The ancient civil Egyptian calendar had a year that was 365 days long and was divided into 12 months of 30 days each, plus five extra days (epagomenae, from Greek ἐπαγόμεναι) at the end of the year. The months were divided into three weeks of ten days each. Because the ancient Egyptian year was almost a quarter of a day shorter than the solar year and stellar events therefore "wandered" through the calendar, it has been referred to as the annus vagus, or "wandering year".

Based on his understanding of the Palermo Stone, Alexander Scharff believed that the Old Kingdom period observed a year with 320 days.