Question 1

What is a Unix timestamp?

Accepted Answer

The number of seconds since 1 January 1970 at 00:00:00 UTC, not counting leap seconds. Many programs, logs and databases store time this way. A date before 1970 is a negative number.

Question 2

How does it know if my number is seconds or milliseconds?

Accepted Answer

By its length. Up to 11 digits is read as seconds, 12 to 14 digits as milliseconds, and longer as microseconds. The page says which it assumed, and you can switch the unit yourself if it guessed wrong.

Question 3

Why does 2147483647 matter?

Accepted Answer

It is the largest number a signed 32-bit integer can hold. As a timestamp it is 19 January 2038 at 03:14:07 UTC. Systems that store time in 32 bits stop working correctly after that moment.

Question 4

What happens with a time the clocks skip or repeat?

Accepted Answer

When the clocks go forward, a time in the skipped hour does not exist, so it moves forward by the gap. When they go back, a time in the repeated hour happens twice, so the first one is used. The page tells you when this happens.

Question 5

Is my data uploaded anywhere?

Accepted Answer

No. Everything runs in your browser tab, and the page's security policy blocks it from sending data anywhere.

Runs	In your browser. Your files stay on your device.
Units	Seconds, milliseconds and microseconds, guessed from the length of the number
Range	Years 1 to 9999, including dates before 1970
Engine	Your browser's Date and Intl, with its time zone database
Works offline	Yes, once the page has loaded
Licence	AGPL-3.0
Added	11 October 2026
Built by	Sapience Design
Source	tools/everyday/unix-timestamp

Convert a Unix timestamp to a date

Timestamp to date

Date to timestamp

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