Overview#MacOS Epoch is midnight beginning January 1 1904 Coordinated Universal Time (UTC)
January 1, 1904, was chosen as the base for the Macintosh clock because it was the first leap year of the twentieth century. 1900 wasn't a leap year because leap years are skipped every 100 years for three centuries. On the fourth century, which will be the year 2000, the leap year isn't skipped. This means that by starting with 1904, Macintosh system programmers could save a half dozen instructions in their leap-year checking code, which they thought was way cool.