Egyptian chronology: why dates differ between books
Why one book dates Khufu to 2589 BC and another to 2551, and how the grades work.
A reader who compares two books may find that Hatshepsut starts in 1479 BC in one and 1473 BC in the other, and that Khufu's reign moves by forty years. This is not an error in either book. It comes from how the dates are put together.
Three kinds of evidence
The first is the king lists, which give the order of rulers and often their reign lengths, but not absolute dates. They sometimes leave kings out and sometimes contradict one another. The second is astronomy. A few texts record the rising of the star Sirius on a known day, and from that a year can be calculated within a narrow window. The third is radiocarbon dating of short-lived material from known reigns, which has narrowed the earlier periods considerably.
Where the doubt grows
The New Kingdom is anchored by astronomy and is fairly good, with an uncertainty of a few years. The Middle Kingdom depends on a Sirius record from the reign of Senusret III, whose observing place is argued over, and this gives the "high", "middle" and "low" chronologies, which differ by decades. The Old Kingdom and earlier rely on reign lengths added up from fragmentary lists, so errors build up, and the date of Khufu's accession is uncertain by about forty years.
Co-regencies
A king sometimes ruled with a successor for a time. If a book counts the shared years twice, the total is too long. Amenemhat I and Senusret I are a clear case. Where scholars disagree, this site follows a conventional chronology and shows the range.
How this site grades dates
Each ruler has a start and end year with a minimum and maximum, and a grade. A means within a few years. B within about a decade. C within about a century. D means the order or even the existence of the ruler is disputed. At present 57 rulers score A, 102 score B, 53 score C and 12 score D. On the Reign Roll, the red bracket on a selected bar shows how far its start could move.