Ramadan Date Calculator

Ramadan is the ninth month of the Hijri calendar, a strictly lunar reckoning in which each month begins with the first visibility of the new crescent, or hilal. Twelve synodic months of 29.530589 days each total about 354.37 days, which is 10.88 days short of the 365.2422-day tropical year. That deficit governs this calculation: Ramadan retreats through the Gregorian calendar by roughly eleven days annually and completes a full circuit of the seasons in about 33 years, so a Muslim living a normal lifespan fasts in every season. Each Ramadan runs 29 or 30 days, and the following day, 1 Shawwal, is Eid al-Fitr. Eid al-Adha falls on 10 Dhul-Hijjah, about 70 days later. Because visibility of a thin crescent depends on elongation from the sun, altitude at sunset and atmospheric conditions, predicted and observed start dates diverge. Crescents below roughly 7 degrees of elongation, the Danjon limit, cannot be seen at all, and practical naked-eye thresholds are higher. Saudi Arabia's Umm al-Qura calendar uses a calculated criterion based on geocentric conjunction before sunset and moonset after sunset at Mecca, while many other authorities require a reported physical sighting, so neighbouring countries commonly begin Ramadan one or two days apart. Tabulated dates such as these should be treated as estimates within plus or minus one to two days of a local declaration. Fasting runs from Fajr, true dawn when the sun is about 18 degrees below the horizon, to sunset at Maghrib, giving durations from roughly 13 hours near the equator to over 20 hours at high northern latitudes in summer.

The Hijri era was established under the second caliph Umar ibn al-Khattab around 638 CE, some sixteen years after the event it commemorates, with 1 Muharram of year 1 AH corresponding to 16 July 622 CE in the Julian calendar. Pre-Islamic Arabia had used a lunisolar scheme with an intercalary month, nasi, inserted to keep lunar months aligned with the seasons and the pilgrimage. That practice was abolished by the Quranic injunction in Surah at-Tawbah, which fixed the year at twelve months, and the calendar has been purely lunar ever since, with no mechanism for seasonal correction. Medieval Islamic astronomers developed the tabular Hijri calendar, a 30-year arithmetic cycle containing 11 leap years of 355 days, which underlies most modern conversion software and was already in use in the work of al-Khwarizmi in the ninth century and al-Battani shortly after. The tension between calculation and observation has never fully resolved. Saudi Arabia introduced the Umm al-Qura calendar for administrative purposes in 1346 AH, corresponding to 1927 CE, and revised its visibility criteria several times, most substantially for 1420 AH in 1999. Coordination efforts in the modern era include the Islamic Crescent Observation Project, founded in 1998 by the Jordanian astronomer Mohammad Odeh, which collects and publishes worldwide sighting reports, and the decision of the Fiqh Council of North America in 2006 to adopt astronomical calculation rather than local sighting for determining the start of Ramadan in North America.