What Is a Unix Timestamp?
A Unix timestamp (also called epoch time or POSIX time) is the number of seconds that have elapsed since January 1, 1970 at 00:00:00 UTC. For example, the timestamp 1700000000 represents November 14, 2023 at 22:13:20 UTC.
Why Was January 1, 1970 Chosen?
The Unix epoch was chosen by the original Unix developers in the late 1960s as a convenient, recently-past reference point. There was no deeper significance — it was simply round and recent enough to be practical for the systems of that era.
The Year 2038 Problem
Many older systems store Unix timestamps as a signed 32-bit integer, which can only count up to 2,147,483,647 seconds after the epoch — that limit is reached at 03:14:07 UTC on January 19, 2038. Systems still using 32-bit timestamps will wrap around to a negative number at that moment, effectively resetting to December 1901. Most modern systems have migrated to 64-bit timestamps, which push the limit out roughly 292 billion years, but embedded systems and older databases can still be affected.
A Common Debugging Trap
The single most frequent Unix timestamp bug is mixing seconds and milliseconds between languages. If you pass a JavaScript millisecond timestamp (13 digits) into a PHP function expecting seconds (10 digits), the resulting date will be roughly 55,000 years in the future rather than throwing an obvious error — the code technically runs, it just silently produces nonsense. Checking the digit count first is the fastest way to catch this before it causes confusing downstream bugs.
Seconds vs Milliseconds
Most Unix timestamps are expressed in seconds (10 digits, e.g. 1700000000). JavaScript and many modern APIs use milliseconds (13 digits, e.g. 1700000000000). Always check which unit an API expects — passing seconds where milliseconds are expected will result in dates in January 1970.
How to Use Timestamps in Code
In PHP: time() returns the current Unix timestamp in seconds. In JavaScript: Date.now() returns milliseconds, Math.floor(Date.now()/1000) gives seconds. In Python: import time; time.time().
Convert Timestamps Instantly
Our Unix Timestamp Converter converts timestamps to UTC, ISO 8601, local time and relative time formats. It also converts any date back to a Unix timestamp with a simple date picker.
