Being Faatemi, Alavi Bohras use Hijri Lunar calendar which was established and published during the Fatimid rule in Egypt in the second half of 4th century AH/10th century AD. Before that the Imaam used to announce months and festivals verbally among his followers. The system of calculating months and days began right from the first prophet of Islaam, Aadam (as) and that knowledge continued from one prophet to another till the last prophet of Islaam, Mohammad ul-Mustafaa (saws) who came with the final message which also included how to calculate months and days.

This thing got transferred from tongue to chest into the holy Faatemi Imaams. Imaam is like a moon, so seeing the glowing (nooraani) face of Imaam and obeying his order for the commencement of a new month is like moon-sighting. The Misri-Alavi calendar has fixed number of days of each month based on the Lunar leap year (kabeesah) formula. An Alavi year has 355 days and in every 30 years 11 extra days are added i.e. in the span of 30 years; an extra day is added 11 times in different years in the last hijri month of Zul Hijjah making it 30 days, which has usually 29 days. All odd months have 30 days and all even months have 29 days. Therefore accordingly, the month of Ramazaan being an odd month always consists of 30 days. Da'iyullaah has strict control on printing of this calendar as the details of all important dates are noted in it with the timings of daily prayers. A single type of calendar is printed and is distributed in the whole community.