The Unix epoch
0 seconds identifies 1970-01-01T00:00:00.000Z. The same instant can display as the previous calendar date in a time zone west of UTC.
0Unix seconds (exact decimal)
0Unix milliseconds
In UTC
Thursday, January 1, 1970 AD at 00:00:00.000 GMT+00:00
Whole seconds rounded down: 0. A negative fractional timestamp is before 1970; −0.001 seconds is the final millisecond of 1969. Leap seconds are excluded.
Calculations run in your browser. Dates and settings are not uploaded by this tool.
How to use the Unix Timestamp Converter
- 01
Choose Unix timestamp or ISO date-time as the source. Explicitly choose seconds or milliseconds for timestamp input.
- 02
For a date-time, enter YYYY-MM-DDTHH:MM:SS with Z or a known numeric UTC offset; up to three fractional digits are accepted.
- 03
Choose an IANA time zone for the local display. It changes the displayed calendar time, not the underlying instant.
- 04
Review exact decimal seconds, integer milliseconds, and the normalized UTC string. Use the current-instant action or copy the full conversion.
Examples
A negative fractional timestamp
−0.001 seconds is −1 millisecond, or 1969-12-31T23:59:59.999Z. Its whole seconds rounded down is −1, not 0.
An offset identifies the same instant
1970-01-01T01:00:00+01:00 converts to Unix timestamp 0. The written wall time differs from UTC by one hour, but the explicit offset resolves the instant.
Seconds and milliseconds must be distinguished
The tool never infers units from digit count. A value of 1000 means 1,000 seconds in seconds mode and only one second in milliseconds mode. Seconds accept at most three decimal places, while milliseconds require an integer. Decimal input is processed at millisecond precision so far-future boundary values do not lose a millisecond to floating-point multiplication.
Require an offset when converting a date-time
A wall-clock string without a time zone can identify different instants in different locations. This parser therefore requires Z or a numeric offset and rejects invalid calendar dates instead of normalizing them into another month. It also rejects −00:00, whose RFC convention means the local offset is unknown. Use the Time Zone Converter when you have a location and need daylight-saving ambiguity checked.
Precision, leap seconds, and range
The result uses the JavaScript time scale: milliseconds relative to the Unix epoch, without representing UTC leap seconds. Second 60 is rejected. Supported instants run from the first millisecond of year 0001 through the final millisecond of year 9999 in UTC. IANA display conversions depend on the time-zone data installed in your browser or operating system.
What to know
- Supported explicit offsets are from −14:00 through +14:00. Fractional precision is limited to milliseconds.
Common questions
Does changing the display zone change the timestamp?
No. The zone changes only the readable calendar time. The UTC string and Unix values continue to identify the same instant.
Why is an ISO date without seconds rejected?
This converter uses a deliberately explicit input form with hours, minutes, seconds, and a known UTC offset. Supply the missing fields so the result can be interpreted consistently.
Are fractional seconds rounded?
No. Up to three decimal digits are accepted exactly; extra digits are rejected. The separate whole-seconds figure uses floor rounding, including for negative timestamps.