How the lunar calendar works

Each Islamic month follows the moon and lasts 29 or 30 days. A year of twelve months is therefore 354 or 355 days long. The Quran mentions twelve months in the year in the sight of Allah (Quran 9:36), and it says the moon is a way to know time (Quran 10:5).

A new month begins when the new crescent moon is seen, or in some places by calculation. A day in this calendar begins at sunset, not at midnight.

Many Muslims keep both calendars. They use the Gregorian calendar for daily life and the Hijri calendar for worship and for remembering Islamic events.

Where the year count comes from

The years are counted from the Hijrah, the migration of the Prophet ﷺ and his companions from Makkah to Madinah. The year count was set in the time of the caliph Umar (may Allah be pleased with him). The first month of the year, Muharram, was chosen as the start. The abbreviation AH means "after Hijrah".

The migration itself took place in the year 622 of the Gregorian calendar, and it is remembered as a turning point for the Muslim community.

The twelve months in order

Here are the months in their order, with a short note on some of them.

  • Muharram: the first month, and one of the sacred months. The day of Ashura falls on the 10th.
  • Safar
  • Rabi al-Awwal
  • Rabi al-Thani (also called Rabi al-Akhir)
  • Jumada al-Ula
  • Jumada al-Thani (also called Jumada al-Akhirah)
  • Rajab: one of the four sacred months.
  • Shaban: the month before Ramadan.
  • Ramadan: the month of fasting, in which the Quran was first revealed.
  • Shawwal: Eid al-Fitr is on its first day.
  • Dhul Qadah: one of the sacred months.
  • Dhul Hijjah: the month of Hajj, and one of the sacred months. It includes the Day of Arafah and Eid al-Adha.

Why the dates move against the Gregorian calendar

The Gregorian calendar follows the sun and has 365 or 366 days. The Hijri year is about ten or eleven days shorter. Because of this, each Islamic date falls about ten or eleven days earlier in the Gregorian calendar every year.

This is why Ramadan moves through all the seasons. Over about 33 years, it falls once in every part of the Gregorian year. Muslims in every land share this change, and many people find it a reminder that worship does not depend on the season.

A simple example: if Ramadan begins on a certain Gregorian date this year, it will begin about ten or eleven days earlier next year.

Why the start can differ by a day

The new moon may be visible in one country but not yet in another, because of weather, position on the earth and the time of day. Scholars and national authorities also use different methods. Some follow local sighting, some accept sighting reports from other regions, and some use astronomical calculation.

For this reason, the first day of Ramadan or Eid can differ by one day between countries, and sometimes within one country. The method is a matter of scholarly discussion. It is best to follow the announcement of the trusted authority or mosque in your area. If you are unsure, ask a qualified local scholar.

General information for learning, not a fatwa. For your own situation, ask a qualified scholar.

Sources

  • Quran 9:36
  • Quran 10:5
  • Quran 2:189
  • Sahih al-Bukhari (Book of Fasting)
  • Sahih Muslim (Book of Fasting)