ISLAMIC CALENDAR GUIDE
Understand the Hijri calendar
How lunar months work, when an Islamic day begins, why date conversions vary, and how to use Islamic dates with clarity and confidence.
Quick answer: The Hijri calendar has twelve lunar months of 29 or 30 days. Its year is about 10–11 days shorter than a solar year, and an Islamic date begins at sunset.
THE BASICS
A calendar shaped by the moon
The Islamic—or Hijri—calendar organizes the year into twelve lunar months. Each month follows a lunar cycle and contains either 29 or 30 days. A common Hijri year therefore contains 354 days, while some calculated calendar systems assign 355 days to a leap year.
Unlike calendars adjusted to remain aligned with the seasons, the Hijri calendar does not add a leap month. Ramadan, Hajj, and other observances consequently move through the seasons over a cycle of roughly 33 solar years.
At a glance
12
lunar months
29 or 30
days in each month
354–355
days in a calculated Hijri year
HOW TIME IS COUNTED
The rhythm of an Islamic date
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The day begins at sunset
In Islamic usage, the night precedes the daylight portion. Friday night begins at sunset on Thursday, and the first night of Ramadan begins before its first fasting day.
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The month follows the crescent
Ritual months are established according to the adopted sighting or calendar method. If the crescent is not established, the current month is completed as thirty days.
12
The year advances faster
Because a Hijri year is shorter than a Gregorian year, an annual Islamic date generally occurs about 10–11 days earlier in the following solar year.
DAYS OF THE WEEK
The week in Arabic and English
Arabic weekday names preserve a simple numerical pattern from Sunday through Thursday. Friday is named for congregational gathering, while Saturday is associated linguistically with cessation or rest.
| English | Transliteration | Arabic | Name or origin |
|---|---|---|---|
| Sunday | Yawm al-Ahad | يوم الأحد | The one / first |
| Monday | Yawm al-Ithnayn | يوم الإثنين | The two / second |
| Tuesday | Yawm al-Thulatha | يوم الثلاثاء | The three / third |
| Wednesday | Yawm al-Arbi‘a | يوم الأربعاء | The four / fourth |
| Thursday | Yawm al-Khamis | يوم الخميس | The fifth |
| Friday | Yawm al-Jumu‘ah | يوم الجمعة | Congregation / gathering |
| Saturday | Yawm al-Sabt | يوم السبت | Cessation / rest, linguistically |
On smaller screens, swipe horizontally to explore the complete table.
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A day runs from sunset to sunset
Thursday sunset begins the Islamic night belonging to Friday. Daylight Friday follows, and that Islamic day ends at the next sunset.
Weekly significance
Friday: Yawm al-Jumu‘ah is the weekly congregational day. Adult Muslim men who meet the conditions attend the Friday prayer; all Muslims should honor the day through lawful Sunnah practices and remembrance.
Monday and Thursday: Voluntary fasting on these days is established in the Sunnah, without making it obligatory.
Saturday: Its Arabic name does not establish an Islamic Sabbath or a general requirement to cease lawful work.
Calendar layout: Modern calendars may display Sunday, Monday, or Saturday first. Column order does not change the religious virtue of Friday or create a binding theological “first weekday.”
THE HIJRI ERA
Why years are counted from the Hijrah
The calendar era commemorates the Prophet Muhammad’s ﷺ migration—the Hijrah—from Makkah to Madinah. This event marked the formation of the Muslim community in Madinah and a decisive transition in Islamic history.
During the caliphate of Umar ibn al-Khattab (ra), Muslims formally adopted a consistent year-numbering system. The Hijrah was chosen as its epoch, and Muharram was retained as the first month of the year.
An important distinction
The Prophet’s ﷺ migration did not take place on 1 Muharram. The year of the Hijrah was selected as the calendar’s starting era, while Muharram remained the conventional beginning of the year.
You may see years written as AH, meaning “in the year of the Hijrah,” or simply H. Dates before the epoch may be described as BH—before the Hijrah.
ONE DATE, DIFFERENT RESULTS
Why Hijri–Gregorian conversions can vary
A conversion is only as exact as the calendar method, location, and date status behind it.
Observed calendars
A month begins after a valid crescent sighting or an authority’s determination. Geography and accepted testimony can lead to regional differences.
Calculated civil calendars
A fixed mathematical rule assigns 29- and 30-day months, often for administration, historical conversion, or software. It may not match a later observation.
Visibility-based forecasts
Astronomical criteria estimate where the crescent might be visible. These are valuable predictions but are not themselves reports of an actual sighting.
Local time and sunset
The same civil moment may fall on different Hijri dates in different locations, especially around sunset and the beginning of a new month.
USING ISLAMCAL
Read the status before relying on a date
Planning dates and confirmed religious dates serve different purposes. IslamCal labels important entries so you can see the basis immediately.
Confirmed — formally established by the stated authority for the stated audience or place.
Calculated — generated by a named mathematical calendar or criterion.
Estimated — useful for planning but subject to change.
Locally observed — based on a sighting or decision for a stated community.
PRACTICAL GUIDE
Which dates can you plan in advance?
Generally predictable
Calculated date ranges, historical anniversaries, educational schedules, and approximate seasonal planning can be prepared well in advance—provided they are labeled as estimates where appropriate.
Confirm near the date
The start and end of Ramadan, Eid al-Fitr, the beginning of Dhu al-Hijjah, and Eid al-Adha should follow the determination recognized by your community or authority.
Ask when it matters
For vows, waiting periods, zakat anniversaries, make-up fasts, travel across regions, or other personal rulings, consult a qualified scholar who understands your circumstances.
COMMON QUESTIONS
Helpful calendar details
Is Friday the first day of the Islamic week?
Friday is the weekly congregational day and carries special virtue, but sources and modern calendars differ on which weekday is displayed first. This does not change Friday’s religious status.
Are all four sacred months consecutive?
No. Dhu al-Qadah, Dhu al-Hijjah, and Muharram are consecutive; Rajab occurs separately.
Does every Muslim country use the same date?
No. Countries and communities may follow different religious authorities or calendar policies.
Key terms
Hijri: relating to the calendar era of the Hijrah.
Hilal: the early visible crescent associated with a new lunar month.
Ru’yah: sighting or observation.
Hisab: calculation.
Conjunction: the astronomical alignment commonly called the new moon; it is not the same as a visible crescent.
Ikhtilaf al-matali‘: differing lunar horizons or regions of visibility.
Continue through the Islamic year
Explore the meaning, significance, key dates, and Sunni guidance for each of the twelve months.