Unlocking the mathematical algorithms behind the Ethiopian orthodox tewahedo church calendar

This study bridges a critical gap by formalizing the mathematical algorithms of the Ethiopian Orthodox Tewahedo Church’s (EOTC) calendar, the Bahre Hasab. Despite its significance, these computations remain largely inaccessible, preserved in Ge’ez manuscripts and orally by ecclesiastical scholars (Alemiyan). Employing a qualitative approach with expert interviews in Tigray, this research systematically extracts and documents the core procedures. It elucidates the theological chronology of Amete Alem and deconstructs the hierarchical cyclical system of Abiy Qemer (532-year cycle) and Nius Qemer (19-year cycle) that manages solar-lunar discrepancies. The study formalizes algorithms for calculating key variables like Abeqte and Metqie and demonstrates their application through an algebraic system of Tewsak values to determine movable feasts. This work translates ancient knowledge into a standardized, reproducible format, preserving intangible cultural heritage and providing a vital resource for scholars and the global community.