Almost every API you'll ever hit returns dates as a big integer like 1735689600. That's a Unix timestamp — and once you understand it, dates in software stop being confusing.
What it is
A Unix timestamp is the number of seconds elapsed since **January 1, 1970 at 00:00 UTC** (the "epoch"). It has no timezone. It's just a count.
Why it's used everywhere
- One universal number — no timezone bugs at the storage layer.
- Cheap to compare, sort and math on.
- Every language has a built-in for it.
Seconds vs milliseconds
- 10 digits → seconds (e.g. `1735689600`).
- 13 digits → milliseconds (e.g. `1735689600000`). JavaScript uses milliseconds.
Convert instantly
Use [Unix Timestamp Converter](/tools/unix-timestamp) — paste a number and get your local time and UTC, or paste a date and get its timestamp.
The Year 2038 problem
32-bit signed timestamps overflow on January 19, 2038. Modern systems use 64-bit ints and are fine for the next ~292 billion years.
