The Hijri (Islamic lunar) calendar has 12 months, 354 or 355 days per year, with months that begin at the new crescent moon. Different communities determine month-start in different ways:
- Local moon sighting — a community sights the new crescent visually. This is the practice of many traditional jurists and is followed in much of the Muslim world.
- Astronomical calculation (Umm al-Qura) — the Saudi calendar uses calculated visibility of the moon at the meridian of Mecca. Most Saudi-aligned communities follow this.
- Tabular calendar (Ic, Friday epoch) — a fixed mathematical formula. Months alternate 30/29 with leap-year adjustments. Used by software when astronomical data is not available.
QiblaWeb uses the tabular calendar for date display and conversion. It is deterministic, fast, and runs without external data. It can differ from local moon sighting by ±1 day and from Umm al-Qura by 0–2 days. Every Hijri page on the site shows a disclaimer to that effect.
Why this matters for Ramadan
The first day of Ramadan and the day of Eid often vary by 1 day across communities. QiblaWeb publishes a tabular start date for planning purposes; for the actual fast and Eid, follow your local community.
Source
Calendar variants summarised from AlAdhan Islamic Calendar (retrieved 2026-05-09).