Unix Timestamps Explained

What a Unix timestamp is

A Unix timestamp is the number of seconds that have passed since 1 January 1970 at 00:00:00 UTC, a moment known as the Unix epoch. 1700000000 corresponds to 14 November 2023, 22:13:20 UTC.

Because it is just a count of seconds, it is easy to store, sort and compare, and it means the same moment everywhere in the world.

Seconds or milliseconds?

Many systems count seconds, but JavaScript (Date.now()), Java (System.currentTimeMillis()) and many APIs use milliseconds. Present-day timestamps have 10 digits in seconds and 13 digits in milliseconds.

Mixing them up is a classic bug: a seconds value read as milliseconds lands in January 1970, and a milliseconds value read as seconds lands tens of thousands of years in the future.

Timestamps have no time zone

A timestamp marks a moment, not a clock reading. The time zone only matters when you display it. The same 1700000000 is 22:13 on 14 November in London (UTC in winter) and 03:43 on 15 November in India, because IST is UTC + 5:30.

Store and transmit timestamps (or ISO 8601 strings with a time-zone offset), and convert to local time only for display.

Convert a timestamp

With Timestamp Converter:

1. Paste the number — seconds or milliseconds are detected automatically.
2. Read the date in your local time, in UTC, in ISO 8601 and in other time zones, including India.
3. To go the other way, enter a date and time to get the timestamp.

The year-2038 problem

Old systems that store timestamps as signed 32-bit integers can count only up to 2,147,483,647 seconds — reached on 19 January 2038. After that the number overflows. Modern systems use 64-bit values and are not affected, but old databases, embedded devices and file formats can be.