Why Do Muslims Start Ramadan on Different Days? The Science and Fiqh Behind the Split

Every year, without fail, the same question arrives in Muslim households, WhatsApp groups, and community centres around the world: why does our mosque start Ramadan on Wednesday when our cousins in another city begin on Thursday? The confusion is entirely understandable. A single month, a single moon, and yet multiple start dates. This is not a modern dysfunction. It is the product of genuine scientific complexity meeting a centuries-old jurisprudential debate, and neither side of the argument is as simple as it first appears. The whole question rests on how the Islamic lunar calendar works: a month that begins only when the new crescent is sighted.

The short answer is that Muslims start Ramadan on different days because of four overlapping factors. First, the crescent moon is genuinely visible in some parts of the world and not others on the same evening -- this is basic astronomy, not disagreement. Second, Muslim communities hold different positions on whether one confirmed sighting anywhere in the world is binding on all Muslims, or whether each region must sight the crescent for itself -- this is the question of matla. Third, communities disagree on whether astronomical calculation can substitute for physical sighting. Fourth, different nations follow different religious authorities, each issuing its own declaration.

Before going further, one clarification matters enormously. The "new moon" in the astronomical sense -- the moment of conjunction, when the Moon sits directly between the Earth and Sun -- is completely invisible. The hilal is something different: the first visible crescent that appears 15 to 40-plus hours after conjunction, once the Moon has gained enough separation from the Sun to be seen at twilight. For a full explanation of the distinction, see what is hilal.

Reason One: The Crescent Really Is Visible in Some Places and Not Others

The most important thing to understand about the crescent is that "tonight" is not a single global event. Sunset sweeps westward across the globe over 24 hours, and in the hours between Jakarta's sunset and Casablanca's, the Moon continues its orbital motion, gaining roughly 0.5 degrees of elongation from the Sun every hour. A crescent that is genuinely too thin to see at sunset in Indonesia may be comfortably visible by the time the Sun sets over Morocco several hours later. This is not a rounding error or a matter of opinion -- it is geometry.

Latitude adds a further layer of complexity. The angle at which the ecliptic -- the path the Moon follows across the sky -- meets the western horizon at sunset varies significantly with latitude. Near the equator, the ecliptic is steep, which means the Moon climbs quickly away from the Sun's glare in the minutes after sunset, making the crescent easier to see. At higher latitudes in northern Europe or Canada, the ecliptic meets the horizon at a shallow angle, and the Moon skims along near the horizon, often disappearing into haze before it can be properly seen. Two cities at the same longitude but different latitudes can receive opposite results on the same evening.

This is precisely why systematic visibility criteria are essential. The Yallop q-value, developed by Bernard Yallop at HM Nautical Almanac Office in 1997, computes a composite score from the arc of vision (ARCV, the vertical separation between Moon and Sun at sunset), the crescent width W, and the elongation (ARCL). The result places each location into one of six mutually exclusive bands: Zone A (easily visible to the naked eye) through Zone F (below the Danjon limit, so no crescent at all). Mohammad Odeh's (2004) V-value similarly divides the world into four visibility regions. The critical point is that moon age alone -- a figure often cited on social media -- is a very weak predictor. What matters is ARCV, ARCL, W, and lag time. Even with identical religious rules, a global visibility map on any given evening shows a curved frontier separating "visible" from "not visible." Start dates will naturally differ across that line.

Reason Two: One Sighting for the World, or One Sighting per Region? The Matla Question

Even when two communities agree on the astronomy, they may still disagree on what to do with the information. This is the question of matla (plural: matali), meaning roughly "the horizon" or the zone over which a given sighting is considered legally valid.

The two positions are:

Neither of these is a fringe or heretical view. Both are well-documented positions held by major classical scholars. The Hanafi and Hanbali tendency toward ittihad al-matali rests on the view that the Prophet's instruction to "fast when you see it" was addressed to the entire community, not just to those within visual range. The Shafi'i preference for ikhtilaf al-matali draws on the observation that the Companions in different cities did not automatically synchronise their months, and that the very concept of sighting implies a local horizon.

In practice, ittihad al-matali means that a sighting confirmed in, say, South Africa can start Ramadan for a community in Britain. Ikhtilaf al-matali means that the British community must establish the crescent over its own region. The same physical crescent, the same jurisprudential sincerity, and two different outcomes. For a detailed treatment of the debate, see global vs local moon sighting matla.

