What Is Unix Time (Epoch Time)?
One-line definition: Unix time is the number of seconds elapsed since January 1, 1970 at 00:00:00 UTC. It's currently past 1.78 billion — growing by 1 every second. It's timezone-neutral: the same value everywhere on Earth.
What Unix Time Is
Also called epoch time or POSIX time, Unix time is a single integer representing a moment in time as a count of seconds from a fixed starting point — January 1, 1970 at midnight UTC. The number 1780000000 refers to the same instant in every timezone on Earth.
Computers prefer integers over strings. Comparing two Unix timestamps is a single arithmetic operation. Comparing two date strings like “June 4, 2026 9:02 AM EDT” and “2026-06-04T14:02:00+05:30” requires parsing, timezone conversion, and then comparison. Unix time removes all of that.
Seconds vs Milliseconds
Traditional Unix timestamps are in seconds — 10-digit numbers. JavaScript's Date.now() returns milliseconds — 13-digit numbers. This mismatch causes bugs when a JavaScript app passes a millisecond timestamp to a system expecting seconds.
Divide a 13-digit timestamp by 1,000 to get seconds. The epoch time converter auto-detects both formats.
Notable Epoch Values
| Timestamp | Date (UTC) | Note |
|---|---|---|
| 0 | Jan 1, 1970 00:00:00 | The Unix epoch |
| 1,000,000,000 | Sep 9, 2001 01:46:40 | "Billennium" |
| 1,500,000,000 | Jul 14, 2017 02:40:00 | One and a half billion |
| 2,000,000,000 | May 18, 2033 03:33:20 | Two billion milestone |
| 2,147,483,647 | Jan 19, 2038 03:14:07 | 32-bit overflow (Y2K38) |
Y2K38: 32-bit signed integers overflow in 2038. Modern 64-bit systems are not affected.
Frequently Asked Questions
What is Unix time?
Unix time is the number of seconds elapsed since January 1, 1970 at 00:00:00 UTC. It's timezone-neutral — the same value in New York, London, and Tokyo for any given moment.
How is Unix time different from a regular timestamp?
A regular timestamp (like "June 4, 2026 9:00 AM EST") includes human-readable components and a timezone. Unix time is a single integer representing the same moment without any timezone ambiguity — ideal for system storage and calculation.
What happens in 2038?
On January 19, 2038, 32-bit signed Unix timestamps overflow to a large negative value. Modern systems using 64-bit integers are not affected — they can store timestamps until the year 292 billion. But older embedded systems and legacy databases on 32-bit architectures need updates.
Is Unix time the same as epoch time?
Yes — Unix time, epoch time, POSIX time, and Unix timestamp all refer to the same thing: seconds since January 1, 1970 UTC.