Last update: Oct 20 2019 07:04:50

Unix time (also known as POSIX time or UNIX Epoch time) is a system for describing a point in time, defined as the number of seconds that have elapsed since 00:00:00 Coordinated Universal Time (UTC), Thursday, 1 January 1970, minus the number of leap seconds that have taken place since then. It is used widely in Unix-like and many other operating systems and file formats.

On systems where the representation of Unix time is as a signed 32-bit number, the representation will end after the completion of 2,147,483,647 (231 - 1) seconds from 00:00:00 on 1 January 1970 minus the number of leap seconds that have taken place since then, which will happen on 19 January, 2038 03:14:08 UTC. This is referred to as the "Year 2038 problem" where the 32-bit signed Unix time will overflow and will take the actual count to negative.

Converting a date and time into an epoch value makes it much easier to find the difference, add, and subtract from a time value. For example, you could convert the time to an epoch and subtract it from another epoch value to quickly determine the difference. If the difference was 176,400 and you used the above chart or a math formula to find the difference is 2 days and 1 hour (86400 + 86400 + 3600 = 176,400).