Understanding Unix Time
Unix Time, also referred to as Epoch time or POSIX time, is a system for tracking time across global computer systems. It represents a single point in time as the total number of seconds elapsed since a specific historical moment.
The Epoch Moment
January 1st, 1970 at 00:00:00 Coordinated Universal Time (UTC)
Why Use Unix Time?
Interpreting human dates like "Sunday, July 4th at 2:30 PM" is incredibly complex for computers due to time zones, leap years, and varying regional formats. Unix time simplifies this into a single, ever-increasing integer. This makes it the standard choice for:
- Database Storage: Sorting events chronologically is extremely fast with integers.
- Server Communication: Ensuring two servers in different countries agree on exactly when an event occurred.
- Programming Logic: Calculating the difference between two timestamps (e.g., "how many days since login") becomes simple subtraction.
The 10-Digit vs. 13-Digit Difference
One of the most common points of confusion is whether to use seconds or milliseconds.
- Classic Unix (Seconds): The original standard. Timestamps are 10 digits long (e.g., 1678886400). Used by systems like PHP, Python, and Linux kernels.
- Modern Unix (Milliseconds): Used primarily by web technologies like JavaScript and Java. Timestamps are 13 digits long.
Our converter automatically detects the length of your input to ensure you don't have to perform math manually.
The Year 2038 Problem
Old 32-bit systems store time in an integer that caps at 2.1 billion. On Jan 19, 2038, these systems will overflow and reset to 1901. Modern 64-bit systems have largely fixed this.
Pro-Tip: UTC
Always save timestamps in UTC in your database, and only convert to the user's local time at the final moment of display.
Frequently Asked Questions
Does Unix time include leap seconds?↓
Strictly speaking, Unix time does not track leap seconds. It ignores them by assuming every day has exactly 86,400 seconds, which keeps its calculation simple.
What is currently happening to Unix time?↓
It is increasing by 1 every single second. Right now, it is approaching 2 billion!
Can Unix time be negative?↓
Yes. Negative unix timestamps represent dates occurring before January 1, 1970.