What Is Unix Time?

Unix time counts the seconds since the epoch: 00:00:00 UTC on 1 January 1970. The date has no cosmic significance — it was simply a convenient round number chosen by the developers of Unix at Bell Labs in the early 1970s. Five decades later it is the de-facto standard for machine timekeeping: file modification times, database rows, JWT expiries, log lines and HTTP caches all speak epoch.

Its appeal is that a timestamp is just an integer. Comparing, sorting and subtracting times become integer operations, and the value means the same instant everywhere on Earth — timezones only enter the picture when a time is displayed to a human. Try it live in our epoch converter.

The Year 2038 problem

Early Unix stored the counter in a signed 32-bit integer, which holds a maximum of 2,147,483,647. That count is reached at 03:14:07 UTC on 19 January 2038; one second later the value wraps negative and a vulnerable system believes it is 13 December 1901. Modern 64-bit systems are safe for roughly 292 billion years, but 32-bit values survive in embedded devices, old file formats, database column types and binary protocols — making 2038 a slow-motion, smaller-scale sequel to Y2K. Auditing for 32-bit time storage is the entire fix.

Leap seconds

Earth's rotation drifts relative to atomic clocks, so UTC occasionally inserts a leap second. Unix time pretends these don't exist: every day is exactly 86,400 seconds. During a leap second the clock either repeats a second or, in large fleets, "smears" it across the surrounding hours. The benefit is arithmetic simplicity; the cost is that subtracting two Unix timestamps across a leap second is off by one physical second — irrelevant for almost everything except scientific timekeeping.

Common units

Seconds are standard, but JavaScript's Date.now() returns milliseconds, and high-resolution tracing uses microseconds or nanoseconds. A timestamp's digit count usually reveals its unit — 10 digits today means seconds, 13 means milliseconds. Get the current epoch in Python, JavaScript, Go and 17 other languages.

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