Free online tool
Unix Timestamp Converter
Convert Unix timestamps (seconds or milliseconds) to human dates, and any date back to a timestamp.
What a Unix timestamp is
A Unix timestamp is the number of seconds (or, in some systems, milliseconds) that have elapsed since 00:00:00 UTC on January 1, 1970 — a moment known as "the epoch." Because it's just an integer, it's the most compact and unambiguous way to represent a point in time, which is why virtually every database, API and log file speaks Unix time under the hood.
Seconds vs milliseconds
Traditional Unix timestamps are in seconds, but JavaScript, Java and many modern APIs use milliseconds. This converter auto-detects the unit based on magnitude: values above 1012 are treated as milliseconds, everything else as seconds. Both forms are shown when converting a date back, so you can copy whichever your system expects.
+Is Unix time in UTC?
Yes. A Unix timestamp is timezone-independent — it always represents the same instant, everywhere on Earth. Timezones only come into play when you format the timestamp as a human-readable string.
+What's the year 2038 problem?
Systems that store Unix timestamps in signed 32-bit integers overflow in January 2038. Modern systems use 64-bit integers and are unaffected.
Turning an epoch number back into a date you recognize
A Unix timestamp counts seconds elapsed since midnight UTC on January 1st, 1970. It's compact, timezone-agnostic by design, and completely unreadable to a human until something converts it back into a calendar date.
Because it's just an integer, timestamps show up in log files, database columns, API payloads, and URL query strings without any indication of their own units or timezone, which is exactly why a quick converter earns a permanent spot in most developers' toolbar rather than being something you'd compute by hand.
Seconds versus milliseconds is the first thing to check
Unix time is traditionally seconds, but JavaScript's Date.now() and most JSON APIs from web backends return milliseconds since epoch. Feed a millisecond value into a converter expecting seconds and you'll land on a date sometime in the 48000s, which is a dead giveaway you've got the units backwards — a ten-digit number is almost certainly seconds, a thirteen-digit number is almost certainly milliseconds.
Timezone display versus stored value
The timestamp itself has no timezone — it's a single point on the universal timeline — but the human-readable string you see is always rendered in some timezone, usually your browser's local one or UTC. Two people converting the exact same timestamp in different timezones will see different wall-clock times and that's expected behavior, not a bug in the converter.
The 2038 problem is closer than it sounds
Systems that store Unix time in a signed 32-bit integer will overflow on January 19, 2038, wrapping around to a negative number that decodes as a date in 1901. Most modern languages and databases have already moved to 64-bit representations, but older embedded systems, some file formats, and certain C code compiled with 32-bit time_t are still exposed, so treat dates near that boundary as worth double-checking against the underlying storage type. A related edge case shows up in date arithmetic near daylight saving transitions, where converting a timestamp to local time can land on a wall-clock hour that either repeats or doesn't exist at all, depending on the region's transition rules that year.
Leap seconds and why Unix time quietly ignores them
Unix time assumes every day has exactly 86,400 seconds, which isn't literally true — Earth's rotation occasionally requires a leap second to keep atomic clocks and solar time aligned. Rather than represent that extra second, POSIX time repeats or smears a second instead, meaning the timestamp-to-date mapping is an approximation that diverges from true elapsed time by a handful of seconds over decades, a detail that only matters for astronomical or high-precision timing systems, not typical application code.
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