Guide · Updated 2026-10-08
Unix Timestamps Explained: Seconds, Milliseconds and Time Zones
What a Unix timestamp is, how to tell seconds from milliseconds, how to convert one to a date, and why time zones cause most of the confusion.
A Unix timestamp is a single number that stands for a moment in time: the number of seconds since midnight UTC on 1 January 1970. Systems like it because it has no time zone and sorts correctly. The Unix Timestamp Converter turns one into a readable date and back.
A worked example
The timestamp 1700000000 is Tuesday 14 November 2023 at 22:13:20 UTC. Its ISO 8601 form is 2023-11-14T22:13:20.000Z, and in milliseconds it is 1700000000000. The same moment shows as 22:13 in the UK in November, because the UK is on UTC in winter, and as 23:13 in central Europe.
Seconds or milliseconds?
| Digits | Usually | Example |
|---|---|---|
| 10 | Seconds | 1700000000 |
| 13 | Milliseconds | 1700000000000 |
JavaScript and many web tools use milliseconds, while most databases and command-line tools use seconds. If a converted date lands in 1970 you probably gave milliseconds where seconds were expected, and if it lands thousands of years ahead, the reverse.
Dates to timestamps
You can also type a date. “2026-01-01 12:00” is read in your device’s time zone. When tested in the UK in winter, it gave 1767268800, the same as noon UTC. In summer, or in another country, the same text gives a different number, because the time zone is part of the question.
The time zone trap
- The timestamp itself has no time zone. Only the display does.
- “Midnight” differs between places, so store timestamps and convert them for display.
- Daylight saving makes some local times appear twice or not at all, which is why a log in local time can look out of order.
Related calculations
To count the days between two dates use the Date Difference Calculator, which counts working days from the start date up to but not including the end date. To move a date forward or back use Add or Subtract Days. Adding one month to 31 January gives 3 March, because February has no 31st, so check month-end results.
The year 2038 problem
Systems that store the timestamp as a signed 32-bit number run out on 19 January 2038. Modern systems use 64 bits, but old devices and software can still be affected.
Frequently asked questions
What is timestamp 0? 1 January 1970, 00:00:00 UTC.
Why is my converted time an hour out? Usually daylight saving: the display uses your device’s time zone.