Unix Timestamp Converter

A Unix timestamp is an integer that counts the number of seconds (or milliseconds) that have elapsed since January 1, 1970, 00:00:00 UTC — known as the Unix epoch. It is timezone-independent, making it a reliable way to store and compare moments in time across systems and programming languages.

The Unix epoch was chosen by the designers of the Unix operating system in the early 1970s. January 1, 1970, 00:00:00 UTC was a convenient, recent reference point that predated the system's development. The exact date was somewhat arbitrary — the important property was that it was a fixed, universally agreed-upon origin for counting time.

The Year 2038 problem (Y2K38) affects systems that store Unix timestamps in a signed 32-bit integer. Such integers can hold values up to 2,147,483,647, which corresponds to January 19, 2038, 03:14:07 UTC. After that moment the value overflows to a large negative number, potentially causing crashes or incorrect date calculations. Modern systems use 64-bit integers, which can safely represent dates hundreds of billions of years into the future.

A Unix timestamp in seconds is a 10-digit number (e.g., 1700000000). Many languages and APIs — including C, Python's time.time(), and most Unix utilities — use seconds. JavaScript's Date.now() and Java's System.currentTimeMillis() return milliseconds instead, producing a 13-digit number (e.g., 1700000000000). This tool auto-detects which format you've entered: numbers over 1 trillion (13+ digits) are treated as milliseconds.

Languages vary in their default resolution. JavaScript and Java use milliseconds (Date.now(), System.currentTimeMillis()). Python offers both: time.time() returns a float in seconds, while datetime.timestamp() does too. Go's time.Now().Unix() returns seconds; time.Now().UnixMilli() returns milliseconds. PHP's time() returns seconds. Ruby's Time.now.to_i returns seconds. When working across language boundaries always confirm which resolution is expected to avoid off-by-1000 errors.