Calendar
These dates are estimates, not fixed calculations — the actual date depends on a physical moon sighting confirmed only days beforehand.
The Islamic (Hijri) calendar is purely lunar, and traditionally each new month begins only once the crescent moon is actually sighted after sunset — not from a fixed astronomical calculation. That means the start of Ramadan, and therefore Eid al-Fitr at its end, along with Eid al-Adha months later, can only be predicted approximately in advance; the confirmed date is typically announced just a day or two ahead by religious authorities once the moon is actually observed (or, in some countries, based on astronomical calculation rather than sighting, which can itself lead to different countries observing the same holiday a day apart).
The dates in the table are astronomical estimates — when the relevant new moon is expected to be visible — which is why later years are increasingly marked "estimated" rather than confirmed. Treat anything more than a year or so out as a planning approximation, and check a local or national Islamic authority's announcement closer to the date for the confirmed day.
Related
Check the new moon phase behind any estimated date directly.
A different lunar calendar, with its own reliable calculation method.
A lunar-based holiday that IS fixed by calculation, not sighting.