How the Ethiopian calendar works
Each of the first twelve months, from Meskerem to Nehase, has exactly 30 days. Pagume follows with 5 days, or 6 in a leap year, making 365 or 366 days. A leap year comes every fourth year without exception, in the year before a Julian leap year, so the calendar keeps step with the Julian calendar rather than the Gregorian one. That is why Ethiopian New Year moves between 11 and 12 September on the Gregorian calendar. The Ethiopian year count, Amete Mihret (Year of Mercy), is seven years behind the Gregorian count from September to December and eight years behind from January to September.
The Coptic calendar
The Coptic calendar has the same structure: twelve 30-day months, Thout to Mesori, and a short month called Nasie or Pi Kogi Enavot. Its months begin on the same days as the Ethiopian months; only the names and the year count differ. Coptic years are counted from 284 CE, the Era of the Martyrs, so Coptic year numbers are 276 lower than Ethiopian ones. Arabic month names such as توت and بابه are used in Egypt, where some are also familiar from the agricultural year.
Ethiopian Orthodox holidays in this tool
Enkutatash, the New Year, is 1 Meskerem. Meskel, the Finding of the True Cross, is 17 Meskerem, usually 27 September. Genna, Christmas, is 29 Tahsas in the years of Matthew, Mark and Luke, and 28 Tahsas in the year of John, as the Ethiopian Orthodox Tewahedo Church Sunday School Department describes it, which keeps it on 7 January. Timkat, Epiphany, is 11 Tir, usually 19 January. Fasika, Easter, follows the Orthodox Easter calculation. Eves, fasting periods and local celebrations differ, so your church will announce the details.
The four evangelist years
Ethiopian years are named in a repeating cycle after the four evangelists: the Year of Matthew, then Mark, then Luke, then John. The Year of Luke is the leap year, when Pagume has six days. The tool shows the evangelist year with every converted date, because some dates in the church calendar depend on it.
How the dates were checked
The conversion is plain arithmetic from each calendar's starting date. It was compared with the Ethiopian and Coptic calendars built into modern browsers for every day from 1900 to 2100, in both directions, with no differences, and against published New Year dates such as 11 September 2005 and 12 September 2007. Dates are calendar days and are not affected by your time zone. In Ethiopia the day is often counted from 6 in the morning, a different clock from the calendar date shown here. This is general help, not religious guidance; for church services and fasting, ask your own priest or parish.