The Egyptian calendar was based of a year of 365 days, with twelve months and three seasons. Each month had three ten-day weeks, for a total of 30 days. The last five days of the year corresponded to the birthdays of five deities: Osiris, Isis, Horus, Seth and Nephthys. Since the Egyptians did not take leap years into account, their calendar got further and further away from the seasons. This meant that at one point, the summer months actually fell in winter. Only every 1,460 years did their calendar year synchronize with the seasonal year.
The three seasons corresponded to the cycle of the Nile and agriculture. New Year's day was on July 19 (in the Julian calendar) and marked the beginning of the first season, akhet. This was the time of the flooding of the Nile. The next season, during which the crops began to emerge, was called peret and started on November 16. The last season, Shemu, began on March 17 at harvest time. The last five days of the year, corresponding to the birthdays of the deities, were July 14 to 18, days which were considered unlucky and dangerous.
Besides the civic calendar, there was a religious calendar that marked the festivals and ceremonies associated with particular deities and temples. This calendar was based on a 29.5-day month, which made it more accurate according to the phases of agriculture and the astronomical cycle of the stars.