ISO 8601 Date Converter & Validator
An ISO 8601 date follows YYYY-MM-DDTHH:mm:ss.sssZ. This converter validates the input strictly, normalizes basic / extended / ordinal / week-date variants, and emits all equivalent forms — including the Unix epoch and an RFC 3339 profile.
Quick Conversion
Formula: ms = ISO seconds × 1000
ISO 8601 variant gallery
Same instant, every ISO 8601 form
| Variant | Representation |
|---|---|
| Extended UTC | 2024-05-30T01:00:00Z |
| Extended +offset | 2024-05-30T06:30:00+05:30 |
| Basic UTC | 20240530T010000Z |
| Basic +offset | 20240530T063000+0530 |
| Ordinal date | 2024-151T01:00:00Z |
| Week date | 2024-W22-4T01:00:00Z |
| Date only | 2024-05-30 |
| Time only | 01:00:00 |
| With ms | 2024-05-30T01:00:00.000Z |
| With ns | 2024-05-30T01:00:00.000000000Z |
Need the strict RFC 3339 profile? RFC 3339 converter.
ISO 8601 grammar (ABNF-ish)
date-time = full-date "T" full-time
full-date = year "-" month "-" day ; or yearmoday
full-time = HH ":" MM ":" SS [.frac] tz
tz = "Z" / ("+" / "-") HH ":" MMWorked: 2024-05-30T01:00:00.000Z → year=2024, month=05, day=30, HH=01, MM=00, SS=00, frac=.000, tz=Z.
How to validate and rewrite an ISO 8601 datetime
- 1Paste any ISO 8601 form (basic, extended, ordinal or week-date) into the input. Trailing whitespace is ignored.
- 2The green check or red banner confirms validity. Out-of-range months/days/seconds are flagged explicitly.
- 3Scan the eight equivalent forms in the right rail — copy whichever your downstream system needs.
- 4Hover the colored SVG legend to see which substring maps to which field.
- 5Save the snapshot to local history; later you can repopulate the field with one click.
From ISO 2014 to ISO 8601-2:2019 — a brief history
In 2026 a backend engineer handling cross-border audit logs needs to validate that every created_at string in their JSON payload is strict ISO 8601, not the lossy "5/30/24 1:00 AM EST" their CSV vendor sends. That single check shaved a CI failure off the deploy. This converter is the tool that surfaces the validation.
ISO 2014 (1971) was the first international date standard — it gave us the YYYY-MM-DD ordering that everyone now takes for granted. ISO 2015 (1971) added week numbering. The two were merged and extended into ISO 8601 in 1988. The first revision (8601:2000) added the T separator and the Z suffix; the second (8601:2004) standardised time intervals.
ISO 8601-1:2019 is the current calendar/clock revision. ISO 8601-2:2019 added extensions: negative years for prehistoric dates, year > 9999 for far-future planning, and named geometric durations like P1Y2M10DT2H30M. Most JSON APIs target only the "basic core" profile that 8601-1 defines.
Internet engineering built its own subset. In 2002 Chris Newman and Graham Klyne published RFC 3339, banning week and ordinal dates, mandating the T separator, and requiring either Z or a zone offset. The result is unambiguous, easy to grep for, and sortable as a string. Every modern REST API should emit RFC 3339.
In databases, ISO 8601 has won. PostgreSQL parses ISO timestamps natively; 2024-05-30T01:00:00Z::timestamptz Just Works. SQL Server, MySQL, BigQuery, Snowflake — all accept ISO literals. Store as the native TIMESTAMP type for arithmetic, or as a VARCHAR for archival.
The format is also forensic-friendly. Because extended ISO 8601 sorts lexicographically (string compare = chronological compare), log lines can be `awk -F'T' '$0 > "2024-05-30T00"'` without parsing. That single property is why every modern logging stack — fluentd, Vector, OpenTelemetry — emits ISO 8601 by default.
The summary: pick extended ISO 8601 with Z (UTC) as your wire format, keep ms or µs precision, validate ranges at ingest, and use a typed library to manipulate — never string-template. This tool exists to make the validate-at-ingest step a one-second copy-paste.
Trusted by engineers, DBAs and analysts
“Reformatting between basic and extended ISO 8601 used to mean a sed pipe. Now one click. Bonus: catches my off-by-one weekdays.”
“The validator caught a stray '2024-02-30' in my test fixture. Saved me a wasted CI run.”
“Ordinal date support is surprisingly useful for our partition keys. Most converters omit it.”
“Week-date conversion (ISO-W22-4) is exactly what I need to validate weekly KPI reports.”
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