The calendar traditionally used in medieval Armenia was based on an invariant year length of 365 days. As a result, the correspondence between it and both the solar year and the Julian calendar slowly drifted over time, shifting across a year of the Julian calendar once in 1,461 calendar years (see Sothic cycle). Thus, the Armenian year 1461 (Gregorian 2010/2011) completed the first full cycle; Armenian year 1 began on 11 July 552 of the Julian calendar, and Armenian year 1462 began on 24 July 2012 of the Gregorian calendar (corresponding to Julian 11 July).
The Armenian calendar is divided into 12 months of 30 days each, plus an additional (epagomenal) five days are called aveleacʿ ("superfluous"). Years are usually given in Armenian numerals, i.e. letters of the Armenian alphabet, preceded by the abbreviation ԹՎ for t’vin "in the year" (e.g. ԹՎ ՌՆԾԵ "in the year 1455").
Jost Gippert, Old Armenian and Caucasian Calendar Systems in The Annual of The Society for The Study of Caucasia“, 1, 1989, 3-12.
Louis H. Gray, On Certain Persian and Armenian Month-Names as Influenced by the Avesta Calendar, Journal of the American Oriental Society (1907)
P'. Ingoroq'va, “Jvel-kartuli c'armartuli k'alendari” (“The Old Georgian pagan calendar”), in: Sakartvelos muzeumis moambe (“Messenger of the Museum of Georgia”), 6, 1929–30, pp. 373–446 and 7, 1931–32, pp. 260–336
K'. K'ek'elije, “Jveli kartuli c'elic'adi” (“The Old Georgian year”), in: St'alinis saxelobis Tbilisis Saxelmc'ipo Universit'et'is šromebi (“Working papers of the Tbilisi State University by the name of Stalin”) 18, 1941, reprinted in the author's “Et'iudebi jveli kartuli lit'erat'uris ist'oriidan” (“Studies in the history of Old Georgian literature”) 1, 1956, pp. 99–124.