How to use the Unix Timestamp Converter
- Choose whether you are converting a timestamp to a date or a date to a timestamp.
- Paste the timestamp in seconds, or pick the date.
- Read the UTC date and time, given in ISO order.
- Copy the milliseconds value when working with JavaScript, which uses that unit.
- Copy the ISO 8601 string for APIs and log files.
How the calculation works
Unix time counts the seconds elapsed since midnight UTC on 1 January 1970, the epoch. It is the near-universal internal representation of time in computing because it is a single integer with no time zone, no locale and no formatting ambiguity — every complication is deferred to the display layer, where it belongs.
The most common practical error is a unit mismatch. Unix time is conventionally in seconds, but JavaScript, Java and many APIs use milliseconds, and some systems use microseconds. A timestamp that resolves to 1970 almost always means milliseconds were read as seconds; one that lands 50,000 years in the future means the reverse. Checking the digit count is the quickest diagnostic: ten digits is seconds, thirteen is milliseconds.
Unix time deliberately ignores leap seconds, treating every day as exactly 86,400 seconds. That makes arithmetic simple but means it is not a true count of elapsed SI seconds since 1970 — it currently runs a few dozen seconds ahead of that. For everything short of precision timing and astronomy the difference is irrelevant, but it is worth knowing that the abstraction has a seam.
timestamp = (UTC milliseconds since 1970-01-01) / 1000; date = new Date(timestamp × 1000)Source: POSIX.1-2017 definition of seconds since the Epoch; ISO 8601-1:2019 for the string format.
Worked example
A log entry records the timestamp 1798761600 and needs converting for an incident report.
- Ten digits, so the value is in seconds, not milliseconds.
- Convert: 1798761600 × 1000 = 1,798,761,600,000 ms.
- That resolves to 2027-01-01 00:00:00 UTC.
- In New York (UTC−5) the same instant is 31 December 2026 at 19:00.
1 January 2027 00:00 UTC — and note the local date is the previous day in the Americas, which matters when an incident window is reported.
Frequently asked questions
Seconds or milliseconds?+
Count the digits. Ten digits is seconds for current dates; thirteen is milliseconds. Getting it wrong shifts the result by a factor of a thousand.
What is the year 2038 problem?+
A signed 32-bit timestamp overflows on 19 January 2038. Modern systems use 64-bit values, which last far beyond the age of the universe.
Can a timestamp be negative?+
Yes — negative values represent dates before 1970. Some older systems reject them, which is a common source of bugs with historical dates.
Does Unix time include leap seconds?+
No. Every day is treated as exactly 86,400 seconds, so it is a calendar count rather than a true elapsed-second count.
Last reviewed August 31, 2026. We review this page whenever the underlying formula, tax year, published rate or standard changes.