How Islamic Dates Are Determined: Sighting, Calculation and Authority
Practical confusion about Islamic dates is universal — apps, mosques and countries often differ on when Ramadan or Eid falls. This guide explains the machinery: the moon, the sighting committees, the calculations, and why a date announced one place may differ from another. Once you understand it, the 'confusion' becomes a system.
The command to sight the moon
The Prophet (peace be upon him) is recorded instructing: 'Fast when you see it [the crescent], and break your fast when you see it' (Sahih al-Bukhari; Sahih Muslim). This established sighting as the primary method of the Islamic calendar. The Qur'an reinforces the moon's role as a time measure for people and for Hajj (2:189).
How sighting works
A new month begins when the new crescent is visibly confirmed after sunset following the astronomical new moon. Sightings are typically organised by authority: members observe the western horizon after Maghrib, report sightings, and an announcement follows — sometimes aided by telescopes and astronomy.
How calculation works
Astronomy can predict exactly when the astronomical new moon occurs and whether a crescent is likely visible at a given location (using criteria such as the moon's age, altitude and elongation after sunset). Many Muslim-majority countries now begin months by calculation or by a hybrid: calculation-assisted, sighting-confirmed. Apps and this platform use the arithmetic/tabular calendar (or Umm al-Qura) for estimates.
Why announcements differ
Different authorities differ on three things: whether they sight or calculate, what visibility criteria they use, and whose sighting reports they accept. So the crescent visible in Makkah may not be accepted by a committee in another region, and a calculated date may differ from a sighted one by a day. Both systems are legitimate, and the scholars debate them respectfully.
Practical guidance
For Ramadan, Eid and Hajj, follow a recognised authority — your country's council, your masjid's affiliation, or a trustworthy international body — and plan your worship around its announcement. Treat app calendars (including this one) as estimates, and note the platform always labels its dates as calculated, not announced.
Frequently asked questions
Should I follow Makkah's announcement or my local one?
Scholars differ: some say beginning with the local region's sighting, others say the sighting of Makkah, still others a global sighting. The commonly recommended practice is to follow the recognised authority in the place you live. For personal guidance, ask a qualified scholar.
Can Eids fall on different days in different countries?
Yes — regularly. When the crescent is sighted in one country and not another, the countries begin the next month — and therefore Eid — on different days. It is expected, not an error.
Sources
- Quran 2:189
- Sahih al-Bukhari & Sahih Muslim (fast upon sighting)
- Sunan al-Nasa'i and others (the hadith of the unlettered: a month is 29 days or 30)
- Contemporary rulings of national and international fiqh councils
Last content review: 2026-09-25. How Destiny Map selects and verifies sources is explained on the Sources & Methodology page.
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