A Unix timestamp (also called Unix time or epoch time) is a way computers track a specific moment by counting the number of seconds that have passed since midnight UTC on January 1, 1970 — a date known as "the Unix epoch."

Why count from 1970?

The Unix operating system, developed at Bell Labs in the late 1960s and early 1970s, needed a simple, compact way to represent time internally. Counting seconds from a fixed starting point avoids the complexity of calendars, months of different lengths, leap years, and time zones — all of that can be calculated afterward, only when a human needs to read the date.

How it looks in practice

A Unix timestamp is just a number, for example 1700000000. That single number represents an exact instant, identical everywhere in the world — no time zone ambiguity, since it's always measured from UTC. Software converts that number into a human-readable local date and time only at the point of display.

Where you'll encounter Unix time

  • Database records and log files, where storing a single integer is far more efficient than a formatted date string
  • APIs, where timestamps are frequently passed as Unix time to avoid time zone parsing errors between systems
  • Programming languages, nearly all of which include built-in functions to convert to and from Unix time

The "Year 2038 problem"

Older systems that store Unix time as a 32-bit signed integer will run out of room on January 19, 2038, at which point the counter would overflow. Most modern systems have already moved to 64-bit representations, which push the same limit far beyond any practical timeframe, but it's a reminder of why the choice of data format matters even for something as simple as counting seconds.

Quick mental math

As a rough guide, one year is approximately 31,536,000 seconds (or 31,622,400 in a leap year). If you ever need to sanity-check a timestamp, comparing it to a known reference point — such as January 1, 2024 at roughly 1,704,067,200 — can help you tell at a glance whether a number represents a date in the past, present, or far future.