How We Calculate Dates

Last updated: 8 November 2026

Every date on EasyDateCalc comes from one of three places: a published algorithm, a calendar conversion, or an official announcement. Here is which one we use for what.

Islamic dates (Ramadan, Eid)

We convert dates with the Umm al-Qura calendar used in Saudi Arabia. Islamic months officially begin with the sighting of the new crescent, so these dates are labelled "expected" and may shift by one day, and different countries can differ. Where a government has already gazetted a date (for example Singapore's Ministry of Manpower), we show that date for that country.

Hindu dates (Holi, Diwali)

Holi and Diwali follow the lunisolar Hindu calendar, and the exact day can vary by region because a lunar day does not begin at midnight. We use the dates on India's central government holiday list where available and cross-check published panchang calendars. Years we could not confirm are marked as expected.

Chinese and Vietnamese lunar dates

Chinese New Year, Tet and the Mid-Autumn Festival are converted from the Chinese lunar calendar and cross-checked with the Hong Kong Observatory's conversion tables.

Hebrew dates

Hanukkah begins on 25 Kislev; we convert with the standard arithmetic Hebrew calendar. The first candle is lit the evening before the first day.

Easter

Western Easter uses the Gregorian computus (the anonymous "Meeus/Jones/Butcher" algorithm); Orthodox Easter uses the Julian computus converted to the Gregorian calendar.

Public holidays

UK bank holidays come directly from GOV.UK's official data. US federal holidays follow the Office of Personnel Management rules, including observed dates. Singapore holidays come from the Ministry of Manpower's gazetted list. Other countries come from the open Nager.Date dataset and are labelled as such.

Week numbers and full moons

Week numbers follow ISO 8601. Full moon times are computed with Jean Meeus's lunar phase algorithm (accurate to a few minutes) and given in UTC.

Countdowns

Countdowns run in your browser and use your device's clock and time zone, counting to local midnight on the target date.

Corrections

If you find a mistake, please contact us. We review and update pages regularly; each page shows its last update date.

Sources: GOV.UK – UK bank holidays · OPM – Federal holidays · MOM Singapore – Public holidays · Hong Kong Observatory – Calendar conversion · Nager.Date