From Wikipedia

Great Pharaohs

3150 BC - 1351 BC

The creation of a reliable chronology of Ancient Egypt is a task fraught with problems. While the overwhelming majority of Egyptologists agree on the outline and many of the details of a common chronology, disagreements either individually or in groups have resulted in a variety of dates offered for rulers and events. This variation begins with only a few years in the Late Period, gradually growing to a decade at the beginning of the New Kingdom, and eventually to as much as a century by the start of the Old Kingdom.

The "Conventional Egyptian chronology" is the scholarly consensus, placing the beginning of the Middle Kingdom in the 21st century BC. Scholarly consensus regarding the beginning of the Old Kingdom has shifted to earlier dates during the 20th century and is now placed in the 27th century BC.