What a Unix timestamp is
A Unix timestamp is a single number: the count of seconds since midnight UTC on 1 January 1970, a moment known as the epoch. Computers love it because comparing two instants becomes comparing two integers, and adding a day is just adding 86,400. People are less keen, because 1754912345 tells you nothing until you convert it, which is what this page is for.
Timestamps are always counted in UTC, so one value pins down the same instant everywhere on Earth. Your database in London and your server in Sydney can log the same timestamp and mean exactly the same moment; only the human-readable display changes with the time zone. That is why the converter shows both the UTC reading and your local time side by side. Everything runs in your browser, so the timestamps and logs you paste are never uploaded anywhere.
Worked examples
You can check the first one by hand: zero seconds after the epoch is the epoch. The second is a nice sanity test for any converter you do not trust yet, because the billionth second was widely celebrated and its date is easy to look up.
Seconds or milliseconds?
Two conventions coexist. Unix systems, most APIs and most databases count seconds, so current timestamps have 10 digits. JavaScript's Date.now(), Java and plenty of logging systems count milliseconds instead, giving 13-digit values. Paste the wrong flavour into a naive converter and your date lands either around the 1970s or tens of thousands of years in the future.
This tool detects the unit by size: anything of 100,000,000,000 or more is treated as milliseconds. The boundary is safe because 100 billion seconds would not arrive until around the year 5138, while 100 billion milliseconds was already back in March 1973. The detected unit is always shown in the results, and if you ever need to convert between the two by hand, multiply or divide by 1,000.
The year 2038 problem
Many older systems store timestamps as signed 32-bit integers, which top out at 2,147,483,647. That value corresponds to 03:14:07 UTC on Tuesday 19 January 2038. One second later the integer overflows and wraps negative, which the system reads as a date in December 1901. It is the same species of bug as the millennium bug, just baked into a binary format rather than a two-digit year.
Modern 64-bit operating systems already store time in 64-bit integers, which pushes the overflow roughly 292 billion years out, comfortably past the expected lifetime of the Sun. The risk sits with long-lived embedded devices, old file formats and databases with 32-bit timestamp columns, some of which will still be running in 2038. If you maintain anything in that category, testing it with the value 2,147,483,648 now is considerably cheaper than debugging it live on the day.
Frequently asked questions
What is the Unix epoch?
The epoch is midnight UTC on 1 January 1970, the zero point that Unix systems count from. A Unix timestamp is simply the number of seconds since that moment, which makes date arithmetic and comparisons trivial for computers even though the raw number means little to people.
How does the tool know whether I pasted seconds or milliseconds?
By size. Timestamps in seconds are currently 10 digits long, while millisecond timestamps are 13 digits. The tool treats any value of 100,000,000,000 or more as milliseconds, and it always tells you which unit it detected so you can override by dividing or multiplying by 1,000.
Do timestamps depend on my time zone?
No. A Unix timestamp identifies one exact instant everywhere on Earth, always counted in UTC. Time zones only affect how that instant is displayed, which is why this tool shows you both the UTC reading and the same moment in your local time.
What is the year 2038 problem?
Systems that store timestamps as signed 32-bit integers run out of room at 2,147,483,647, which lands at 03:14:07 UTC on 19 January 2038. One second later the value overflows and wraps to 1901. Modern 64-bit systems are unaffected, but old embedded devices and file formats can still be caught out.
Can a timestamp be negative?
Yes. Negative timestamps count backwards from the epoch, so they represent moments before 1 January 1970. For example, -86,400 is 31 December 1969 at midnight UTC. Many systems handle them correctly, but some tools and databases reject them, so test before relying on one.