Unix Timestamp Complete Guide

A comprehensive guide to Unix timestamps, their history, usage, and implementation across different systems and programming languages. Learn about UTC time and time units for complete understanding.

What is a Unix Timestamp?

A Unix timestamp is a way to track time as a running total of seconds. This count starts at the Unix Epoch on January 1st, 1970 at UTC. Therefore, the Unix timestamp is merely the number of seconds between a particular date and the Unix Epoch.

Unix timestamps are signed integers that can represent dates before 1970 as negative numbers and dates after 1970 as positive numbers.

History and Origin

The Unix timestamp system was created along with the Unix operating system in the early 1970s at Bell Labs. The choice of January 1, 1970, as the epoch was somewhat arbitrary but has become the standard reference point for computer systems worldwide. This forms the basis of Unix time.

The system was designed to be simple, efficient, and unambiguous - qualities that have made it the foundation for timekeeping in modern computing.

Seconds vs Milliseconds

Traditional Unix timestamps count seconds, but many modern systems use milliseconds for greater precision:

• Seconds: 10-digit numbers (e.g., 1640995200).
• Milliseconds: 13-digit numbers (e.g., 1640995200000).

JavaScript, for example, uses milliseconds by default, while most Unix systems use seconds. Our converter tool handles both formats automatically.

Advantages of Unix Timestamps

• Universal: Works across all time zones and systems.
• Simple: Just an integer, easy to store and compare.
• Efficient: Fast calculations and minimal storage space.
• Unambiguous: No confusion about format or timezone.
• Sortable: Chronological order matches numerical order.

Common Use Cases

Unix timestamps are essential in many areas of computing:

• Database record creation and modification times.
• API rate limiting and caching expiration.
• Log file timestamps and system monitoring.
• Session management and authentication tokens.
• File system metadata and backup systems.

The Year 2038 Problem

Traditional 32-bit Unix timestamps will overflow on January 19, 2038, at 03:14:07 UTC. This is similar to the Y2K problem but affects Unix systems specifically.

Most modern systems have migrated to 64-bit timestamps, which won't overflow for approximately 292 billion years, effectively solving this problem.

Working with Unix Timestamps

When working with Unix timestamps, remember:

• Always store timestamps in UTC to avoid timezone issues.
• Be consistent with seconds vs milliseconds in your application (see time units guide).
• Use appropriate data types to avoid overflow.
• Consider leap seconds for high-precision applications. Get current timestamps for testing.

See Unix timestamp examples in all programming languages

Convert Unix timestamps to dates