This thesis focuses on comparative Study on the computus of Abušakǝr and Demetrius. From 1993 to1995 EC, as the researcher was a student of Abušakǝr in Däbrä Libanos Monastery, he had many questions on the computus of Abušakǝr and Demetrius. This problem motivated to study on this topic. The specific objectives of the study are investigating the logical difference between Abušakǝr and Demetrius and solving hidden issues of Abäqte and Mäṭqǝʿ. This thesis reviewed Qämärä Näbiyat, Qämärä Gwǝndagwǝndi, Qämärä Bizän and Qämär Arab. He gathered primary data from IES, the Library of The Holy Trinity Theological University, The Library of See of Patriarchate and Ethiopian National Library Agency and supplementary data from the interview of scholars of EOTC. Document analysis and interview are selected as data gathering tools for this study. The data analyzed in qualitative research methodology. The study showed in detail that there is logical difference between the two scholars, and solved the hidden issues of Abäqte and Mäṭqǝʿ. He concluded that the two scholars of calendar have their own logical difference. Abušakǝr followed laws of theorem while Demetrius followed postulate. Another important findings are, Abäqte = 11*Wänbär (W), (Where value of Wänbär is a whole number, which is 0 ≤ W ≤2), Abäqte = Wänbär) – (30*n). Where the value of Wänbär is 3 ≤ W ≤18 and n is a whole number which is 1≤ n ≤ 6 and that the fraction number of 1śalsit will be full hour (24 hour) after the end of 600 years without any last bit fraction. He also recommended for newcomer researchers who want to study around the calendar if they will focus on the following topics: Ḥässabä Mänazl, Tǝrrafatä ʿAwdä, ʾAʾǝgarä Ṣäḥay, Śärqä wärḫ and Täwsakä wärḫ. Because the topics are new and have, good secrete behind them.