What this calculator does
Unix time counts the seconds elapsed since 1 January 1970 at midnight UTC. It is how most computer systems store a moment in time, because a single integer needs no timezone, no calendar rules and no formatting decisions, and comparing two of them is a subtraction.
The two numbers worth recognising are 0, which is the epoch itself, and 2,147,483,647, which is the largest value a signed 32-bit integer can hold. That one lands on 19 January 2038, and systems still storing timestamps in 32 bits will overflow at that moment, which is why the figure turns up in discussions of the 2038 problem.
The formula
A timestamp is converted by multiplying by 1,000 to get milliseconds and reading the result as a date, which is reported in UTC so it does not depend on where the page is being viewed. The reverse direction takes a date and reports the seconds since the epoch. The millisecond value is given separately because many programming environments, JavaScript among them, work in milliseconds rather than seconds.
| Term | Meaning |
|---|---|
| Epoch | The zero point of Unix time: 1 January 1970, 00:00:00 UTC. |
| Timestamp | Seconds elapsed since the epoch. Negative values represent dates before 1970. |
| UTC | Coordinated Universal Time, the reference the count is measured against, with no daylight saving. |
| 2038 problem | The overflow of signed 32-bit timestamps on 19 January 2038, after which the value wraps to a large negative number. |
The inputs explained
| Field | What to enter |
|---|---|
| Unix timestamp (seconds) | A Unix timestamp in seconds. If your value has 13 digits it is in milliseconds, so divide by 1,000 first. |
| …or a date to convert | A date to convert in the other direction, to seconds since the epoch. |
When to use it
Reading a timestamp from a log or database
Logs, APIs and database columns routinely store times as integers. Converting one to a readable date is the first step in working out when something actually happened.
Checking a token or cookie expiry
Expiry fields in tokens and cookies are usually Unix timestamps, and converting one shows whether it has passed and by how long.
Comparing two moments precisely
Subtracting two timestamps gives an exact difference in seconds with no timezone or daylight saving complications, which is why systems store time this way.
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
What dates do notable Unix timestamps fall on?
Five timestamps, from the epoch itself to the 32-bit limit.
| Timestamp | UTC date and time | In milliseconds |
|---|---|---|
| 0 | Thu, 01 Jan 1970 00:00:00 GMT | 0 |
| 1,000,000,000 | Sun, 09 Sep 2001 01:46:40 GMT | 1,000,000,000,000 |
| 1,700,000,000 | Tue, 14 Nov 2023 22:13:20 GMT | 1,700,000,000,000 |
| 2,000,000,000 | Wed, 18 May 2033 03:33:20 GMT | 2,000,000,000,000 |
| 2,147,483,647 | Tue, 19 Jan 2038 03:14:07 GMT | 2,147,483,647,000 |
Questions
Why does Unix time start in 1970?
It was a practical choice made by the early Unix developers, who needed a recent, round starting point. Nothing about the date is significant beyond being close to when the system was written and far enough back to cover the dates it needed to handle.
My timestamp has 13 digits rather than 10. What is it?
Milliseconds rather than seconds. JavaScript and several other environments count in milliseconds, so divide by 1,000 before entering it here. A 10-digit value is seconds and covers the range from 2001 to 2286.
Does Unix time account for leap seconds?
No, and this is a genuine subtlety. Unix time treats every day as exactly 86,400 seconds, so it does not count leap seconds. A leap second is absorbed by repeating or skipping a value rather than incrementing normally, which means Unix time is not a true count of elapsed SI seconds since 1970.
What happens in 2038?
Systems storing timestamps as signed 32-bit integers overflow on 19 January 2038 and wrap to a large negative value, reading as a date in 1901. Modern systems use 64-bit timestamps, which push the limit far beyond any practical horizon, but older embedded and legacy systems remain exposed.
For the weekday and week number of a converted date, see the day of the week calculator. For the gap between two dates in days, see the days between dates calculator.