If you've ever wondered why Ramadan lands on a different date every year, or why an Islamic year is numbered so differently from the Gregorian one, the answer comes down to one thing: the Hijri calendar follows the moon, not the sun.
A lunar year, not a solar one
The Gregorian calendar most of the world uses day-to-day is solar — it's built around the roughly 365.25 days it takes Earth to orbit the sun. The Hijri calendar is lunar instead. Each month begins with a new crescent moon, and twelve of those months add up to about 354 days — around 11 days short of a full solar year.
That 11-day gap is why Islamic dates drift steadily earlier on the Gregorian calendar each year. Ramadan, Eid, and every other Islamic observance cycle slowly through all four seasons over roughly 33 years, rather than landing in the same month every time.
Where the "AH" comes from
Islamic years are marked AH, short for the Latin Anno Hegirae — "in the year of the Hijrah." The count starts from 622 CE, the year the Prophet Muhammad migrated from Mecca to Medina, an event significant enough in early Islamic history to become the calendar's fixed starting point.
Two ways to determine a new month
There are two broad approaches to deciding exactly when a Hijri month begins:
- Moon sighting (ru'yah): a new month starts once the crescent moon is physically observed, a method many mosques and local authorities still use.
- Tabular calculation: a fixed arithmetic rule that can compute a date for any day, past or future, without needing an actual observation. This is the method used throughout this site, because it lets us show Hijri dates and Ramadan calendars for future years like 2027.
The two methods usually agree, but can differ by a day, especially right at the start of Ramadan or Eid. That's normal — it isn't an error on either side, just two different ways of answering the same question.
Why it still matters day to day
Beyond religious observance, the Hijri calendar remains the everyday reference point across much of the Muslim world for things like personal milestones, historical dates, and cultural identity — which is exactly why a simple, reliable Hijri date belongs on the same page as prayer times and a daily Urdu couplet.