Time reckoning by months seems to have been in familiar parlance among the Buddhist as we note the Buddha's using of the month as a time-unit when framing rules for the Order, such as those for the retention of gift-robes [Vin.iii,p 203,251,261]. Reference to any specific one of the months appears to have been in terms of their ordinal position, not in the year but in a given season [utu]. Thus it is usual to speak of 'the last month last month of the summer" [gimhanam pacchime mase, e.g., M..i, p. 79: S. iii,p.141, 155]; "the last month of the rains" [vassanam pacchime mase, e.g., D. ii, p.183, M.i.p.115; A.iv,p.102;v,p.22]; "the first month of the rains" [vassanassa pathame mase, e.g.,Vin. iv, p.117]; "while a month and a half of the summer remains" [diyaddhamasa seso gimhanati, e.g., Vin.iii,p252f.;iv,p117], "the first three months or the last three months" [purimam va temasam va temasam] of the rainy season' [Vin. i, p.138]. The tendency was to refer to any single season as a kind of quadruplet composed of consecutive months.
Nevertheless, there can be little doubt that the months were known to the Buddhist by their names, two of which are already referred to in the Vinaya, viz., Asalhi [Vin.i, p.137] and Kattika [Vin.iii, pp. 260, 262], and although there is no single location anywhere in the canonical literature where a full list of the twelve months occurs, it is rather unlikely that the names were unknown to the early Buddhist when by this time the Brahmanical contemporaries, with whom they undoubtedly came into contact, were quite familiar with them. Brahmanical astrological learning by this time has not only evolved a system of twenty-seven of twenty-eight lunar months, but also had adopted a selected number of them in naming the twelve months of their calendar. We know that, although the Buddha discouraged the practice of astrological forecasting for monks [D.i.p.10], he laid down a special emphasis on the importance of their studying the nakkhatta and that he even laid down a special rule in the Vinaya [Vin.ii,p.217] that forest-dwelling monks should learn the lunar mansion [nakkhattapadani]. Nuns were expected to consult the monks for the determination of uposatha days, etc., so that a monk would have inevitably found it a prerequisite of his calling to familiarise himself with the current astrological lore.This astrological lore could have been no other than the Brahamical systems, as there is absolutely no evidence of the Buddhist having had their own independent astrology. Occasional and incidental references to names of months other than Asalhi and Kattika but belonging the same system, for instance Citta, Savanna, Magha and Phagguna, are found in the early tradition of the Pali commentaries [KhpA. p.192.v, p.1068; SnA. ii, p. 456] which further supports this view. An added reason for suspecting the high probability is given by Tomas that several names of the months are found as proper names of personalities figuring in the earliest canonical literature.
It is, however, in the twelfth century Sri Lankan work, the Abhidhanappadipika, that we find a complete list. Here the names given, beginning with Citta [Caitra], correspond with one of the Hindu systems.
Buddhist months, with their Sanskrit equivalents