Date and time converter
Convert between ISO 8601, RFC 3339, RFC 7231, Unix seconds/milliseconds, date-only or time-only, relative time, weekday and day of year, in any IANA time zone.
Runs in your browserEvery computation happens in your browser — your data never leaves this device.
All formats
Inputs without a time zone are read in the selected time zone; the list comes from the browser Intl.supportedValuesOf('timeZone').
What this tool does
- Turn a timestamp from logs or an API payload (1700000000, 1700000000000) into a readable date, or go the other way and put a timestamp into a request parameter.
- Debug time-zone problems: the same instant is shown as ISO, RFC 3339 and UTC offset in UTC and Asia/Shanghai, so the difference is obvious at a glance.
- Produce RFC 7231 (GMT) dates for HTTP caching or Last-Modified headers.
- Grab derived values — weekday, day of year, relative time ("3 hours ago") — for copywriting or data checks.
Example
Input
1700000000 (time zone UTC)
Output
ISO 8601 (UTC): 2023-11-14T22:13:20.000Z RFC 3339: 2023-11-14T22:13:20+00:00 RFC 7231: Tue, 14 Nov 2023 22:13:20 GMT Unix seconds: 1700000000 Unix milliseconds: 1700000000000 Date: 2023-11-14 Time: 22:13:20 Weekday: 星期二 (Tuesday, shown localised) Day of year: 318 UTC offset: +00:00
Up to ten digits is read as Unix seconds and eleven to thirteen as milliseconds; switch to Asia/Shanghai and the RFC 3339 value becomes 2023-11-15T06:13:20+08:00. The weekday name follows the page language.
Frequently asked questions
Which time zone is used for input without one?
The one selected in the dropdown. With Asia/Shanghai selected, typing 2026-10-10 20:00 means 8pm in UTC+8, which is 12:00 UTC. Select UTC to treat it as the zero offset instead.
How are timestamps told apart by length?
For a plain number (optionally signed), up to ten digits after the sign is Unix seconds, eleven to thirteen is milliseconds, and anything longer is rejected. Ten digits covers the familiar 2001–2038 range, so there is no ambiguity.
What is the difference between RFC 3339 and ISO 8601?
ISO 8601 is the larger family of standards and RFC 3339 is the subset aimed at internet protocols. The ISO value here always ends in Z for UTC (the toISOString form), while RFC 3339 carries the offset of your selected zone, such as +08:00.
Why does the relative time say "just now"?
Relative time is measured against the current instant, and the value you entered is close to now. It rounds by range: within 45 seconds is "just now", within 90 seconds is "1 minute ago", then minutes, hours, days, months and years.
Does it get daylight-saving transitions wrong?
No. The conversion reads the real offset of the target zone at that instant through Intl.DateTimeFormat and re-checks with a second pass when the offset may change. Wall-clock times that do not exist or occur twice on a transition day, such as in America/New_York, are reported as invalid input.
Keywords：datetimedatetime日期时间时区timezoneiso 8601rfc 3339rfc 7231day of year相对时间日期时间转换