Religious holidays calendar

How these dates are computed

Islamic dates use the project's Hijri engine, Jewish dates use the Hebrew calendar engine, Chinese New Year and Mid-Autumn use the Chinese lunisolar engine, and Nowruz uses the Persian calendar engine. Easter uses the standard Gregorian computus. Hindu dates use the local Vikram table where available and a hand table after that range. Vesak is hand-tabled because this codebase has no lunar phase module.

What one year of the table holds

Each year carries 18 dated observances drawn from seven traditions, which adds up to 180 entries across the decade. Multi-day festivals are shown as spans rather than single dates: Eid al-Fitr covers 3 days, Eid al-Adha 4 days, Rosh Hashanah 2 days, Passover 7 days, Hanukkah 8 days, Diwali 5 days, and Holi 2 days. Single-day entries such as Yom Kippur, Easter, Vesak, and Nowruz appear as one date.

Why the same holiday lands on different dates each year

Three different mechanisms drive the movement you see in the table. Purely lunar calendars, like the Islamic one, run about 11 days short of the Gregorian year, so Ramadan slides steadily earlier and works its way through every season. Lunisolar calendars, used for Jewish, Hindu, and Chinese dates, insert leap months to stay anchored to the seasons, so their festivals oscillate inside a window of a few weeks instead of drifting. Rule-based dates move within fixed bounds: Easter is the first Sunday after the paschal full moon and always falls between 22 March and 25 April, with Pentecost following exactly 49 days later. Nowruz tracks the March equinox through the Persian solar calendar, so it barely moves at all.

Computed dates versus observed dates

A computed calendar tells you when the astronomy or the arithmetic says a holiday falls. Observance can differ. Countries that begin Islamic months by sighting the crescent moon may start Ramadan or Eid a day earlier or later than the Umm al-Qura-aligned value shown here. Jewish holidays begin at sundown the previous evening, which matters for scheduling anything on the eve itself. Hindu dates can shift by a day between regional panchang traditions and diaspora calendars, and Vesak is fixed differently in Sri Lanka, Southeast Asia, and East Asia. For payroll cutoffs, product launches, or meetings with colleagues who observe these days, confirm against the official announcement for their specific country once it is published.

Common questions