Yogyakarta. Indonesia’s second-largest Islamic organization, Muhammadiyah, will officially launch a Global Unified Hijri Calendar (KHGT) on Wednesday at Aisyiyah University (UNISA) in Yogyakarta.

The KHGT aims to provide a standardized, scientific lunar calendar for Muslims worldwide, helping eliminate long-standing discrepancies in determining major Islamic holidays such as Ramadan, Eid al-Fitr, and Eid al-Adha. The Hijri calendar, based on lunar cycles, consists of 12 months and is used by Muslims to schedule religious observances. Variations in moon-sighting methods often lead to different countries celebrating these holidays on different days.

“Islam is a global phenomenon. Its followers are spread across the world,” said Muhammad Rofiq Muzakkir, secretary of Muhammadiyah’s Tarjih and Tajdid Council. “As a universal religion, Islam needs a universal timekeeping system that can synchronize religious practices and daily life.”

The calendar is designed to strengthen unity among Muslims and modernize Islamic traditions while promoting social and religious integration across cultures. The launch event will be attended by high-ranking officials, including Muhammadiyah Chairman Haedar Nashir, Indonesia’s deputy foreign minister, foreign ambassadors, a representative from Turkey’s Directorate of Religious Affairs (Diyanet), and the secretary-general of the Organization of Islamic Cooperation (OIC).

In addition to the official launch, organizers will host an international seminar to discuss the calendar’s methodology, scientific basis, and implementation. Muhammadiyah hopes the discussion will foster open academic and cross-cultural dialogue on standardizing the Islamic calendar.

Officials acknowledge that local customs and traditions may present challenges to widespread acceptance of the KHGT. The organization plans to focus on education and dialogue in encouraging broader adoption.

Muhammadiyah said the KHGT is not only a step toward global synchronization of Islamic worship but also a symbol of Muslim solidarity and a contribution to a more advanced and united Islamic civilization.