format uses hyphens and colons as separators: 2026-02-25T14:30:00. The basic format omits separators: 20260225T143000. Extended is preferred for human readability; basic is sometimes used in compact storage or filenames.
UTC (Z suffix): Appending Z (Zulu time) explicitly declares UTC: 2026-02-25T14:30:00Z. Without a suffix or offset, the timezone is technically unspecified.
Timezone offset: Replace Z with ±HH:MM: 2026-02-25T09:30:00-05:00 is the same instant as 2026-02-25T14:30:00Z (UTC-5, Eastern Standard Time).
Week notation: YYYY-Www-D — year, ISO week number (01–53), and day of week (1=Monday, 7=Sunday). 2026-W09-3 is Wednesday of the 9th ISO week of 2026. ISO weeks always start on Monday; Week 1 is the week containing the year's first Thursday.
Ordinal date: YYYY-DDD — year and day-of-year (001–366). 2026-056 is the 56th day of 2026 (February 25).
Parsing ISO 8601 in Code
JavaScript: new Date('2026-02-25T14:30:00Z') parses ISO 8601 strings natively. Note: new Date('2026-02-25') (date only, no time) is parsed as UTC midnight, while new Date('2026-02-25T00:00:00') (with time, no offset) is parsed as local midnight — a frequent source of off-by-one-day bugs.
Python: datetime.fromisoformat('2026-02-25T14:30:00+00:00') (Python 3.7+). For full ISO 8601 support including Z: datetime.strptime(s, '%Y-%m-%dT%H:%M:%SZ'), or use the dateutil library for robust parsing.
SQL: ISO 8601 strings can be cast directly in most databases: CAST('2026-02-25' AS DATE) in PostgreSQL, MySQL, and SQL Server.
Frequently Asked Questions
What is ISO 8601?
ISO 8601 is an international standard for representing dates and times. The standard format places the largest unit first: year-month-day (YYYY-MM-DD). This makes dates sort chronologically when sorted alphabetically, eliminating ambiguity across locales.
What does the T mean in an ISO 8601 datetime?
The T separates the date portion from the time portion: 2026-02-25T14:30:00. It is required in the extended format. Some systems accept a space as an alternative separator, but T is the standard.
What does the Z mean in an ISO 8601 datetime?
Z stands for Zulu time (UTC). 2026-02-25T14:30:00Z means 2:30 PM UTC on February 25, 2026. It is equivalent to +00:00 as a timezone offset.
What is ISO 8601 week notation?
YYYY-Www-D: year, ISO week number (01–53), day of week (1=Monday, 7=Sunday). Week 1 is defined as the week containing the year's first Thursday. ISO weeks always start on Monday.
What is an ISO 8601 ordinal date?
YYYY-DDD: year and day number within that year (001–365, or 366 in a leap year). 2026-056 = February 25, 2026 (the 56th day of the year).