/01 The three time jobs, in one place
Work with time long enough and the same three jobs keep coming back. Converting timestamps: turning an unreadable number from a log file into a date a human recognises, or turning a date back into that number. Date arithmetic: adding or subtracting days, weeks, or hours from a date, the maths behind every deadline and countdown. And time zones: the same moment shown in several places at once, for scheduling anything across regions.
This tool does all three. Paste a Unix timestamp and read the date in seconds, milliseconds, ISO format, and plain language. Add or subtract an interval from any date and see the result immediately. Show one moment in up to six time zones side by side, each with its UTC offset.
The value of having them together is that real questions usually need more than one. A timestamp from a server, the deadline it relates to, and the time that lands in your colleague's calendar in another country: three jobs, one page.
/02 What a Unix timestamp is and why it exists
A Unix timestamp counts the seconds since the start of 1970, in UTC, with no time zone, no daylight saving, and no local variation. It is the standard way computers store a moment in time, and it is completely unambiguous: the same number means the same instant everywhere on earth.
It is also unreadable. 1704067200 tells you nothing unless you convert it, which is the job of the converter here. Paste the number, choose seconds or milliseconds, and the readable date appears, along with the ISO format that APIs use and the plain language version for emails and notes.
The direction reverses too. Need to hardcode a launch moment into a script, or set an expiry date in a system that wants a timestamp? Type the date and read the number back out.
/03 Where date arithmetic goes wrong
Adding and subtracting dates sounds simple, and two details trip everyone. First, a local day is not always 24 hours. When daylight saving starts or ends, one day a year is 23 hours and another is 25, so adding 86,400 seconds is not always the same as adding one day. Working in UTC avoids the problem, and it is why serious systems store and calculate in UTC and convert to local time only for display.
Second, time zone offsets are not all whole hours. India sits at 5 hours 30 minutes from UTC. Nepal sits at 5 hours 45. Parts of Australia use half-hour offsets. Half the world's population lives at an offset that would surprise you if you assumed whole hours, and a meeting time worked out on that assumption lands wrong.
The date maths here handles both details properly, using the zone rules in force on the date you enter, not the rules in force today.
/04 Timestamps that land in 1970 or far future
There is one bug so common it deserves its own mention. A timestamp shows as 1970, or as a date tens of thousands of years in the future, and the reason is nearly always the unit. JavaScript uses milliseconds. Most other systems use seconds. A milliseconds value read as seconds lands near the present; a seconds value read as milliseconds lands close to 1970, the epoch itself.
The numbers make it easy to tell them apart. A current Unix timestamp in seconds is ten digits. The same moment in milliseconds is thirteen. Count the digits before you paste, or just try both fields: the correct one reads as a sensible date and the wrong one reads as absurdity.
This tool gives seconds and milliseconds separate fields precisely so the check takes no thought. Whichever field produces a sane date is the unit your value was in, and now you know which one your system is speaking.
/05 Unix timestamp converter: seconds, milliseconds and ISO 8601
The most common mistake when converting a Unix timestamp is mixing up seconds and milliseconds. Unix time is traditionally counted in seconds since 1 January 1970 UTC, so right now it is a 10-digit number. JavaScript's Date.now() and many APIs count in milliseconds instead, giving a 13-digit number. Treat a millisecond value as seconds and you land tens of thousands of years in the future; treat seconds as milliseconds and you land in January 1970.
This Unix timestamp converter handles both formats and ISO 8601, the readable 2024-01-01T00:00:00.000Z style used in JSON and logs. Epoch converter and Unix timestamp converter are two names for the same job, so whichever one you searched for, paste the value in and read the date in UTC and your local time.