Example
Input
1715600000
Output (both directions)
Unix (seconds): 1715600000 Unix (milliseconds): 1715600000000 ISO 8601: 2024-05-13T13:33:20.000Z UTC: Mon, 13 May 2024 13:33:20 GMT Local: 2024-05-13 22:33:20 (KST)
Note
10-digit input is seconds, 13-digit is milliseconds (auto-detected). Date strings in ISO 8601, RFC 2822, or freeform formats are also accepted.
Usage / FAQ
When to use
- Make Unix timestamps in API responses (JWT exp, MongoDB ObjectId, …) human-readable
- Convert DB log epoch times to your local timezone
- Generate the current timestamp with one click (now button)
- Round-trip ISO 8601 ↔ epoch while debugging
- Represent absolute time independent of timezone
FAQ
- Q.How are seconds vs milliseconds distinguished?
- A.By digit count — 10 digits = seconds, 13 = milliseconds. JavaScript Date uses ms; Unix / Python's `time.time()` uses seconds. The most common 1000× bug.
- Q.What is Y2K38?
- A.The 32-bit signed int rolls over on Jan 19, 2038 at 03:14:07 UTC. Modern 64-bit timestamps are safe for ~290 billion years.
- Q.What if the timestamp is negative?
- A.It's a moment before 1970-01-01. E.g. -86400 is 1969-12-31. Some legacy systems can't handle negative epoch times — be careful.
Fun facts
1970-01-01 00:00:00 UTC is the Unix epoch — set by Bell Labs while building PDP-11 Unix. Curiously, the *first* Unix Programmer's Manual (Nov 1971) used a 1971-01-01 epoch before settling on 1970.
Wikipedia — Unix timeAt 2038-01-19 03:14:07 UTC, signed 32-bit Unix time overflows. Dubbed the 'Year 2038 problem' — Y2K's successor — and very real for embedded systems and `int32` DB columns. 64-bit time has another ~290 billion years of headroom.
Y2038 problemUnix time ignores leap seconds. UTC and Unix time diverge by the accumulated leap-second count (27 seconds as of 2025), and at a leap-second event Unix time effectively repeats the same second rather than expressing `23:59:60`.
Wikipedia — Leap second
Related guides
- UUID vs ULID — Which Identifier Should You Use?
UUID v4, UUID v7, ULID, and Snowflake compared on sortability, database performance, URL friendliness, and collision risk.
- Cron Expression Guide — Syntax, Timezones, and Common Mistakes
Cron field-by-field syntax, special tokens, timezone behavior across Unix cron, Kubernetes, and AWS, and the patterns that cause silent failures.
- Timezone Pitfalls in JavaScript — UTC, IANA, DST, and Storing Dates Right
Why JS Date is dangerous, why you should always store UTC, the difference between offset and IANA name, daylight saving traps, and the right way to format for users.
- How Unix Time Actually Works
Why 1970, why Unix time isn't actually monotonic, the Y2038 problem on 32-bit systems, the leap-second mess, monotonic vs wall clocks, and why "now()" can go backwards.
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