Sed festival
Where the total number of regnal years for a given ruler is not known, Egyptologists have identified two indicators to deduce that total number: for the Old Kingdom, the number of cattle censuses; and for later periods, the celebration of a Sed festival. 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. The Sed festival was usually celebrated on the thirtieth anniversary of a pharaoh's ascension, and thus rulers who recorded celebrating one could be assumed to have ruled at least 30 years. However, once again, this may not have been standard practice in all cases.