Unix timestamp to date converter

A Unix timestamp counts the seconds since 1 January 1970 in UTC. It is how databases and APIs store time, but it is unreadable for people.

Here you translate in both directions.

The value is read as seconds, and if it exceeds a hundred billion it is assumed to be in milliseconds. Every output is expressed in UTC to avoid time zone ambiguity.

Unix time counts seconds since 1970

The origin was fixed at midnight on 1 January 1970 UTC, a date chosen for practical convenience when the system was designed. Every later moment is a positive number of seconds and every earlier one negative. It is the simplest possible way to represent an instant without ambiguity.

Why always UTC

A timestamp has no time zone: it is an absolute instant. Conversion to local time happens when displaying it, applying the user's zone. Storing dates in local time is the number one source of errors in international applications, because the same number means different things depending on where it is read.

The year 2038 problem

Systems storing the timestamp in a signed thirty-two bit integer overflow on 19 January 2038, jumping to negative numbers. It is the modern equivalent of the Y2K bug, and is solved by migrating to sixty-four bit integers, which most modern systems have already done.

Leap seconds

Unix time ignores the leap seconds occasionally added to align atomic clocks with the Earth's rotation. It is a deliberate simplification that avoids complications at the cost of minimal imprecision.