This article examines the sections on the daily calendar in Chapters One, Two, Fourteen, and Fifteen of Sharḥ-i Bīst Bāb by Mullā Muẓaffar Gunābādī. These chapters are devoted to the principles of calendrical reckoning, the structure and arrangement of the calendar, and the conversion and correspondence of chronological systems. The study discusses such topics as different types of solar and lunar years and months, various chronological systems, methods of date conversion, the use of abjad notation in recording calendrical data, the astronomical foundations of solar and lunar years and months, the structure of the Khaṭāʾī and Uyghur calendars, and the components and contents of the calendar, including its introductory page, the Ayyām-i Mashhūrah (well-known calendrical observances), and the recording of solar and lunar eclipses. In addition to explaining the theoretical foundations of calendrical reckoning, Mullā Muẓaffar provides a detailed account of the practical organization of the calendar and its constituent elements. Sharḥ-i Bīst Bāb may therefore be regarded as a valuable source for reconstructing the structure and contents of such calendars and for understanding calendrical practices in the Islamic tradition.