The Single Global Hijri Calendar (SG Hijri Calendar) Fosters Unity among Muslims
By: Ali Aminulloh
Every year, the arrival of Ramadan is marked by a recurring theme: differences in dates among Muslim communities. Some begin fasting based on rukyat (the sighting of the crescent moon), others follow hisab (astronomical calculations), and still others make local compromises stemming from their respective traditions and religious authorities. This year, the debate has taken a new turn: the official initiative to unify the global Hijri calendar, the Single Global Hijri Calendar (SG Hijri Calendar). This idea is not simply about numbers; it challenges the way Muslims understand religious time, the authority of its determination, and the relationship between tradition and science. The Muhammadiyah Association plays a central role in this process, not only as the initiator but also as the initial implementer.
Background: Why is a single calendar needed?
The classic problem is simple: differences in methods lead to inconsistent observances of the main religious days: Ramadan, Eid al-Fitr, and Eid al-Adha. The practical impacts include social confusion, disruptions to economic and educational rhythms, and even a symbolic rupture in the discourse of “one ummah.” Throughout modern history, a number of Muslim scholars and researchers have proposed calendars that rely on astronomical calculations to guarantee date certainty, but these ideas have often been hampered by theological objections, methodological differences (e.g., crescent visibility criteria), and geopolitical factors. These study documents cite the long history of this idea and attempt to assess solutions that meet both the demands of sharia and practical global needs.
Who pioneered the KHGT (Islamic Hijri Calendar) and what were their motives?
The modern initiative, known as the KHGT, was conceived, developed, and publicly launched by the Muhammadiyah Association through its bodies dealing with Islamic jurisprudence and hisab (Islamic jurisprudence), specifically the Tarjih and Tajdid Council. The official launch took place within a series of academic and dissemination activities publicized by the organization in mid-2025, with a clear goal: to provide a single, consistent, scientific, and globally applicable Hijri calendar. The motivation stated in the launch materials was to “repay the debt of civilization,” namely, to design a calendar system that combines astronomical precision and sharia-compliant compliance for the sake of one day, one date, for all people.
Goals and Promised Benefits
The KHGT is designed with four core goals: (1) uniformity of dates and days worldwide; (2) certainty of the calendar that can be planned in advance (administrative and social benefits); (3) a transparent scientific basis for accountable decisions; and (4) minimizing political or local ritual conflicts. Practical benefits include consistency of holidays, coordination of cross-border activities (e.g., educational planning, international congregational worship), and reducing the burden of annual debates that often consume the energy of the community. The official KHGT document and launch summary outline these benefits and highlight technical features such as crescent visibility maps and date conversion.
Determination Method: Contemporary True Calculation and Visibility Parameters
The KHGT does not opt for pure rukyat or a rigid tabular calendar: it uses contemporary true calculus, a modern astronomical calculation that takes into account the geocentric position of the Moon–Sun, the age of the moon, and the young crescent visibility parameter, then applies certain validity criteria to determine when a new month begins globally. In its technical documentation, the KHGT presents maps and tables showing areas that meet the parameters (e.g., astronomical conditions at the reference point chosen by the calendar maker). There is also a scientific communication procedure between hisab experts and Islamic jurisprudence institutions before the determination is announced.
One distinctive note: when the KHGT determines a day (e.g., 1 Ramadan 1447 AH falls on February 18, 2026), the technical explanation lists the underlying astronomical data, including observations and calculations at specific coordinates (in public communications, references are even made to locations such as Alaska as examples of global astronomical conditions). This demonstrates an effort to link the calculations to a retestable reference point.
Who is involved in the preparation and determination?
The development of the KHGT involved a cross-disciplinary team: astronomy/hisab experts, Islamic jurisprudence scholars (particularly the Tarjih and Tajdid Council), academics from relevant universities (e.g., Aisyiyah University in Yogyakarta, which hosted the launch), and a technical team that prepared the software and visibility maps. Muhammadiyah’s role as the fostering institution, integrating Islamic jurisprudence and science studies, was central to this initiative, while academics provided technical arguments and supporting publications. The KHGT document and pocketbook list the bodies and teams that formulated the KHGT parameters and methods.
The reality of implementation: who is already using it?
In the initial stages, the KHGT was institutionally adopted by the Muhammadiyah Association itself, meaning this calendar decision applies within the organization, educational institutions, and its charitable network. Global adoption is still a process: several local studies and surveys in Indonesia are assessing public readiness for this calendar, and academic publications have begun discussing its socio-legal implications. In other words, the KHGT has not automatically replaced the practice of determining it in other countries, but it has become a serious reference that has sparked discussions between schools of thought and religious bodies.
Critical Notes and Remaining Questions
Every normative innovation requires legitimacy, not just technical, but also theological and social. Several questions remain relevant: how widely accepted is it by the community, which has been accustomed for centuries to local rukyat (traditional rukyat) practices? How does the KHGT mediate claims of religious sovereignty between the state and local authorities? Do the chosen visibility criteria truly meet the requirements of sharia according to various schools of thought? Emerging academic studies indicate the need for public education and inter-institutional dialogue to prevent new friction.
Epilogue: More Than a Calendar
The KHGT is not just a table of dates; it is a claim about how modern people can harmonize ritual with science without losing the rationale of Islamic law. For some, this is a civilizational leap: providing certainty and minimizing conflict. For others, it forces us to reconsider the authority of tradition. Are people ready? The answer is not merely technical—it is cultural and spiritual. The healthiest discussion is certainly not one of dogmatic rejection or acceptance, but rather of scientifically testing the claims, examining their social consequences, and opening up a space for dialogue among global Islamic organizations to consider the future of a calendar that can unite more hearts than it divides.**
Indonesia, February 19, 2026
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