Unix Timestamp Calculator
A Unix timestamp is the number of seconds since 00:00:00 UTC on 1 January 1970, the moment known as the Unix epoch. It is how most computers store an instant in time as a single integer, free of any time zone. Enter a timestamp to read its UTC date and time, and the elapsed days since the epoch. The calculator also shows the millisecond form used by environments such as JavaScript, which is exactly one thousand times the seconds value. All conversions are deterministic and based on the POSIX definition of time.
Unix timestamp formula
Milliseconds = seconds * 1,000
UTC date = epoch (1970-01-01 00:00:00 UTC) + seconds
Days since epoch = seconds / 86,400
Years since epoch = days / 365.25
There are 86,400 seconds in a day (60 * 60 * 24). The conversion to a calendar date uses the standard proleptic Gregorian calendar in UTC, exactly as the POSIX standard prescribes. Leap seconds are not counted, by definition of Unix time.
Unix time context
- Timestamp 0 is 00:00:00 UTC on 1 January 1970, the Unix epoch.
- One day is exactly 86,400 seconds in Unix time; leap seconds are ignored.
- JavaScript and many APIs use milliseconds (seconds * 1,000) rather than whole seconds.
- A signed 32-bit timestamp overflows at 03:14:07 UTC on 19 January 2038 (the Year 2038 problem).
- Unix time is always UTC; add your local UTC offset for local display.
Unix timestamps: frequently asked questions
What is a Unix timestamp?
A Unix timestamp (also called epoch time or POSIX time) is the number of seconds that have elapsed since 00:00:00 UTC on 1 January 1970, not counting leap seconds. It is a single integer that represents a moment in time independent of any time zone, which makes it the standard way computers store and exchange instants.
What is the Unix epoch?
The Unix epoch is the reference point 00:00:00 Coordinated Universal Time (UTC) on 1 January 1970. Timestamp 0 corresponds exactly to this moment. Times after the epoch are positive integers and times before it are negative.
What is the difference between seconds and milliseconds timestamps?
Classic Unix time counts whole seconds since the epoch. Many programming environments, such as JavaScript's Date.now(), instead count milliseconds since the epoch. A milliseconds value is exactly 1,000 times the seconds value. This calculator shows both so you can match whichever your system expects.
What is the Year 2038 problem?
Systems that store Unix time in a signed 32-bit integer can only count up to 2,147,483,647 seconds, which is reached at 03:14:07 UTC on 19 January 2038. Beyond that the value overflows. Modern systems use 64-bit integers, which postpone the limit by hundreds of billions of years.
Does Unix time account for time zones?
No. A Unix timestamp always refers to UTC. To display a local time you add the relevant UTC offset for the viewer's time zone. This calculator converts to and from UTC so the value is unambiguous; apply your own offset for local display.
Official sources
- The Open Group: POSIX definition of Seconds Since the Epoch.
- U.S. National Institute of Standards and Technology: Time and Frequency reference (UTC).
Reviewed by the CalculatorHub team, edited by James Graham, 16 June 2026. See our methodology.