Why is ISO 8601 the standard?

Because it sorts as text. Fields run largest to smallest, so a plain string comparison orders dates correctly, which no other common format manages.

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ISO 8601 Date Converter

ISO 8601 formatting in UTC and with an offset, plus the week and ordinal forms. Ordering fields largest first is why ISO strings sort chronologically as plain text.

Also called: iso 8601 formatter, timezone offset converter.

ISO 8601, in UTC

2026-08-18T09:00:00Z

2026-08-18T09:00:00Z. In your local offset that is 2026-08-18T14:30:00+05:30, and the Unix timestamp is 1,787,043,600.

ISO 8601 with the offset

2026-08-18T14:30:00+05:30

Unix timestamp

1,787,043,600

ISO week date

2026-W34-2

ISO ordinal date

2026-230

How this is calculated

Method and background

How this is calculated

ISO 8601 writes year, month, day, hour, minute, second in descending order of significance, which means lexical sorting and chronological sorting are the same operation. That single property is why it is the interchange format everywhere. The offset is part of the timestamp rather than metadata, so an ISO string with an offset is unambiguous in a way a bare local time is not.

ISO 8601 orders fields largest first, which makes the text sort chronologically

offset: Hours from UTC

Worked examples

Each of these is asserted on every build. If a change to the engine ever moved one of these answers, the build would fail before the page could print it.

India offset to UTC

Date: 2026-08-18
Hour: 14
Minute: 30
Time zone offset from UTC: 5.5

ISO 8601, in UTC2026-08-18T09:00:00Z

14:30 less five and a half hours

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a zero offset is already UTC

Date: 2026-08-18
Hour: 14
Minute: 30
Time zone offset from UTC: 0

ISO 8601, in UTC2026-08-18T14:30:00Z

boundary

Open this example

Method and limits

What it assumes

A fixed offset rather than a named zone, so daylight saving is yours to apply.

What it deliberately does not model

A named time zone carries its own daylight-saving history, which an offset does not.
Offsets of 30 and 45 minutes exist and are supported through the fractional input.

Formula version 1.0.0 · definition 1.0.0 · United States · Report a problem with this calculator

Frequently asked questions

Why is ISO 8601 the standard?: Because it sorts as text. Fields run largest to smallest, so a plain string comparison orders dates correctly, which no other common format manages.