Unix Timestamps Explained: Epoch Time for Developers
2026-06-03 · 5 min read
That big number in your logs is Unix time. Here is how it works, why it has no timezone, and the famous 2038 bug.
A Unix timestamp is the number of seconds that have elapsed since 1 January 1970 at 00:00:00 UTC, known as the epoch. It is the most common way computers store and exchange time.
Seconds vs milliseconds
Unix time is traditionally in seconds (10 digits today), but JavaScript and many APIs use milliseconds (13 digits). Mixing them up is a classic bug — a millisecond value read as seconds lands thousands of years in the future.
It has no timezone
A timestamp always refers to a single instant in UTC. The same timestamp displays as different wall-clock times around the world. Convert to local time only when displaying it to a user.
The year 2038 problem
Systems that store timestamps as a signed 32-bit integer will overflow on 19 January 2038. Modern systems use 64-bit integers, which pushes the limit billions of years out.
When storing time, store UTC timestamps and convert for display. Storing local time without an offset is a frequent source of bugs.
Convert in both directions
The Timestamp Converter turns epoch values into readable local, UTC, and ISO dates — and converts dates back to timestamps — with automatic seconds/milliseconds detection.