Reason Three: Sight the Moon, or Calculate It?

The third axis of disagreement concerns whether the physical act of sighting is obligatory or whether astronomical calculation can replace it.

The classical default, rooted in the Prophetic hadith "fast when you see it and break fast when you see it," is ru'ya: physical sighting. The instruction is explicit, and for most of Islamic history, calculation was either unavailable or trusted only as a tool to help observers know where and when to look, not as a substitute for observation itself.

The case for hisab (calculation) has grown stronger as computational astronomy has become extremely precise. Bodies such as the European Council for Fatwa and Research and the Fiqh Council of North America have accepted predicted visibility as a valid basis for declaring months. Crucially, most of these bodies do not calculate the conjunction and declare the month from there -- they calculate predicted crescent visibility. This keeps them closer in spirit to the sighting tradition: the question being asked is still "will the crescent be visible somewhere tonight?" Calculation and physical sighting therefore often agree.

The genuine grey zone arises in what the Yallop framework calls Zones C and D, and near the Danjon limit. The Danjon limit -- the minimum elongation below which the crescent cannot register on the human retina -- is commonly quoted at around 7 degrees, though debate continues over a range of approximately 5 to 7.5 degrees. In these marginal conditions, a CCD camera may capture an image that no human eye could detect. Does a CCD image constitute a sighting? Is a calculated prediction of marginal visibility sufficient to start the month? These questions have no universal answer in the classical sources, and reasonable scholars reach different conclusions. For the full scientific treatment of both approaches, see moon sighting vs calculation.

Reason Four: Different Countries Follow Different Authorities

The fourth factor is the most practically significant for most Muslims: the simple fact that different countries follow different institutions, each of which may apply one of the above positions in its own way.

The Saudi Declaration and the Umm al-Qura Calendar

A critical distinction is often lost in popular coverage. Saudi Arabia's civil Umm al-Qura calendar is a calculated administrative calendar used for civil purposes: holidays, government scheduling, and so on. The start of Ramadan and Eid is not taken from this calendar. It is declared separately by the Saudi Supreme Court, based on sworn testimony from sighting witnesses.

However, the Umm al-Qura calendar does follow a specific calculated rule introduced in 1423 AH: on the 29th of the current month, the month rolls over to the first of the new month if two conditions are met simultaneously -- geocentric conjunction must have occurred before sunset at Mecca, and the Moon must set after the Sun at Mecca that evening. According to analyses by astronomer Robert van Gent at Utrecht University, the crescent is still invisible to the naked eye from Mecca on roughly 75 per cent of the evenings that meet these two criteria. The Moon has only just cleared the Sun; it has not yet become a visible crescent.

The practical consequence was illustrated clearly in February 2026. On Tuesday 17 February 2026, the New Crescent Society stated that the crescent was astronomically impossible to see anywhere in Asia, Africa, or Europe that evening. Saudi Arabia nonetheless announced a sighting that evening and began Ramadan on Wednesday 18 February. The European Council for Fatwa and Research and a number of other bodies, relying on predicted visibility calculations and finding the crescent not yet visible, began Ramadan on Thursday 19 February. Both communities acted in good faith: the Saudi Supreme Court received sworn testimony from witnesses it found credible; the European Council applied its own validated methodology. The disagreement was not about values but about methodology and authority.

The Global Patchwork

Putting It Together: How One Lunation Becomes Three Different Start Dates

Consider a realistic lunation. Conjunction occurs on Monday evening. By Tuesday sunset, the crescent is barely visible from the western tip of North Africa and Central America -- Yallop Zone B or C. By Wednesday sunset, it is easily visible across most of the Muslim world.

A community following Saudi Arabia's sighting declaration, which received witness testimony on Tuesday evening, begins Ramadan on Wednesday. A community following the European Council for Fatwa and Research, which calculated that Tuesday's crescent was below the visibility threshold for Europe, begins on Thursday. A community in northern Britain committed to strict local sighting does not see the crescent on Tuesday or Wednesday due to cloud cover and waits until Thursday's clear sky confirms it, beginning on Friday. All three outcomes are internally consistent. None involves deliberate error.

