How to convert a Unix timestamp
- Check the live clock at the top for the current Unix time.
- Paste a timestamp in seconds or milliseconds to see it as a date.
- Read it in UK time, UTC and ISO 8601 format.
- To go the other way, pick a date and time and copy the timestamp.
What Unix time is
Unix time counts the seconds since midnight UTC on 1 January 1970, a starting point known as the epoch. It is one plain number with no time zones or date formats, which makes it easy for computers to store, sort and compare. Databases, log files and APIs use it widely.
Unix time ignores leap seconds. Every day is treated as exactly 86,400 seconds, so the count lines up with calendar dates but can differ by a few seconds from a strict count of elapsed time.
Many systems, including JavaScript, use milliseconds instead. A timestamp in seconds for a present day date has 10 digits, while one in milliseconds has 13. This converter tells them apart automatically, so you do not get a date in 1970 or thousands of years ahead.
British Summer Time pitfalls
A timestamp is the same moment everywhere in the world. Only the way it is displayed changes. In winter UK time matches UTC, but during British Summer Time, from the last Sunday in March to the last Sunday in October, UK clocks are an hour ahead.
This catches people out when a report shows 09:00 UTC and they read it as 9am in London in July, when it was really 10am. Showing both UK time and UTC side by side, as this tool does, helps. Be careful around the clock changes too: in October one hour of UK local time happens twice, so a local time alone can be ambiguous.
The year 2038 problem
Older systems store Unix time as a signed 32 bit number, which runs out at 2,147,483,647. That is 03:14:07 UTC on 19 January 2038. One second later, such a counter wraps round to a negative number, read as a date in December 1901. Most modern systems use 64 bit time and are not affected, but older embedded devices and software can be.
Questions people ask
Is a Unix timestamp in UTC?
Yes. It always counts from midnight UTC on 1 January 1970, regardless of where the computer is. Time zones only matter when you display it.
How can I tell if a timestamp is in seconds or milliseconds?
For current dates, 10 digits means seconds and 13 digits means milliseconds. The converter detects this for you.
What is ISO 8601?
An international date format such as 2026-10-05T14:30:00Z. It sorts correctly as text and avoids confusion between UK and US date orders.
Can a Unix timestamp be negative?
Yes. A negative number is a date before 1 January 1970.
Does the converter handle British Summer Time?
Yes. UK time is shown as GMT or BST depending on the date, and UTC is shown alongside it.