Why Ramadan and Eid dates differ from country to country

The first of the month is a decision, not a fact

A lunar month runs about 29.53 days, so a Hijri month has to be either 29 or 30 days long. Somebody has to decide which, twelve times a year, and the whole question of when Ramadan starts reduces to that one decision made at the end of Shaban.

The traditional basis for the decision is the sighting of the new crescent after sunset. The crescent is faint, low and visible for only a short window, so whether it can be seen on a given evening is genuinely marginal - and that is exactly why the answer can differ from one place to another on the same night.

A calculated calendar sidesteps the decision by fixing the month lengths in advance. That is useful for a printed calendar, a school timetable or an airline schedule. It is not the same thing as an announcement, and it was never meant to be.

The three things that vary

Almost every difference between two announcements comes down to one of three things, and none of them is a mistake.

Put those together and a one-day spread is not a sign that something has gone wrong. It is the expected outcome of a genuinely marginal observation being assessed by different people, in different places, under different criteria.

• Where you are standing. Crescent visibility depends on the Moon's altitude above the horizon at sunset and its separation from the Sun, both of which change with longitude and latitude. On a given evening the crescent can be comfortably visible in one part of the world and impossible in another.
• What counts as a sighting. Authorities apply different criteria - some require a naked-eye sighting, some accept optical aid, some accept testimony only from within a defined region, and some use astronomical calculation to confirm or exclude a claimed sighting.
• Whose announcement a community follows. Some communities follow their own local sighting, some follow the announcement of a particular country, and some follow a regional or national council. Two mosques in the same city can therefore begin on different days while both follow their stated method exactly.

What a calculated calendar can and cannot tell you

HijriConv computes dates from the Umm al-Qura calendar, the official civil calendar of Saudi Arabia, falling back to the arithmetic tabular calendar outside the years the official tables cover. Both are calculations. Neither observes anything.

What that gives you is genuinely useful: an exact, reproducible date you can put in a diary years ahead, a way to convert a Hijri date on a document into a Gregorian one, and a consistent frame for comparing years. The key-dates pages carry it for every year from 1970 to 2075.

What it does not give you is the day a fast begins or ends. That is determined by a religious authority, and the calculated date can land about a day either side of it. HijriConv states this on every page that shows a date, and it is not a formality - it is the actual limit of what arithmetic can do here.

This is also why you should not be surprised when a calculated date and a wall calendar disagree. The wall calendar may be following a different calculation, a different country's announcement, or a local council's decision from a previous year.

How large is the gap in practice?

Between two calculated calendars, the gap is small and bounded. Across the 132 month starts in the Hijri years 1440 to 1450, the Umm al-Qura table and the tabular civil calendar give the identical Gregorian day 82 times and differ by exactly one day the other 50 times. They never differ by two.

Between a calculation and a local announcement, expect the same order of difference: about a day, occasionally in either direction. Because Ramadan and the two Eids are each fixed to a particular day of a particular month, a one-day difference at the start of the month carries through to every date inside it.

For reference, here are the Umm al-Qura calculated dates for the most-searched observances in the next two years. Treat every row as a date that may move by a day.

Planning around a date that might move

The gap is a day. That is small enough to plan around, as long as you plan around it deliberately rather than discovering it the night before.

None of this requires knowing in advance which way the day will fall. It only requires treating the calculated date as an estimate with a known one-day tolerance, which is exactly what it is.

• Book flexibly around the edges. The first day of Ramadan and both Eids are the dates most likely to move; the middle of a month is stable.
• When you request leave, ask for the calculated day plus the day either side of it if you can, or say the date is subject to the moon sighting. Many employers and schools already understand the phrase.
• If you are organising something for a community, wait for the announcement your community follows before confirming, and tell people which announcement you are waiting on.
• If you are coordinating across countries, expect them to differ. Name the country's announcement you are using rather than just the date.
• Watch for the local announcement itself. That is the authoritative one for you, and no calendar - printed, app-based or this site - replaces it.

The one rule that always applies

Use the calculated dates for planning and never for the ruling. Every date on this site, including every row in the table above, is arithmetic: it comes from the Umm al-Qura tables or the tabular calendar, and it can differ by about a day from what is announced where you live.

For fasting, Eid, Hajj and every other observance, follow the announcement of your local religious authority. HijriConv exists to tell you what the calendars compute, which day of the week that lands on, and how the Hijri and Gregorian years line up - not to tell anyone when to begin.

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