This guide explains unix time in plain language, with the exact figures and how to work them out yourself.
Underneath every human-readable date on your devices sits a single integer: the number of seconds elapsed since 00:00:00 UTC on January 1, 1970 — a moment programmers call the Unix epoch. As this article is written, that counter reads around 1.78 billion. Databases, operating systems, and websites store times this way because one number is unambiguous, easy to compare, and immune to time zone confusion.
The choice of 1970 wasn’t cosmic — it was convenient. Unix was developed at Bell Labs around then, and its engineers picked a recent, round starting point. Every timestamp you see — a message’s “sent at 14:32,” a file’s “modified yesterday” — is that raw number translated into your local time zone at the moment of display.
The system has one famous wrinkle: on systems that store the count as a signed 32-bit integer, the counter overflows on January 19, 2038 — the “Year 2038 problem,” a cousin of Y2K. Modern 64-bit systems have already moved past it, with room to count for hundreds of billions of years.
Fun milestones pass quietly: the counter hit 1,000,000,000 in September 2001 and 1,500,000,000 in July 2017, with 2,000,000,000 due in May 2033. Developers sometimes gather online to watch round numbers tick over — the nerdiest New Year’s Eve there is.
Frequently asked questions
Related on itsdately: What Is a Leap Second — and Why It's Being Retired · From Milliseconds to Attoseconds: The Small Units of Time · The 23-Hour-56-Minute Day: Solar vs Sidereal Time
Further reading: The Open Group POSIX specification