Saadoe'ddin Djambek was an astrological reformer in West Sumatra who wrote many scientific books. Almanac Djamiliyah, one of his works, serves as a reference for determining the beginning of the month and prayer times. The calendar concept used in Almanak Djamiliyah comes from a combination of astronomical theories and scholarly thinking. In addition, Saadoe'ddin Djambek's thought patterns underwent stages of progress so that he could produce an Islamic interpretation that could solve the problems of hisab thinking and the problems faced by his people. Although the Djamiliyah Almanac was intended for West Sumatra, there are some corrections that make the prayer time schedule usable for all countries up to 10° north and south of the equator. In this paper, the author divides it into two problem formulations: how the Djamiliyah Almanac was made by Saadoe'ddin Djambek and how the concept of calendar and prayer times was used in it. It is hoped that this work will add to the collection of falak science and serve as a source of information and reference for future researchers.