What is a Unix timestamp?+
A Unix timestamp (also called epoch time, POSIX time, or Unix time) is the number of seconds that have elapsed since 00:00:00 UTC on January 1, 1970, not counting leap seconds. It's the standard way computers represent points in time, and it's timezone-agnostic — the same instant in time has the same Unix timestamp everywhere on Earth.
What's the difference between seconds and milliseconds in a timestamp?+
Standard Unix timestamps are in seconds (10 digits for current dates, e.g. 1750000000). JavaScript and many modern APIs use milliseconds (13 digits, e.g. 1750000000000). Microseconds (16 digits) are used in some Python libraries and Unix microsecond timestamps. The converter auto-detects unit by digit count, but you can also pick explicitly.
What is ISO 8601?+
ISO 8601 is the international standard for representing dates and times as strings. The most common form is YYYY-MM-DDTHH:mm:ss.sssZ (e.g. 2026-06-20T14:30:00.000Z). The 'T' separates the date from the time; the trailing 'Z' means UTC. ISO 8601 strings are unambiguous, sortable as strings, and parseable in every major language.
When will the Unix timestamp overflow?+
On 03:14:07 UTC on January 19, 2038, 32-bit signed integers storing seconds since 1970 will overflow — the so-called Year 2038 Problem. Modern systems use 64-bit integers, which won't overflow for about 292 billion years. If you're working with a system that still stores timestamps in a 32-bit field, that field will need migration before 2038.
What timezone does my browser use?+
Your browser uses the timezone configured on your operating system. JavaScript's Intl.DateTimeFormat().resolvedOptions().timeZone returns this value (shown in the 'Local' column above). It can differ from your IP-based geolocation if you've manually set a timezone or are using a VPN.
Does this converter work offline?+
Yes. Once the page has loaded, you can disconnect from the internet and continue using it. All conversions happen in your browser with vanilla JavaScript — no data ever leaves your device. Timezone calculations use the built-in Intl API, which ships with every modern browser.