What a Unix timestamp is
A Unix timestamp counts the seconds since 00:00:00 UTC on 1 January 1970, ignoring leap seconds. It has no time zone: 1700000000 is the same instant everywhere on Earth, which is why databases, logs, JWT claims and APIs use it to store times.
Many systems use milliseconds instead. JavaScript's Date.now(), Java's System.currentTimeMillis() and most browser APIs return 13-digit millisecond values, while Unix tools, Python's time.time() and JWT claims use 10-digit seconds. The converter detects seconds, milliseconds, microseconds or nanoseconds from the number of digits and tells you which it used.
Reading the result
Every result has its own copy button: Unix seconds and milliseconds, ISO 8601 in UTC (such as 2023-11-14T22:13:20.000Z, where the Z means UTC), ISO 8601 with the offset of the zone you choose, a readable date, the HTTP date format used in headers, and a relative time such as "3 hours ago".
To convert the other way, paste an ISO date like 2024-03-01T09:30:00Z, or use the date picker. The picker reads the time in the selected time zone, so you can answer questions like "what timestamp is 9:00 in New York" without doing offset maths. A typed date without a Z or offset is read in your browser's local time zone.
The year 2038 problem
Systems that store timestamps in a signed 32-bit integer run out of room at 03:14:07 UTC on 19 January 2038, when the count passes 2,147,483,647 and wraps to a date in 1901. Modern platforms use 64-bit values, but embedded devices, old database columns and file formats can still be affected, so check the column types in anything expected to outlive 2038.
