Unix Timestamp Converter
Convert a Unix timestamp to a readable date in every common format, or go the other way. Seconds and milliseconds are detected automatically.
Your data never leaves your browser. This tool runs entirely on your device.
Enter a Unix timestamp.
Seconds versus milliseconds
This is the bug this tool exists to catch. A conventional Unix timestamp counts seconds and currently has 10 digits. JavaScript's Date.now() returns milliseconds and has 13.
Mix them up and the error is spectacular rather than subtle: a millisecond value read as seconds lands around the year 55,000, and a seconds value read as milliseconds lands in January 1970. The converter guesses from the digit count and tells you which it assumed.
1700000000 → 10 digits → seconds 1700000000000 → 13 digits → milliseconds
Why timestamps have no time zone
A Unix timestamp is a count of seconds from a single fixed instant, so it identifies a moment unambiguously everywhere on Earth. That is what makes it the correct thing to store in a database.
A time zone is a display concern, applied only when showing the value to a person. Storing local times creates ambiguity every autumn, when the same wall-clock hour occurs twice.
Leap seconds and the year 2038
Unix time assumes every day is exactly 86,400 seconds long, so leap seconds are simply not represented. This keeps arithmetic simple at the cost of drifting slightly from astronomical time.
Systems storing timestamps as a signed 32-bit integer overflow at 03:14:07 UTC on 19 January 2038 and wrap around to 1901. Modern 64-bit systems are unaffected, but embedded devices and legacy file formats may not be.
Frequently asked questions
How do I know if my timestamp is in seconds or milliseconds?
Count the digits. Current timestamps in seconds have 10; in milliseconds, 13. This converter detects it automatically and tells you which it used, and you can override the guess.
What is the Unix epoch?
00:00:00 UTC on 1 January 1970, the zero point from which Unix timestamps are counted. A negative timestamp is a moment before it.
What time zone does a Unix timestamp use?
None. It is an absolute count from a fixed instant, equivalent to UTC. A time zone is applied only when converting it for display.
What is the 2038 problem?
A signed 32-bit integer can hold seconds only until 03:14:07 UTC on 19 January 2038, after which it wraps to 1901. Systems using 64-bit time values, which is nearly all modern software, are unaffected.
Why does my JWT expiry look wrong?
JWT exp and iat claims are in seconds, not milliseconds. Passing a JavaScript Date.now() value directly produces a token that expires 50,000 years from now, which some verifiers reject outright.
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