Convert Unix seconds or milliseconds to UTC and browser local time, or turn an ISO date with a timezone into an exact Unix timestamp. Everything happens on your device.
Your dates and timestamps never leave your browser. Conversion needs no uploads, external API, account or saved input history. Explicit units and required timezone offsets avoid silent guesses about what your input means.
A Unix timestamp measures time relative to 1970-01-01T00:00:00Z. Seconds and milliseconds are different units for the same instant; one second is 1,000 milliseconds. Negative values represent instants before the epoch. This tool follows JavaScript Date’s Unix-style timeline without leap seconds.
No. Choose the input unit explicitly. Seconds allow up to three decimal places and milliseconds must be whole integers. The output always includes both units, preserving the instant to one millisecond. Scientific notation, grouping separators, microseconds and nanoseconds are not accepted.
Use YYYY-MM-DDTHH:mm:ss with optional one to three fractional digits, followed by uppercase Z or a numeric ±HH:mm offset. For example, 2024-01-01T05:30:00+05:30. A timezone and seconds are required. Date-only strings, timezone names, ambiguous local times, leap seconds, 24:00 and impossible dates are rejected. Numeric offsets are limited to ±23:59; this does not validate an offset against a real-world timezone.
They display the same instant using different timezone conventions. The UTC ISO result is deterministic. The local display depends on the browser’s timezone, locale and timezone database, including historical or daylight-saving rules. Its human-readable format can omit milliseconds; use UTC and Unix outputs for exact precision. Local time is a display, not an input format.
Supported instants are UTC years 0000 through 9999, from 0000-01-01T00:00:00.000Z to 9999-12-31T23:59:59.999Z, using JavaScript’s proleptic Gregorian calendar. Year 0000 is accepted. Offsets that move an otherwise valid input outside that UTC range are rejected. This is a deliberate subset of JavaScript Date’s broader range.
Use current time takes one snapshot of your device clock and converts it. It does not contact a time server or continuously tick, and an incorrect device clock gives an incorrect current time. Inputs and reports are not stored by this tool. Clear keeps your direction and unit settings.
