If you’ve ever compared the Hijri date shown in Saudi Arabia to the one your app or a website in another country is displaying, you may have noticed they don’t always match — sometimes by a full day. This isn’t an error on either side. It comes down to how each country determines when a new Islamic month begins.

It all comes down to moon sighting, not a shared calendar

Unlike the Gregorian calendar, which is fixed years in advance, the Hijri calendar in its traditional form depends on physically sighting the new crescent moon at the end of each month. Saudi Arabia’s Supreme Court manages this centrally through official observers. Other countries either run their own local sighting committees, rely on regional Islamic authorities, or in some cases apply pre-calculated astronomical tables instead of waiting for a physical sighting. Each of those approaches can arrive at a slightly different answer for the same evening.

Geography genuinely changes what’s visible

A new crescent moon isn’t equally visible everywhere on Earth on the same night. Its position, angle, and brightness relative to the horizon shift depending on longitude and latitude, and weather conditions like cloud cover, dust, or haze can hide a crescent that would otherwise be visible. So it’s entirely possible for observers in Saudi Arabia to confirm a sighting on a given evening while observers in, say, Southeast Asia or North America genuinely can’t see it yet from their location — leading those regions to start the new month a day later.

Some countries follow Saudi Arabia; others don’t

Several Gulf countries — the UAE, Qatar, Kuwait, Bahrain, and Oman — typically align with Saudi Arabia’s announcement, both for religious and practical regional-coordination reasons. Countries like Pakistan, India, Bangladesh, Morocco, and Indonesia generally run their own independent sighting committees and announce dates based on what’s observed locally, which is why headlines about Ramadan, Eid, or Muharram starting “a day apart” in different parts of the world show up almost every year.

Why calculated calendars and apps can disagree with all of the above

Many websites and apps display Hijri dates generated by an algorithm that predicts, months or years in advance, exactly when each lunar month “should” start based on astronomical conjunction. That’s useful for planning, but it’s a projection, not an official ruling — and it can end up a day off from whichever country’s actual sighting-based announcement you’re comparing it to. If you need the authoritative date for religious observance in Saudi Arabia specifically, the Supreme Court’s official announcement is the one that counts, not a calculated app date.

Frequently asked questions

Is one country’s Hijri date “correct” and another “wrong”?

Not really — both can be legitimate outcomes of following their own moon-sighting or calculation methodology. The difference reflects methodology, not error.

Which date should I follow?

Generally, the one officially announced by the Islamic authority in the country where you’re located, unless your local mosque or community follows a specific alternative practice.

Why does Saudi Arabia sometimes start a month a day before everyone else?

Because it relies on its own local sighting reports, which can confirm a crescent that isn’t yet visible from other regions due to geography or weather.