Το '''Αιθιοπικό''' ημερολόγιο is the principal calendar used in [[Ethiopia]] and is also the [[liturgical]] year of christians in Eritrea belonging to the [[Eritrean Orthodox Tewahdo Church]], [[Eastern Catholic Church]] of Eritrea and [[Lutheran]] (Evangelical Church of Eritrea), where it is commonly known as the '''Ge'ez calendar.''' It is based on the older Alexandrian or [[Coptic calendar]], which is based on the even older [[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.
Like the Coptic calendar, the Ethiopian/Ge'ez calendar has twelve months of 30 days each plus five or six [[epagomenal]] days (usually called a thirteenth month). Furthermore, its months begin on the same days as those of the Coptic calendar, but they have different names, that are in [[Ge'ez language|Ge'ez]]. The sixth epagomenal day is added every four years without exception on August 29 in the Julian calendar, six months before the Julian leap day. Thus the first day of the Ethiopian/Ge'ez year, 1 Mäskäräm, for years between [] and 2099 (inclusive), is usually [[September 11]] ([[Gregorian Calendar|Gregorian]]), but falls on [[September 12]] (Gregorian), in years before the Gregorian leap year.