These additional days were considered to be very unlucky or unpropitious. Both of them observe three 365 day years followed by one 366 day year. It consists of twelve 30-day months with five "gatha days" added at the end of the year.
Two eastern Mediterranean peoples who did not embrace Islam were early Christians in upper Egypt, whom we now call Copts, and their neighbors to the south, the Ethiopians. Their years are divided into 12 months of 30 days each, and the extra five or six days are added after the twelfth month. Each of the thirty days as well as each of the gatha days has its own name.
By observing the movement of Sirius, Egyptians came to grips with the fact that the year was more than five days longer than their venerable 360-day calendar.
It contained twelve months of 30 days each and an extra five days at the year’s end.
Every fourth year an additional day for a total of six days were added at the end of the year.
Instead, they returned to a fixed-length calendar that had 12 months of 30 days each, but with five days added at the end.
10 Usually at a date later than the mid-eighth century B. E., many other peoples who had previously considered the year to be 360 days in length reluctantly returned to a calendar of twelve 30-day months, but added five days to the end of their year. with the birth of their founder, the prophet Zoroaster, use a calendar of 365 days.