Unix timestamp converter
Convert Unix seconds or milliseconds to a UTC date, or an ISO date with an explicit timezone to Unix time. Check units without guessing.
Free to use · No sign-up · Inputs stay in your browser
Give the time a unit
The example represents midnight UTC on 1 January 2024. Choose the input format explicitly so seconds and milliseconds cannot be confused.
Current time uses your device clock when clicked. Results stay fixed while you inspect them.
The same instant in UTC
Conversion complete. UTC output does not depend on your device timezone.
Supports UTC years 0000–9999 and millisecond precision. Leap seconds, named zones and ambiguous local dates are not supported. Unix time counts from 1970-01-01T00:00:00Z.
Practice tracing a unit mismatch
An API promises Unix seconds but a consumer passes the number directly to new Date(value). Which boundary should you inspect first?
Check the reasoning
Inspect the seconds-to-milliseconds conversion at the consumer boundary. JavaScript’s numeric Date constructor uses milliseconds. Test one known instant and make the unit explicit; a formatted date alone cannot tell you what the producer intended.
This is an original open example, not a scored drill. Close the tool before taking a diagnostic or an unassisted practice session.
About 14 minutes, no account needed. A free account adds a daily practice queue; paid plans add more practice and the full library.
How to use the result
Choose Unix seconds, milliseconds or an ISO date. Unix inputs must be whole numbers. ISO input requires seconds and Z or a numeric offset, with up to three fractional digits. Output is UTC; years 0000–9999 are supported. Leap seconds and named timezone rules are outside this tool’s scope.
1704067200 Unix seconds is 2024-01-01T00:00:00.000Z. The same number in milliseconds is 1970-01-20T17:21:07.200Z. The unit changes the result, so the converter never guesses from the number of digits.
These utilities and open examples do not contribute to your diagnostic score or practice history.
MDN: Date.parse and date formats