How does the Islamic calendar work?
It depends on the moon, not the sun. The Islamic (Hijri) calendar has 12 lunar months of 29 or 30 days, and each month starts with the new crescent moon. A Hijri year is about 354 days, roughly 11 days shorter than the Gregorian year, so Ramadan and the two Eids move earlier every year.
The basics
Allah made the moon a clock for people. The phases are visible to everyone, in every country, without any special tools.
- Year count: from the Hijrah, the Prophet ﷺ's migration to Medina in 622 CE, written "AH".
- Month length: the Prophet ﷺ said the month is sometimes 29 days and sometimes 30 (Sahih al-Bukhari 1913).
- Day start: an Islamic day begins at sunset, so the night comes before its day. That's why the first taraweeh is prayed the evening before the first fast.
The 12 months
- Muharram (sacred; Ashura on the 10th)
- Safar
- Rabi al-Awwal
- Rabi al-Thani
- Jumada al-Ula
- Jumada al-Akhirah
- Rajab (sacred)
- Shaban
- Ramadan (the month of fasting)
- Shawwal (Eid al-Fitr on the 1st)
- Dhul Qadah (sacred)
- Dhul Hijjah (sacred; Hajj and Eid al-Adha on the 10th)
How a new month is decided
The Prophet ﷺ said to start fasting on seeing the crescent, stop on seeing it, and if the sky is overcast, complete thirty days (Sahih al-Bukhari 1909). Today Muslims follow a few approaches, and scholars differ on which is best:
- Local sighting: the moon must be seen in your own country or region.
- Following another country: some communities follow Saudi Arabia or the first reliable sighting anywhere.
- Astronomical calculation: some organizations, such as the Fiqh Council of North America, set dates in advance by calculation.
This is why mosques in the same city sometimes start Ramadan or celebrate Eid on different days. Both sides are trying to follow the sunnah. See Why do Muslims celebrate Eid on different days? and How do I know which day Eid is?
Why it matters in daily life
Because the year is shorter, Ramadan cycles through all seasons over about 33 years: short winter fasts, then long summer ones. For work and school, you'll often only know the exact Eid date a day or two ahead, so ask for time off with a flexible date. The new Hijri year begins on 1 Muharram. See Do Muslims celebrate the Islamic New Year?
- 12 lunar months of 29 or 30 days, about 354 days a year.
- Dates move about 11 days earlier each Gregorian year.
- Months begin with the new crescent; days begin at sunset.
- Communities differ on sighting versus calculation.
People also ask
How do I celebrate Eid with my kids?
Yes, make Eid the best day of the year for kids: countdowns, crafts, the Eid prayer, gifts, outings and simple words on its meaning.
Read the full answer →What is the Eid takbir and when do I say it?
Yes, it's a short chant glorifying Allah. Say it from the night before Eid al-Fitr until the prayer, and through Dhul Hijjah for Adha.
Read the full answer →Do Muslims celebrate the Islamic New Year?
No, not as a festival like Eid. The Islamic New Year (1 Muharram) has no set rituals, but many mark it quietly with reflection and dua.
Read the full answer →What is Ashura and should I fast on it?
Yes, fasting Ashura (10 Muharram) is sunnah and expiates a year of sins. Its link to Moses, fasting the 9th too, and the Shia observance.
Read the full answer →What can I do on Laylat al-Qadr if I'm on my period?
Yes, you can still do a lot on your period: dua, dhikr, istighfar, charity and listening to Quran. What you skip and scholars' views.
Read the full answer →