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About this tool
Convert a date/time to ISO-8601 and other formats.
The ISO 8601 Formatter converts any date/time your browser can parse into the canonical ISO 8601 UTC string, YYYY-MM-DDTHH:mm:ss.sssZ, and shows the same instant as a Unix timestamp in seconds, a UTC string and your local time. Type something like 2026-07-20 15:30 and you get 24-character ISO output plus the epoch value, with an explicit error when the input cannot be parsed. It is for developers writing API payloads, log formats and database values that must be timezone-unambiguous.
Open ISO 8601 Formatter on AltFTool — it loads instantly in your browser.
Type or paste a moment into the single 'Date/time' field under Inputs, which opens pre-filled with 2026-07-20 15:30; anything the browser's Date parser accepts works, and text it cannot parse leaves the Result at an em dash with the caption 'Enter a valid date/time'
There is no output-format picker and no Format button — the Result recomputes as you type and always shows the same set at once: the ISO-8601 UTC timestamp on the headline line, plus cards labelled 'Unix (s)', 'UTC' and 'Local'
Use Copy to place the Date/time you entered, the ISO-8601 Result and the Unix (s), UTC and Local rows on the clipboard, Download to save that text as iso-8601-formatter.txt, or Reset to put the field back to its default
Shows ISO 8601 UTC, Unix seconds, the UTC string and your local time together, so you can see the offset between them rather than converting twice.
Parses everyday forms like '2026-07-20 15:30' as well as strict ISO strings, and says plainly when a value is unparseable instead of returning a wrong date.
The ISO output is emitted in UTC with a Z suffix, which is the form that removes any ambiguity about which offset a stored timestamp was written in.
YYYY-MM-DDTHH:mm:ss.sssZ — for example 2026-07-20T10:00:00.000Z. The T separates date from time, the fractional part carries three digits of milliseconds, and the trailing Z means UTC (Zulu time), a zero offset.
Because a date typed without an offset is read as your local wall-clock time and then converted to UTC for the ISO output. In a UTC+05:30 timezone, 2026-07-20 15:30 becomes 2026-07-20T10:00:00.000Z — the same instant written in a different zone.
Enter the date and read the Unix (s) row: it is the number of whole seconds since 1 January 1970 00:00:00 UTC, floored rather than rounded. Multiply by 1000 if the system you are feeding expects milliseconds.
Because the parser could not interpret it. Ambiguous or locale-specific forms such as 20/07/2026 are unreliable across engines — write the date as YYYY-MM-DD, optionally followed by a time as HH:mm or HH:mm:ss, and it will parse consistently.