What is the relationship between the Coptic calendar and the ancient Egyptian calendar?

Ancient Egyptians developed their calendar at least as far back as 4240 B. C. The famous Greek historian Herodotus remarks that the Egyptians preceded the Greeks in correcting their calendar by adding an additional five days each year to the standard twelve months of thirty days each.⁶³²

The Copts inherited an interest in the solar calendar from their ancestors, the Pharaohs, and until today, even illiterate Copts in Egypt still follow and pass on their oral traditions for the reckoning of times, by which they order the agricultural seasons, predict weather conditions, and worship using the liturgical calendar.

The Coptic year, which is of ancient Egyptian origin, is divided into twelve months, each of which contains thirty days, and to which are added five extra days at the end of the year called the “little month” or the Epagomenal days. Every four years, in a leap year, six days are added instead of five. The year is divided into three seasons with each season made up of four months. The first season is the season of the flooding of the Nile; the second is the season for sowing; and the third is the season for harvesting and gathering fruits. This seasonal structure continues to define the Coptic liturgical year in Egypt. It was also used outside of Egypt until the Holy Synod of the Coptic Church issued a decree to combine the prayers of the three seasons into a single unified litany of the air of the heaven, the fruits of the earth, and the waters of the rivers together, since in the diaspora, each land has its own agricultural conditions that are unlike those of Egypt.