What Is a Unix Timestamp?

A Unix timestamp (also called Epoch time or POSIX time) is a way of representing a specific moment in time as a single integer — the number of seconds that have elapsed since midnight on January 1, 1970, UTC. This date is called the Unix Epoch.

For example, the timestamp 1700000000 corresponds to November 14, 2023, at 22:13:20 UTC. Timestamps are language-agnostic, timezone-independent, and perfectly suited for storing time in databases and APIs where human-readable formats would create ambiguity or require complex parsing.

Why Developers Use Unix Timestamps

• No timezone ambiguity — a timestamp is always UTC. Timezone conversion happens at display time, not storage time.
• Easy arithmetic — subtracting two timestamps gives the difference in seconds. No date parsing required.
• Universal support — every programming language and database natively supports Unix timestamps.
• Compact storage — an integer takes less space than a formatted date string in a database.
• Sorting — timestamps sort naturally as integers, no special date-aware sorting needed.

Milliseconds vs Seconds — A Common Source of Bugs

Different systems use different precision for timestamps. Unix traditionally uses seconds, but JavaScript's Date.now() returns milliseconds. This is a common source of bugs — a timestamp like 1700000000000 (milliseconds) would be interpreted as the year 55,000+ if treated as seconds.

A quick rule: if your timestamp is 13 digits, it is in milliseconds. If it is 10 digits, it is in seconds. Divide by 1000 to convert milliseconds to seconds when needed.

The Year 2038 Problem

Systems that store Unix timestamps as a 32-bit signed integer can only represent dates up to January 19, 2038 — after which the integer overflows and wraps to a negative number, causing the date to jump back to 1901. This is known as the Year 2038 Problem (Y2K38). Modern systems using 64-bit integers are not affected and can represent dates hundreds of billions of years into the future.