Ramadan 2026: Predicting the Start Date with Science & Hilal Criteria

Jakarta – The anticipated start of Ramadan 1447 AH, or 2026 CE, is generating discussion among Muslims in Indonesia, with potential differences arising from varying criteria used in its determination. The calculation isn’t solely based on naked-eye observation, but relies on precise astronomical calculations.

According to research from the National Research and Innovation Agency (BRIN) and the Indonesian Agency for Meteorology, Climatology, and Geophysics (BMKG), differing interpretations of lunar visibility criteria are expected to lead to slightly different start dates.

Local vs. Global Hilal Criteria

Thomas Djamaluddin, Coordinator of Astronomy at BRIN’s Center for Space Research, explained that the potential discrepancy this year isn’t due to the moon’s position being difficult to observe, but rather to differing interpretations of “local” and “global” hilal (crescent moon) criteria.

“There will be a difference in the determination of the beginning of Ramadan 1447. The source of the difference isn’t like before, related to the moon’s position, but is caused by the difference between ‘local hilal’ and ‘global hilal’,” Djamaluddin said, as reported by detikNews.

Local Hilal Criteria (MABIMS)

This criteria, used by the Indonesian government (Ministry of Religious Affairs) and the majority of Islamic organizations, requires the hilal to be visible in Indonesian territory with a minimum altitude of 3 degrees and an elongation of 6.4 degrees.

Global Hilal Criteria

This criteria is used by Muhammadiyah, one of Indonesia’s largest Islamic organizations. The principle is that if the hilal meets visibility criteria anywhere on Earth, and the conjunction occurs before dawn in New Zealand, the new month has begun.

Astronomical Analysis

Based on BMKG data, the geosentric conjunction – when the Moon and Sun are in the same ecliptic longitude – is predicted to occur on Tuesday, February 17, 2026, at 7:01 PM local time (WIB).

Scientifically, What we have is a crucial point. Because the conjunction occurs after sunset in Indonesia, on the evening of that day:

• The position of the hilal is still below the horizon (negative).
• The hilal’s altitude ranges from -2.41° in Jayapura to -0.93° in West Sumatra.
• The moon’s age is negative, meaning the hilal hasn’t “born” yet at sunset.

for those using the Local Hilal criteria, the month of Sha’ban will be completed (istikmal) to 30 days, and the first day of Ramadan 1447 AH is predicted to fall on February 19, 2026.

Conversely, those using the Global Hilal criteria look beyond national borders. Djamaluddin noted that on February 17th, the moon’s position already meets visibility criteria in Alaska, United States.

Because the conjunction occurred before dawn in New Zealand and the hilal already “exists” globally, this group is likely to determine the first day of Ramadan 1447 AH as February 18, 2026.

For those awaiting the Indonesian government’s isbat (confirmation) hearing, observation (rukyatul hilal) will only be effective on the evening of February 18, 2026. At that time, scientific data indicates the hilal’s position will be significantly more favorable:

• Hilal Altitude: Reaching 7.62° in Merauke to 10.03° in Sabang (well above the 3° requirement).
• Elongation: Between 10.7° and 12.21° (exceeding the 6.4° requirement).
• Moon’s Age: Reaching 20 to 23 hours.

With such a high position, the hilal is expected to be easily visible through telescopes or even the naked eye, provided the weather is clear.

Despite the clarity provided by scientific calculations (hisab), the Indonesian government will still hold an isbat hearing on February 17, 2026. This hearing serves as a formal confirmation between mathematical calculations and field facts through hilal observation.

Science doesn’t aim to create conflict, but to provide objective data so that people can understand why differences occur. As Prof. Thomas Djamaluddin stated, there is no flawed data astronomically; differences arise only because of differing criteria.