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Unix time counts elapsed seconds from 00:00:00 UTC on January 1, 1970. The same timestamp identifies one instant everywhere; local timezones only change how that instant is displayed.
Many backend systems store whole seconds, while JavaScript dates use milliseconds. A contemporary seconds value usually has 10 digits and a milliseconds value 13. Auto-detection is convenient, but the explicit unit selector should be used for unusual historical or far-future values.
Enter epoch seconds or milliseconds to see local, UTC, ISO 8601, relative, weekday, and timezone details. In the reverse direction, choose whether the date and time should be interpreted in the browser’s local timezone, UTC, or a named IANA timezone.
Numeric instants are compact, easy to compare, and independent of display formatting. JWT claims such as iat and exp, cache expiry values, and scheduled events frequently use Unix seconds.
Signed 32-bit systems overflow second-based Unix time in January 2038. Modern JavaScript dates are not limited to 32-bit seconds, although they still have a finite supported range that this tool validates.
No. Timezone choices affect parsing of a human-entered date and formatting of the result, not the underlying instant.
Yes. Negative values represent instants before the Unix epoch, within the browser Date range.