It's the night before Ramadan. The family group chat has three different start dates, and your phone quietly disagrees with all of them. Every convert hits this moment and assumes they've misunderstood something. You haven't. Muslims share one lunar calendar; communities differ, for old and respectable reasons, on how a month is declared to begin. Here's how a date actually gets made, who the North American authorities are, and how to pick a lane and keep your peace.
Islamic months are lunar: 29 or 30 days, never more, never less. On the 29th evening, the question is whether the new crescent has been established, and that word "established" is where the methods split. The astronomical new moon (the conjunction) is a calculable instant, but a conjunction is not a visible crescent, and a crescent visible in Chile is not a crescent seen in Toronto. Between the astronomy and your mosque's announcement sit real decisions: whose sighting counts, from where, verified how, or whether a reliable calculation can stand in for sighting altogether.
Every camp agrees on the astronomy. What they weigh differently is the fiqh: local sighting honors the direct practice of looking; global sighting honors the unity of the ummah; calculation honors certainty and the ability to plan. Nobody in this list is being careless with the religion.
Five frameworks cover nearly every mosque in the US and Canada. Your mosque follows one of these whether or not it says so on the website.
Calculation. Ramadan and Shawwal are set in advance by astronomical criteria: at sunset, somewhere on the globe, the moon at least 8° from the sun and 5° above the horizon. Physical sighting is not required. Eid al-Adha follows the Hajj authorities' Arafah announcement. ISNA circulates FCNA's announcements.
Dates known months ahead; some communities reject calculation on principle.
Physical sighting first. The Hilal Committee of Metropolitan Toronto, for example, prioritizes local naked-eye sighting, uses astronomy only to reject impossible claims, and accepts verified reports from a defined zone of the Americas if Canada is clouded out. No sighting means the month completes 30 days.
Dates confirmed the night before; strong classical pedigree.
A verified sighting anywhere on Earth starts the month everywhere. The Hilal Council of Canada adopts this for all twelve months, filtering scientifically impossible reports, without automatically following any one country.
Often lands a day earlier than local-sighting mosques in the same city.
The month begins when Saudi Arabia announces it. Note the trap inside this: the Umm al-Qura calendar in your phone is Saudi Arabia's calculated civil calendar for planning. The actual religious dates come from separate sighting announcements and can differ from it by a day.
Simple to follow; ties your dates to another continent's announcement.
Jurist-based frameworks: the Crescent Committee of the Council of Shia Muslim Scholars of North America announces per Grand Ayatollah Sistani's sighting criteria, and followers of other maraji' follow their own authority.
A separate authority tree; don't assume the Sunni announcements cover it.
Your phone almost certainly displays the Umm al-Qura calendar, Saudi Arabia's pre-calculated civil calendar, or another calculated table. Your mosque may follow local moon sighting, global sighting, FCNA's calculation criteria, or Saudi announcements, and these can differ from the phone's table by a day in either direction. The phone isn't broken and neither is the mosque; they're answering different questions. For worship dates, follow your mosque's announcement, and treat the phone as an estimate.
Because the disagreement is about method, not astronomy. The moon's position is calculable to the second, what scholars genuinely differ on is what starts a month: a naked-eye sighting in your own region, a verified sighting anywhere on Earth, a calculation showing the crescent could be seen, or another country's official announcement. Each position has serious scholarship behind it, and respected North American institutions hold each one. That's why two mosques in the same city can both be right by their own method.
A new month can begin only after the astronomical new moon (conjunction), but conjunction isn't the trigger, visibility is. On the 29th evening of the month, observers look for the thin crescent just after sunset. If accepted testimony establishes a sighting, the new month starts that night; if not, the current month completes 30 days and the new month starts the following night. Committees verify testimony and use astronomy to filter out impossible claims.
The practical answer, echoed by scholars across positions: follow the mosque where you actually pray, its Jummah, its taraweeh, its Eid, and stay consistent rather than shopping dates year by year. If your household spans mosques with different methods, decide together in advance whose announcement governs your fasting and your Eid, and take genuine conflicts to a scholar you trust. Consistency is worth more than winning the annual argument.
Islamic dates begin at Maghrib, not midnight. So "the night of the 15th" comes before the daytime of the 15th, the first taraweeh of Ramadan happens the evening before the first fast, and Eid begins at sunset even though the prayer is the next morning. If a mosque flyer says an event is "on the 27th night," it means the evening before the 27th day.
Twelve lunar months of 29 or 30 days add up to 354 or 355 days, so the Hijri year runs about 11 days shorter than the solar year, and every Islamic date drifts earlier through the seasons on a roughly 33-year cycle. That's why Ramadan falls in winter for a few years, then spring, then summer. Years count from the Prophet's ﷺ migration to Madinah in 622 CE.
Request the two possible days early, "Eid will fall on one of these two dates; I'll confirm as soon as my community announces, likely the night before", and offer the swap or make-up arrangement that fits your workplace. US employees can request religious accommodation under Title VII, and Canadian protections run through federal or provincial human-rights law. It's general information, not legal advice, but the two-date request is standard practice and most employers handle it fine once it's explained.
The institutional methods above are described from each organization's own published criteria as of August 2026, and organizations occasionally revise their methodology. Future dates are always estimates until your community confirms them. Plan with two-day windows, and treat any printed "Eid date" as provisional until announced.