Ancient

Until the 4th century BC, the beginning of the months of the lunar calendar were based on observation,^[19] beginning at dawn on the morning when a waning crescent moon could no longer be seen.^[20] The intercalary month was added every few years as needed to maintain the heliacal rising of Sirius within the month.^[21] According to the civil calendar, the month fell in order with the rest regardless of the state of the moon. It always consisted of 30 days, each individually named and devoted to a particular patron deity, and was always followed by an intercalary month, although it slowly cycled relative to the solar year and Gregorian date owing to the lack of leap days until the Ptolemaic and Roman eras.

Torches were ritually carried on the 28th day of the month in preparation for the spiritual danger of the intercalary month that followed.^[22]

New Year's Eve (Msy or Msyt) was observed on the 30th day of the month.^[13]

Once the holidays were transferred to the civil calendar, Wep Renpet proper was celebrated on the first day of Thoth^[6] by at least the Middle Kingdom,^[23] though the last month of the year continued to bear its name. The holiday honored the birth and youth of the personification of the sun and its fight against evil. Royal artisans were freed from work,^{[6][lower-alpha 5]} temples lit torches to banish darkness and its demons, spells concerning the crushing of enemies were cast, and ritual combat occurred during a "water procession" on temple lakes.^[10] People threw ink into water, cleansed themselves, and painted their eyes green.^[22] It was a common occasion for pharaonic coronations during the Middle Kingdom and the occasion of ceremonies of renewed kingship in other eras, occasioning his officials to present him with new year's gifts.^[10] This practice extended to commoners presenting gifts—such as rings, scarabs, and bottles inscribed "Happy New Year's" (Wpt Rnpt Nfrt)—to one another during the Saite Period.^[26]

In Ptolemaic Egypt, the festivities began on the last day of Mesori and ran through the first nine days of Thoth.^[23]

Coptic

In the present-day Coptic calendar, Mesori has fallen between August 7 and September 5^[14] since AD 1900 (AM 1616)^[27] and will continue to do so until AD 2100 (AM 1816).^[28] In that year, the Gregorian calendar's lack of a leap day will cause the Coptic month to advance another day relative to it^[29] and it will run from August 8 to September 6. The Coptic liturgical calendar of the month consists of:^[30]