Unix Timestamps: The Developer's Complete Guide

Unix timestamps are the universal language of time in computing. Here is everything you need to know.

What Is a Unix Timestamp

A Unix timestamp is the number of seconds that have elapsed since January 1, 1970, 00:00:00 UTC (the Unix epoch). It is a single integer that represents a precise moment in time, independent of time zones.

Seconds vs Milliseconds

Unix timestamps are traditionally in seconds. JavaScript and Java use milliseconds. If you see a 10-digit number, it is seconds. A 13-digit number is milliseconds. Getting this wrong is one of the most common timestamp bugs.

The 2038 Problem

A 32-bit signed integer overflows on January 19, 2038 at 03:14:07 UTC. Any system still using 32-bit timestamps will wrap around to a negative number, representing a date in 1901. Most modern systems use 64-bit timestamps, but legacy embedded systems and databases may still be vulnerable.

Time Zones and UTC

Always store timestamps in UTC. Convert to local time only for display. Storing local times leads to ambiguity during daylight saving transitions and makes comparison between records in different zones impossible.

Common Operations

Get current timestamp: Date.now() / 1000 in JavaScript, time.time() in Python, time() in PHP. Convert to human date: pass the timestamp to your language Date constructor. Use our Unix Timestamp Converter tool for quick conversions without writing code.

Leap Seconds

Unix timestamps do not account for leap seconds. UTC occasionally adds a second to stay synchronized with Earth rotation. In practice this rarely matters, but if you need sub-second precision across long time spans, be aware of this limitation.