Not knowing whether monarchies were simultaneous or sequential results in widely differing chronological interpretations.
Where the total number of regnal years for a given ruler is not known, Egyptologists have identified two indicators to provide that total number: for the Old Kingdom, the number of cattle censuses; and for later periods, the celebration of a sed festival.
The majority of Egyptologists agree on the outline and many details of the chronology of Ancient Egypt.
This scholarly consensus is the so-called Conventional Egyptian chronology, which places the beginning of the Old Kingdom in the 27th century BC, the beginning of the Middle Kingdom in the 21st century BC and the beginning of the New Kingdom in the mid-16th century BC.
The disparities between the two sets of dates result from additional discoveries and refined understanding of the still very incomplete source evidence.A number of Old Kingdom inscriptions allude to a periodic census of cattle, which experts at first believed took place every second year; thus records of as many as 24 cattle censuses indicate Sneferu had reigned 48 years.However, further research has shown that these censuses were sometimes taken in consecutive years, or after two or more years had passed.In the 20th century, such biblical bias has mostly been confined to alternative chronologies outside scholarly mainstream.A useful way to work around these gaps in knowledge is to find chronological synchronisms, which can lead to a precise date.Despite this consensus, disagreements remain within the scholarly community, resulting in variant chronologies diverging by about 300 years for the Early Dynastic Period, up to 30 years in the New Kingdom, and a few years in the Late Period.