The same logic that produces three Ramadan start dates also governs Eid al-Fitr at the end of the month and Eid al-Adha ten days into Dhul Hijja. For upcoming dates, see Eid 2027 date.

Frequently Asked Questions

Why does Saudi Arabia sometimes start Ramadan before everyone else?

Saudi Arabia's Ramadan declaration follows a sighting process closely tied to the Umm al-Qura calendar, whose threshold requires only that the Moon sets after the Sun at Mecca on the evening of the 29th. Because that threshold is met before the crescent becomes optically visible to the naked eye, witness testimony sometimes arrives earlier than visibility maps would predict. Astronomers note that on roughly three quarters of qualifying evenings the crescent is below naked-eye detectability, which explains why other countries using optical visibility criteria begin a day later.

Is it wrong to start on a different day from another country?

No. Both ittihad al-matali (one sighting for all) and ikhtilaf al-matali (each region sights for itself) are established classical positions documented across the major schools of jurisprudence. Following your recognised local religious authority, whichever methodology it applies, is valid. The disagreement is about methodology, not piety.

Does the Moon's age decide visibility?

No. Moon age, measured in hours from conjunction, is a commonly cited but weak predictor of visibility. The real drivers are ARCV (arc of vision, the vertical separation between Moon and Sun at sunset), ARCL (elongation, the angular distance between Moon and Sun), crescent width W, and lag time (how many minutes after sunset the Moon sets). Two locations with identical moon ages can have opposite visibility outcomes due to differences in latitude and the ecliptic angle.

How can I check whether the crescent is visible where I live?

Use a visibility map that computes the Yallop q-value and Odeh V-value for your exact geographical coordinates and the local sunset time. Global averages and moon age figures are insufficient. A proper tool will show you which Yallop zone you fall into and whether you are above or below the optical-aid threshold.

Conclusion: A Difference Rooted in Geometry and Good-Faith Jurisprudence

Muslims start Ramadan on different days because of four overlapping realities: the crescent is genuinely visible in some locations and not others on the same evening; communities hold different scholarly positions on whether a distant sighting is binding; communities disagree on whether calculation can substitute for physical observation; and different nations follow different religious authorities applying these positions in different ways.

None of these disagreements is new, and none is evidence of confusion or failure. The Islamic lunar calendar is a decentralised, living tradition that has always grappled with a genuinely difficult astronomical problem: the first crescent is the thinnest, most fleeting object in the sky, visible for a narrow window at the worst possible time -- low on the horizon, in the glow of a setting sun. That serious scholars across fourteen centuries have reached different conclusions about how to handle that difficulty is not a scandal. It is evidence that the tradition takes the problem seriously.

Clear skies and happy sighting.

See Also

• Does the Umm al-Qura Calendar Follow the Crescent? 300 Months Checked Against the Sky
• What Is Moon Sighting? The Complete Guide to the Crescent, the Hijri Calendar, and the Science of Visibility
• Ramadan dates 2027 to 2035

References

• Yallop, B. D. (1997). A Method for Predicting the First Sighting of the New Crescent Moon. NAO Technical Note No. 69, HM Nautical Almanac Office.
• Odeh, M. S. (2004). New Criterion for Lunar Crescent Visibility. Experimental Astronomy, 18, 39 to 64.
• Danjon, A. (1936). Le croissant lunaire. L'Astronomie, 50.
• van Gent, R. H. The Umm al-Qura Calendar of Saudi Arabia. Utrecht University. https://webspace.science.uu.nl/~gent0113/islam/ummalqura_rules.htm
• Middle East Eye. Saudi announces Ramadan Wednesday, most others start day later. https://www.middleeasteye.net/news/saudi-announces-ramadan-wednesday-most-others-start-day-later
• European Council for Fatwa and Research. General Secretariat statement on Ramadan and Shawwal 1447 AH. https://www.eumuslims.org/en/statement-by-the-general-secretariat-of-the-european-council-for-fatwa-and-research-on-determining-the-beginning-of-ramadan-and-shawwal-for-the-year-1447-ah-2026/
• Al Jazeera. When is Ramadan 2026 and how is the moon sighted. https://www.aljazeera.com/news/2026/2/16/when-is-ramadan-2026-and-how-is-the-moon-sighted