Explainer1 min readUpdated June 29, 2026

What is a Unix timestamp?

Short answer

A Unix timestamp is the number of seconds that have passed since 00:00:00 UTC on 1 January 1970, a moment called the epoch. It is a simple, timezone-free way for computers to store and compare points in time.

One number, no timezone

Instead of storing a date as text, many systems store a single integer: the count of seconds since the epoch. Because it is measured in UTC, the same timestamp means the same instant everywhere, and timezones are applied only when a human needs to read it.

1751155200  =  2025-06-29 00:00:00 UTC

A timestamp and its meaning

Try it: Timestamp ConverterConvert between Unix timestamps and human-readable dates locally.Open tool

Seconds or milliseconds

Classic Unix time counts whole seconds, but many languages, including JavaScript, work in milliseconds, giving a 13-digit number instead of 10. If a timestamp looks a thousand times too big, it is probably in milliseconds.

The year 2038 problemA 32-bit signed integer can only count seconds up to 19 January 2038. Modern systems use 64-bit integers to avoid overflowing on that date.

References

Questions

Why does my timestamp have 13 digits?

It is likely in milliseconds, not seconds. Divide by 1000 to get the classic 10-digit Unix timestamp in seconds.

Is a Unix timestamp affected by timezones?

No. It always refers to UTC. Timezone offsets are only applied when converting it to a local, human-readable date.

Does this send my data anywhere?

No. Utilumo's developer tools parse and transform input inside the browser tab. Nothing is uploaded, stored, or logged.