What a Unix timestamp is
Computers keep time by counting. A Unix timestamp (also called epoch time or POSIX time) is the number of seconds that have passed since 00:00:00 UTC on 1 January 1970 — the "epoch". Every moment since has a single number: the moment this standard was already old, 1,000,000,000, fell on 9 September 2001; 1,700,000,000 fell on 14 November 2023 at 22:13:20 UTC (try it above — it is a handy test value). Counting seconds from a fixed point turns messy calendar arithmetic into subtraction: the distance between two moments is just the difference of their timestamps, with no months, leap years or time zones to argue about. The calendar only re-enters when a human needs to read the result — which is exactly the moment this converter exists for. Timestamp 0 is the epoch itself: 1970-01-01 00:00:00 UTC.
Seconds or milliseconds? This converter takes both
The one trap in the whole system is units. The classic Unix timestamp counts seconds and currently has 10 digits. JavaScript, and many APIs that imitate it, count milliseconds — the same instant written 1,000 times larger, a 13-digit number. Paste a millisecond value into a seconds-only converter and it cheerfully reports a date tens of thousands of years in the future; paste seconds where milliseconds are expected and everything happens within a day of the epoch. This converter removes the guesswork: values of 1 trillion (1,000,000,000,000) or more are treated as milliseconds, everything smaller as seconds, and the reverse direction shows both forms so you can copy the one your system expects. The live counter at the top of the tool shows the current time in seconds, ticking once per second — a quick reality check for whatever system you are debugging.
Reading the results: UTC and local time
A timestamp does not include a time zone — it names one worldwide instant. The date it becomes depends on where you stand, which is why the result here shows the moment three ways: as a plain UTC date and time (the headline figure), in full UTC (GMT) wording, and in your local time as set on your device. When converting in the other direction, the date-and-time picker is read as your local time, so the timestamp you get is the one for that wall-clock moment where you are. Most confusion in real systems is not the epoch math but a silent time-zone assumption somewhere in the chain — comparing the UTC and local lines here is the fastest way to spot an offset of exactly a few hours, which is the fingerprint of a time-zone bug. One footnote for the far-sighted: systems storing timestamps as signed 32-bit integers run out in January 2038 (the "Year 2038 problem"); anything modern uses 64-bit values and will outlast all of us.
Frequently asked questions
What date is timestamp 0?
The epoch itself: Thursday, 1 January 1970 at 00:00:00 UTC. Enter 0 above to see it. Negative timestamps count backwards from the epoch into 1969 and earlier.
How can I tell if a timestamp is in seconds or milliseconds?
Count the digits. A current seconds timestamp has 10 digits (around 1.7–1.8 billion); the same moment in milliseconds has 13 digits. This converter accepts both and detects milliseconds automatically at 1 trillion and above.
Which time zone does the date-to-timestamp direction use?
Your device's local time zone: the date and time you pick are interpreted as your wall-clock time, and the resulting timestamp is that instant. The timestamp-to-date direction shows both the UTC moment and your local equivalent so you can compare.
Why is the date I got off by exactly a few hours — or 1,000×?
Hours off means a time-zone assumption differs somewhere — the value was probably recorded in UTC and read as local, or the reverse. A wildly wrong date (year 1970 or the year 56000+) means seconds and milliseconds were mixed up. Both are classic, and both are why this page shows every interpretation at once.
Private by design: this converter runs entirely in your browser. The timestamps and dates you enter are never uploaded, stored or shared.