ISO 8601 Formatter & Duration Builder
Parse timestamps, calendar dates, week dates (YYYY-Www-D), or ordinal dates (YYYY-DDD) into every ISO 8601 representation, and build or decode P...T... durations.
Private by architecture:
All processing is 100% client-side memory. Your data never leaves this browser tab.
Date / Timestamp Input
| Format Profile | Output Value | Action |
|---|
ISO 8601 Duration (P...T...) Builder & Parser
- Normalized
- P2DT6H30M
- Plain English
- 2 days, 6 hours, 30 minutes
- Total seconds (approx)
- 196200 s
About This Tool
Parses ISO 8601 strings, RFC 2822 dates, Unix epoch seconds/milliseconds, week dates (YYYY-Www-D), or ordinal dates (YYYY-DDD) and outputs every standard ISO 8601 representation side by side.
Includes an interactive ISO 8601 Duration (P[nY][nM][nW][nD]T[nH][nM][nS]) builder and parser with timezone offset conversion powered by the browser Intl API.
Key Features
- All ISO 8601 date profiles: Generates extended UTC (Z), millisecond UTC, IANA timezone offset, RFC 3339 space-separated, basic compact (YYYYMMDDTHHmmssZ), ISO week date (YYYY-Www-D), and ordinal day-of-year (YYYY-DDD).
- Bidirectional week & ordinal parsing: Paste a week date like 2026-W17-1 or ordinal date like 2026-110 to convert it back to a calendar date and Unix epoch.
- Duration builder & parser: Construct or decode P...T... duration strings (such as P2DT6H30M) with plain-English breakdown and approximate total seconds.
- IANA timezone selector: Compute exact UTC offsets (including DST transitions) for any IANA timezone via Intl.DateTimeFormat.
Frequently Asked Questions
How is an ISO 8601 week date (YYYY-Www-D) calculated?
ISO weeks start on Monday (day 1) and end on Sunday (day 7). Week 01 of any year is the week containing the first Thursday of January (or equivalently, January 4th). Because of this rule, December 31 or January 1 can belong to the adjacent ISO week-numbering year.
Why does ISO 8601 duration use M for both months and minutes?
In an ISO 8601 duration string like P1Y2M3DT4H5M6S, designators before the T separator apply to calendar units (Y = years, M = months, W = weeks, D = days), while designators after T apply to time units (H = hours, M = minutes, S = seconds).
What is the difference between ISO 8601 extended and basic format?
Extended format separates components with hyphens and colons (2026-04-20T14:30:00Z), whereas basic compact format omits separators (20260420T143000Z) for URL-safe filenames and compact wire headers.
