Unix Timestamp Converter

A Unix timestamp (also called epoch time or POSIX time) is a single integer representing the number of seconds elapsed since January 1, 1970 at 00:00:00 UTC — a moment known as 'the Unix epoch'. The convention dates back to the early Unix operating system at Bell Labs in the 1970s. Its value over human-readable dates is that it's a single number, timezone-agnostic, easy to compare and arithmetic on, and unambiguous across systems. Every modern database, log file, JWT, OAuth token, and most APIs use Unix timestamps internally. The 'exp' claim in a JWT is a Unix timestamp; the 'created_at' in most APIs is a Unix timestamp or ISO 8601 string derived from one; file modification times on Linux/macOS are stored as Unix timestamps. There are two common variants you must distinguish: seconds (the original Unix convention, used in JWTs, OAuth, Linux file metadata) and milliseconds (used in JavaScript's Date.now(), Java's System.currentTimeMillis(), and many modern APIs). A 10-digit timestamp is seconds; a 13-digit timestamp is milliseconds. This tool handles both — paste either format in either field and we'll auto-detect and convert. The other concept worth knowing: ISO 8601 is the standard human-readable format (2025-12-31T23:59:59Z) — strictly ordered alphabetically and parseable everywhere. When given a choice between storing timestamps as Unix integers or ISO 8601 strings, prefer Unix for performance and ISO 8601 for human readability.