ISO 8601 Date Formatter

The ISO 8601 Date Formatter converts any date and time between the formats developers and writers actually use every day: ISO 8601 (extended and basic), RFC 2822 email dates, RFC 3339, the HTTP/GMT header format, Unix timestamps in seconds and milliseconds, ISO week and ordinal dates, and friendly locale styles. A color-coded anatomy diagram pulls the ISO 8601 string apart so you can see exactly what each digit means, and every result copies with a single click. Everything runs live in your browser, so it is fast and private.

What Is ISO 8601?

ISO 8601 is the international standard for writing dates and times, published by the International Organization for Standardization. Its defining idea is to order each field from the largest unit to the smallest — year, then month, then day, then hour, minute and second — so that dates sort correctly even when treated as plain text. The familiar extended form looks like this:

2026-06-29T14:30:00+05:00

Because it is unambiguous and language-independent, ISO 8601 is the default date format in JSON, most web APIs, SQL databases, log files, and the JavaScript Date.prototype.toISOString() method.

The Anatomy of an ISO 8601 Date

Each part of the string has a fixed width and meaning. Reading 2026-06-29T14:30:00+05:00 left to right:

ISO 8601 vs RFC 2822 vs Unix Time

• ISO 8601 (2026-06-29T14:30:00+05:00) is the modern, machine-readable standard. Use it for storage, APIs, and anywhere dates need to sort or compare reliably.
• RFC 2822 (Mon, 29 Jun 2026 14:30:00 +0500) is the older human-readable format from email. You will see it in email Date: headers and many RSS and Atom feeds.
• HTTP date (Mon, 29 Jun 2026 09:30:00 GMT) is a fixed GMT variant required by HTTP headers such as Last-Modified, Expires, and Date.
• Unix timestamp (1782714600) counts seconds since 1970-01-01 UTC. It is compact and always in UTC, which makes it ideal for measuring durations and storing instants.

What Does the “Z” (Zulu Time) Mean?

A trailing Z stands for Zulu time, the military and aviation name for UTC. It is exactly equivalent to an offset of +00:00. So 2026-06-29T09:00:00Z and 2026-06-29T09:00:00+00:00 describe the very same instant. When you change the UTC offset in this tool, the “RFC 3339 / UTC (Z)” card recalculates the matching moment in UTC for you.

ISO Week Dates and Ordinal Dates

ISO 8601 also defines two alternative ways to name a day:

• Week date — for example 2026-W27-1. This is the ISO year, the week number (01–53), and the weekday (1 = Monday … 7 = Sunday). ISO weeks always begin on Monday, and week 1 is the week that contains the year's first Thursday. Around the New Year the ISO year can therefore differ from the calendar year.
• Ordinal date — for example 2026-180. This is the year plus the day-of-year from 001 to 366. It is widely used in aviation, astronomy, and legacy mainframe systems.

How to Use the ISO 8601 Date Formatter

1. Pick a date and time: Use the date and time pickers, or click a quick example such as the Unix Epoch or the current moment.
2. Choose a UTC offset: Select the offset your time is in — for example UTC+00:00, UTC-05:00 (EST), or UTC+05:30 (India).
3. Read the formats: Every format updates instantly. The anatomy diagram shows how the ISO string is built, and the relative-time line tells you how far the instant is from now.
4. Copy what you need: Click the copy button on any card, or “Copy ISO 8601” under the diagram.

Frequently Asked Questions

What is the ISO 8601 date format?

ISO 8601 is the international standard for representing dates and times. Its extended form looks like 2026-06-29T14:30:00+05:00, written from the largest unit to the smallest: year, month, day, a T separator, then hour, minute, second and the UTC offset. Because the parts are ordered big-to-small, ISO 8601 dates sort correctly as plain text.

What does the Z mean in an ISO 8601 date?

The trailing Z stands for Zulu time, which means UTC with a zero offset. So 2026-06-29T09:00:00Z is exactly the same instant as 2026-06-29T09:00:00+00:00. A date ending in Z is already expressed in UTC and needs no further offset adjustment.

What is the difference between ISO 8601 and RFC 2822?

ISO 8601 (for example 2026-06-29T14:30:00+05:00) is the machine-friendly standard used in JSON, APIs and databases. RFC 2822 (for example Mon, 29 Jun 2026 14:30:00 +0500) is the older human-readable format used in email Date: headers, with the weekday and month spelled out. They describe the same instant in different layouts.

What is a Unix timestamp?

A Unix timestamp is the number of seconds that have elapsed since 1970-01-01 00:00:00 UTC, known as the Unix epoch. It is always measured in UTC, so it is unambiguous worldwide. JavaScript and many APIs use the millisecond version, which is the same value multiplied by 1000.

What is an ISO week date?

An ISO week date such as 2026-W27-1 gives the ISO year, the week number from 01 to 53, and the weekday from 1 (Monday) to 7 (Sunday). ISO weeks always start on Monday, and week 1 is the week containing the year's first Thursday, so the ISO year can differ from the calendar year around New Year.

Does this tool send my dates to a server?

No. The conversion runs entirely in your browser with JavaScript, updating live as you change the date, time or offset. Nothing you type is uploaded, which makes the tool fast and private.

Additional Resources

• ISO 8601 - Wikipedia
• Unix Time - Wikipedia