What Is a Unix Timestamp? (Epoch Time Explained)

Why start in 1970?

The date was chosen by the early Unix developers as a convenient round starting point. Timestamp 0 is 1970-01-01 00:00:00 UTC, 86400 is exactly one day later, and negative numbers mean dates before 1970.

Because it is just a count, working out how long something took is simple subtraction: end timestamp minus start timestamp gives the seconds in between.

Seconds or milliseconds?

Most systems use seconds, which are currently 10 digits long. JavaScript and many web APIs use milliseconds, which are 13 digits: 1700000000000 is the same moment as 1700000000.

The Timestamp Converter checks the size of the number: values below one trillion are treated as seconds and larger ones as milliseconds, so both work.

Timestamps have no time zone

A timestamp is the same everywhere in the world at the same instant. The time zone only appears when you turn it into a readable date. 1700000000 is 22:13 in London but 17:13 in New York on the same day.

That is why the converter shows the date in your device's local time — a friend in another country entering the same number sees their own local clock time for that moment.

The year 2038 problem

Older systems store timestamps in a signed 32-bit number, whose largest value is 2147483647 — reached on January 19, 2038 at 03:14:07 UTC. After that, those systems could wrap around to 1901.

Modern systems use 64-bit numbers, which last for billions of years, so most current software is already safe.

Convert both ways

Paste a number into Unix timestamp to see the readable date, or pick a date and time to get its timestamp. Press Use current time to fill in the present moment.