Ethiopian country has its own ancient calendar that is has always been using since then to date. The Ethiopian calendar is quite similar to the Julian calendar, which was the predecessor to the Gregorian calendar most countries use today.
The Ethiopian Calendar has more in common with the Coptic Egyptian Calendar. The Ethiopic and Coptic calendars have 13 months, 12 of 30 days each and an intercalary month at the end of the year of 5 or 6 days depending whether the year is a leap year or not.

The Ethiopian calendar is much more similar to the Egyptian Coptic calendar having a year of 13 months, 365 days and 366 days in a leap year (every fourth year) and it is much influenced by the Ethiopian Orthodox Tewahedo Church, which follows its ancient calendar rules and beliefs. The year starts on 11 September in the Gregorian Calendar or on the 12th in (Gregorian) Leap Years. The Coptic Leap Year follows the same rules as the Gregorian so that the extra month always has 6 days in a Gregorian Leap Year.

However, the Ethiopian Calendar differs from both the Coptic and the Julian calendars.
The difference between the Ethiopic and Coptic is 276 years. In spite of this, the Ethiopic Calendar is closely associated with the rules and the different calculations influenced by the Coptic Church and the Ethiopian Orthodox Tewahido Church.
Based upon the ancient Coptic Calendar, the Ethiopian Calendar is seven to eight years behind the Gregorian Calendar, owing to alternate calculations in determining the date of the annunciation of the birth of Jesus.

The Coptic New Year is a holiday in Ethiopia. Christmas falls on the 7th of January as in the Orthodox “old” calendar. Likewise, Epiphany is on the 19th of January. Easter would appear to be calculated according to the Orthodox calendar also.
Christmas 🎄 and Epiphany also do not appear to move by one day during Leap Years as they would if they were being set by the above calendar. Thus, it would seem that Christian feasts are set according to the Orthodox calendar rather than according to the Coptic. An Egyptian Coptic source simply describes the date of Easter as being “the second Sunday after the first full moon in Spring.”
IMG_20171102_202823_646-254x365 Ethiopian Calendar 2018, Date and Time