Question 1

What is a Unix timestamp?

Accepted Answer

A Unix timestamp (also called epoch time) is the number of seconds that have passed since January 1, 1970 at 00:00:00 UTC. It's a single number that represents a moment in time without needing a timezone attached, which is why computers use it internally for logs, databases, and APIs.

Question 2

Why does Unix time start on January 1, 1970?

Accepted Answer

1970 was chosen somewhat arbitrarily by early Unix developers as a convenient recent round date to count from. It stuck because so many systems were built on top of it, and changing the reference point now would break decades of software.

Question 3

What is the Year 2038 problem?

Accepted Answer

Many older systems store Unix time as a signed 32-bit integer, which can only count up to 2,147,483,647 seconds past the epoch. That limit is reached on January 19, 2038, at which point those systems can overflow and wrap back to 1901 unless they've been upgraded to 64-bit timestamps.

Question 4

How do I convert a Unix timestamp in Excel or Google Sheets?

Accepted Answer

In both Excel and Google Sheets, divide the timestamp by 86400 (seconds per day) and add it to the date serial number for January 1, 1970, then format the cell as a date-time. The formula is =A1/86400+DATE(1970,1,1), where A1 holds the timestamp in seconds.

Question 5

Is Unix time the same everywhere in the world?

Accepted Answer

Yes. A Unix timestamp refers to one specific instant regardless of where you are. Timezones only come into play when you convert that instant into a human-readable date and time, since the calendar date and clock time will differ by location.

Question 6

How do I know if a timestamp is in seconds or milliseconds?

Accepted Answer

Count the digits. Current Unix time in seconds has 10 digits, and won't reach 11 digits until the year 2286. In milliseconds it has 13 digits, in microseconds 16 digits, and in nanoseconds 19 digits. EpochKit detects this automatically.

Read time the way machines read it — and back again.

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