The Coptic calendar, sometimes referred to as the Alexandrian Calendar, is based on the ancient Egyptian calendar of the solar year. This calendar system continued to be used by the Coptic Church. The Coptic year is divided into 12 months of 30 days each, followed by five more days, called epagomenai, as well as the extra day of an intercalary month, making a year of 366 days. The Coptic leap year follows the same rules as the Julian calendar so that the extra month always has six days in the year before a Julian leap.
Since the fourth century, Coptic years are counted according to the Era of Diocletian, whose accession to the throne in 284 marks the beginning of “Era of Martyrs” or Coptic calendar because of the mass execution of Christians and the martyrdom of countless believers. It is conventionally abbreviated A. M. (for anno martyrum). Thus the Copts mark the 29 August 284 A.D. as the beginning of their history.
The Coptic year starts on 11/12 September, depending on leap years. The twelve months, pronounced in Arabic, are: Tut (11/12 September to 9/10 October), Babah (11/12 October to 9/10 November), Hatur (10/11 November to 9/10 December), Kiyahk (10/11 December to 8/9 January), Tubah (9/10 January to 7/8 February), Amshir (8/9 February to 9 March), Baramhat (10/11 March to 8 April), Baramudah (9 April to 8 May), Bachans (9 May to June 7), Ba’unah (8 June to 7 July), Abib (8 July to 6 August), and Misra (7 August to 5 September). The epagomenal or intercalary days are called in Arabic “al-Nasi.”
The three seasons of the Coptic calendar are based on the ancient Egyptian three seasons of the agricultural life in the Nile valley: The Nile-flood season, the sowing season, and the harvest season. Although the agricultural system was completely changed after the erection of the High Dam of Aswan, these seasons are still remembered in the liturgy of the Coptic Church; for example “Priest: Graciously, O lord, bless the waters of the river, the vegetation, the plants of the fields, the winds of the sky, and the crops of the land this year. . . .”