ISO 8601 is the international standard covering the exchange of date- and time-related data, establishing an unambiguous, lexicographically sortable date format.
ISO 8601 (Data elements and interchange formats – Information interchange – Representation of dates and times) is the globally recognized standard published by the International Organization for Standardization (ISO) establishing an unambiguous, cross-cultural numerical representation of dates, times, time intervals, and timezone offsets.
Convert, format, and validate ISO 8601 strings, RFC 3339 dates, and Unix timestamps with our free Timestamp Converter tool.
A standard extended format ISO 8601 date-time string is composed of distinct hierarchical segments ordered from largest to smallest temporal unit:
2024-05-14T01:00:00.000Z
└──┬───┘└┬┘└┬┘└┬┘└┬┘└┬┘└┬──┘│
│ │ │ │ │ │ │ └── Zulu / UTC indicator (+00:00)
│ │ │ │ │ │ └────── Milliseconds (0-999)
│ │ │ │ │ └───────── Seconds (00-59)
│ │ │ │ └──────────── Minutes (00-59)
│ │ │ └─────────────── Hours (00-23 in 24-hour format)
│ │ │
│ │ └────────────────── Time separator ('T')
│ │
│ └───────────────────── Month (01-12) & Day (01-31)
└─────────────────────────── 4-digit Gregorian Year
While often used interchangeably in software development, RFC 3339 is a strict internet profile of ISO 8601 designed specifically for HTTP headers, JSON APIs, and cryptographic certificates:
| Feature | ISO 8601 (ISO 8601-1:2019) | RFC 3339 |
|---|---|---|
| Primary Scope | Broad international specification | Web, Internet protocols, JSON REST APIs |
| Date/Time Separator | T delimiter standard |
Accepts T or space ( ) |
| Timezone Offset | Allows Z, +HH:MM, +HHMM, or +HH |
Requires Z or +HH:MM |
| Sub-second Fractions | Unlimited precision with comma or dot | Unlimited precision with dot delimiter (.) |
| Two-Digit Years | Allowed in older variants | Strictly forbidden (4-digit minimum) |
| Ordinal & Week Dates | Supported (2024-W20-2, 2024-135) |
Not supported (Calendar dates only) |
Z Suffix: Indicates Coordinated Universal Time (UTC), often called Zulu time (military phonetic alphabet).+05:30 for Indian Standard Time), while negative offsets indicate time behind UTC (e.g. -04:00 for Eastern Daylight Time).2024-05-14T06:30:00+05:30 and 2024-05-14T01:00:00Z refer to the exact same physical instant in time.A-Z) yields precise chronological ordering without parsing.05/06/2024 means May 6 in the United States but June 5 in the United Kingdom and Europe. ISO 8601 (2024-05-06) is universally unambiguous.JSON.stringify() in ECMAScript serializes Date objects into ISO 8601 strings automatically via Date.prototype.toISOString().Free, browser-based utilities to test, generate, and inspect ISO 8601 & RFC 3339 Date-Time Standard payloads directly.
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