Coptic (Alexandrian) Calendar
The Coptic year starts on Gregorian calendar date September 11 (in non-leap years) and has 3 seasons divided into 4 months each (30 days per month) plus a 13th month at the end of the year with 5 days (6 days on leap years).
Based on the ancient Egyptian calendar, the Coptic calendar is still used in Egypt and by the Coptic Orthodox Church and other churches as a liturgical calendar.