Which lunar calendar is used to determine Ramadan's dates?

The Islamic calendar is the lunar calendar used to determine Ramadan’s dates.

Its months follow the Moon rather than the solar year. Ramadan begins with the ninth month, traditionally confirmed when the first visible crescent appears after the new moon. Because lunar months last about 29 or 30 days, the calendar year is shorter than the Gregorian year.

This means Ramadan moves through the seasons over time. It may begin in summer one decade and winter several years later, rather than staying in the same Gregorian month. Communities can also differ by a day because some rely on local crescent sightings while others use astronomical calculations or an official calendar.

The Islamic calendar is also called the Hijri calendar because its era begins with the Hijra, Muhammad’s migration from Mecca to Medina in 622 CE. The Gregorian calendar is solar, the Hebrew calendar is lunisolar, and the Coptic calendar is primarily solar, so none is the calendar that directly sets Ramadan’s month.