Epoch time in one paragraph
A Unix timestamp counts the seconds since 1970-01-01 00:00:00 UTC, ignoring leap seconds. Many languages and APIs use seconds; JavaScript and some databases use milliseconds. This tool treats numbers below 100 billion as seconds and larger ones as milliseconds, which covers dates from 1970 to the year 5138 in seconds.
Time zones
A timestamp has no time zone; it identifies one instant. The converter shows that instant in UTC and in your browser's local time. Dates you type without a zone are read as UTC so results do not depend on your device.
The year 2038 problem
Systems that store seconds in a signed 32-bit integer overflow on 2038-01-19 at 03:14:07 UTC. Modern 64-bit systems are not affected.