There were two different types of calendars used throughout their time.
The Egyptian Lunar Calendar had 345 days, 12 lunar months, that were divided into three seasons. Each season had 4 calendar months. It is called a lunar calendar because it is based on the cycle of the moon.
The second type of calendar was the Egyptian Solar Calendar. It is dated back to the 3rd Millennium B.C. (the Early Middle Bronze Age). One weeks consisted of 10 days. One month was 3 weeks (30 days). Four months was one season (120 days). The three seasons (360 days) plus 5 holy days, made the calendar 365 days long. There were 5 holy days added at the end of the year.
The 5 holy days were dedicated to:
Osiris God of the Dead
Isis Goddess of motherhood, magic and fertility
Horus God of the King and Vengeance
Seth God of Desert, Storms, and Foreigners
Nephthys Goddess Lamentation
Full Credit for Calendar Information: http://www.king-tut.org.uk/ancient-egyptians/ancient-egyptian-calendar.htm