P. Monts.Roca inv. 314 contains the only Demotic monthly almanac attested so far. It preserves a section of two columns that record the movement of the planets for two consecutive years (Venus and a hint of Mercury in column 1, and Jupiter and Mars in column 2), indicating month, day, zodiac sign, longitude in degrees and minutes, and synodic phenomena if present. From the analysis of the information recorded I propose a dating of the data to the years 71–73 CE. The table contains the first evidence for the designation of synodic phenomena in Demotic, and allows for the proposal of an interpretation of the origin of the sign for first and last visibility used in Greek papyri. It also contains evidence for a secondary use of the sign for zero, attested in Babylonian astronomical texts as well. P. Monts. Roca inv. 314 thus provides further evidence for the transmission of astronomical knowledge from Mesopotamia to the Greek world through the mediation of Egypt.