Free Online Unix Timestamp Converter
Runs in this tab. A token, a key, a config — whatever you paste stays local.
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How it works
Seconds or milliseconds, the classic bug
The epoch is defined in seconds, and Unix tools, JWT claims and most APIs use seconds. JavaScript's Date.now() and Java's System.currentTimeMillis() return milliseconds. Mixing them is the single most common date bug in production: treat milliseconds as seconds and you land in the year 57 000; treat seconds as milliseconds and everything happened in January 1970. Digit count is the tell — a current timestamp is 10 digits in seconds and 13 in milliseconds.
- Seconds
- 10 digits for any date between 2001 and 2286. What crontabs, JWT exp and most REST APIs mean by a timestamp.
- Milliseconds
- 13 digits today. JavaScript, Java and most browser APIs. Microseconds (16 digits) show up in some databases too.
- UTC and local
- Both shown together, with the offset, so a timestamp is never ambiguous about which zone you are reading.
- ISO 8601
- Output as 2026-08-16T12:00:00Z. The trailing Z means UTC; without an offset a string is a local time and travels badly.
- 2038
- A signed 32-bit counter overflows at 03:14:07 UTC on 19 January 2038. Systems still storing time in an int32 wrap to 1901.
How to use it
How to convert a Unix timestamp online
- 01
Paste the timestamp
Seconds or milliseconds is detected from the digit count, and can be overridden.
- 02
Read both zones
UTC and your local time appear together, with the offset in effect on that date.
- 03
Or go the other way
Enter a date and time and take the epoch value in either unit.
Where it earns its keep
Where timestamp conversion comes up
- Reading epoch timestamps in an application log or a trace.
- Checking a JWT's exp claim against the actual time it expired.
- Setting an expiry value in a database seed or a cache entry by hand.
- Working out whether an incident window in UTC lines up with a local report.
Questions
Timestamp Converter, answered
How do I tell seconds from milliseconds?
By length: a present-day timestamp is 10 digits in seconds and 13 in milliseconds. We detect it from the digit count, but the guess is only a heuristic — a genuine second-based timestamp far in the future looks the same, so you can override it.
Does the conversion happen on a server?
No. It is arithmetic and the browser's own time zone data, run in this tab. Nothing is sent, and it works offline.
Do Unix timestamps account for leap seconds?
No, and that is deliberate. Unix time pretends every day is exactly 86 400 seconds, so a leap second is absorbed rather than counted. It is not a true count of elapsed SI seconds since 1970.
What is the 2038 problem?
A signed 32-bit time_t runs out at 03:14:07 UTC on 19 January 2038 and wraps to 1901. Modern 64-bit systems are fine, but embedded devices, old database columns and some file formats still store time in 32 bits.