Which Caliph first introduced the Hijri Calendar?

The Hijri Calendar, also known as the Islamic lunar calendar, was first introduced by Hazrat Umar ibn al-Khattab (RA), the second Caliph of Islam. Its introduction marked a significant development in the administrative and religious life of the early Muslim community. The calendar begins from the year of the Hijrah, the migration of Prophet Muhammad (PBUH) and his companions from Makkah to Madinah in 622 CE. This event was chosen as the starting point because it represents a turning point in Islamic history, transitioning the Muslim community from persecution to establishing an organized society under Islamic guidance.

Hazrat Umar (RA) initiated the calendar during his caliphate to standardize the recording of events, financial transactions, and important religious dates such as Hajj and Ramadan. Before the introduction of the Hijri Calendar, Arabs relied on a loosely organized system of lunar months and seasonal markers, which caused confusion in trade, taxation, and religious observances. By establishing a unified system, Hazrat Umar (RA) ensured that the community had a consistent and accurate way to track time in accordance with Islamic principles.

The Hijri Calendar is based on 12 lunar months, totaling approximately 354 or 355 days, making it shorter than the solar calendar. This lunar system gives Islamic months their unique characteristics, causing festivals and rituals like Ramadan and Eid to shift approximately 10–11 days earlier each solar year.