ISO 8601 Date Converter
Parse and convert ISO 8601 dates between calendar, basic, week and ordinal forms with the Unix timestamp, plus a full ISO 8601 duration converter.
Every equivalent form
- Input recognised as
- Calendar date, extended format
- Calendar date, extended
2026-04-03T09:30:00Z- Calendar date, basic
20260403T093000Z- Week date
2026-W14-5- Ordinal date
2026-093- Date only
2026-04-03- UTC instant
2026-04-03T09:30:00.000Z- In words
- Friday, April 3, 2026
- UTC offset
- UTC+00:00
- Unix milliseconds
- 1775208600000
- In your local time
- —
ISO 8601 duration converter
Duration breakdown
1 year, 2 months, 10 days, 2 hours, 30 minutes
Years and months have no fixed length, so the totals above use the ISO 8601 averages of 365.2425 days a year and 30.436875 days a month. Anchor the duration to a real start date if you need exact calendar arithmetic.
What is the ISO 8601 Date Converter?
The ByteTools ISO 8601 Converter reads any shape the standard allows — extended dates such as 2026-04-03, basic dates such as 20260403, week dates such as 2026-W14-3, ordinal dates such as 2026-093, fractional seconds and offsets or a Z — and rewrites your value in every other form at once, alongside the Unix timestamp in seconds and milliseconds.
- Accepts extended and basic formats, week dates, ordinal dates and fractional seconds
- Outputs every equivalent form side by side with per-row copy buttons
- Unix timestamp in seconds and milliseconds, plus the weekday and UTC offset
- Specific parse errors that name the offending field and its valid range
- ISO 8601 duration parser with totals in days, hours, minutes and seconds
- Local-time rendering appears once the page is interactive, so nothing shifts on load
How to use the ISO 8601 Date Converter
- 1
Paste an ISO 8601 date or date-time, or load one of the example formats from the dropdown.
- 2
Read the equivalent calendar, basic, week, ordinal and UTC forms, each with its own copy button.
- 3
Check the Unix timestamp, the UTC offset and the value in your local time once the page loads.
- 4
Enter an ISO 8601 duration in the lower section to break it into days, hours, minutes and seconds.
- 5
Copy all of the equivalent forms, or the duration breakdown, as plain text.
About the ISO 8601 Date Converter
The ByteTools ISO 8601 Converter reads any shape the standard allows — extended dates such as 2026-04-03, basic dates such as 20260403, week dates such as 2026-W14-3, ordinal dates such as 2026-093, fractional seconds and offsets or a Z — and rewrites your value in every other form at once, alongside the Unix timestamp in seconds and milliseconds.
When something does not parse, you are told why in specific terms: which field is out of range, how many days that month has, or how many ISO weeks that year contains. That is far more useful than a generic invalid-date message when you are debugging a log line, an API payload or a CSV export that a parser has rejected.
A second section handles ISO 8601 durations such as P1Y2M10DT2H30M, breaking them into words and into totals in days, hours, minutes and seconds. Everything is parsed by hand in JavaScript and runs 100% locally in your browser, so timestamps taken from production logs are never uploaded to a server.
Frequently asked questions
What is the ISO 8601 date format?
ISO 8601 writes dates largest unit first, as YYYY-MM-DD, and joins a time with a T, as in 2026-04-03T09:30:00Z. Because the fields are fixed width and ordered, ISO strings sort correctly as plain text and cannot be misread as day-first or month-first.
What is an ISO week date?
A week date such as 2026-W14-3 means the Wednesday of ISO week 14 of 2026. ISO weeks start on Monday, and week 1 is the week holding the first Thursday of the year, which is why a date in early January can belong to the previous ISO year.
What does the Z at the end of a timestamp mean?
Z means the time is in UTC, with a zero offset — it is shorthand for Zulu time. A value with no Z and no offset is a floating local time whose meaning depends on the reader's zone, and the converter says so instead of quietly guessing one.
How do I read an ISO 8601 duration like P1Y2M10DT2H30M?
Read it left to right: P begins the duration, then come years, months, weeks and days, and everything after the T is hours, minutes and seconds. So P1Y2M10DT2H30M is one year, two months, ten days, two hours and thirty minutes.
Why are the day totals for a duration approximate?
Years and months have no fixed length, so converting them into days requires an average. The tool uses the ISO 8601 averages of 365.2425 days a year and 30.436875 days a month, and says so — anchor the duration to a real start date if you need exact calendar arithmetic.
What is an ordinal date?
An ordinal date such as 2026-093 gives the year and the day number within it, counting from 001 on 1 January. It turns up in aviation, science and mainframe data, and the converter shows it alongside every other form of the same day.
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