The Ethiopian calendar (Amharic: የኢትዮጵያ ዘመን አቆጣጠር?; yä'Ityoṗṗya zämän aḳoṭaṭär) is the principal calendar used in Ethiopia and also serves as the liturgical year for Christians in Eritrea and Ethiopia belonging to the Orthodox Tewahedo churches, Eastern Catholic Churches and Coptic Orthodox Church of Alexandria. It is a solar calendar (the older Alexandrian or Coptic calendar brought to Ethiopia by missionaries) which in turn derives from the Egyptian calendar, but like the Julian calendar, it adds a leap day every four years without exception, and begins the year on August 29 or August 30 in the Julian calendar. A seven- to eight-year gap between the Ethiopian and Gregorian calendars results from an alternate calculation in determining the date of the Annunciation.
Like the Coptic calendar, the Ethiopic calendar has twelve months of 30 days plus five or six epagomenal days, which comprise a thirteenth month. The Ethiopian months begin on the same days as those of the Coptic calendar, but their names are in Ge'ez. The sixth epagomenal day is added every four years without exception on August 29 of the Julian calendar, six months before the Julian leap day. Thus the first day of the Ethiopian year, 1 Mäskäräm, for years between 1900 and 2099 (inclusive), is usually September 11 (Gregorian). It, however, falls on September 12 in years before the Gregorian leap year.
In the Gregorian year 2015, the Ethiopian calendar year 2008 begins on September 12, rather than September 11, on account of this additional epagomenal day occurring every four years.