What is the Islamic / Hijri Calendar?

Because it is purely lunar, the Hijri year moves through the seasons. Observational practice and calculated systems can produce differences of a day in month starts.

How the calendar is structured

12 lunar months; about 354 or 355 days.

Where and why it is used

Region: Muslim communities worldwide. Primary context: Islamic religious observance and, in some places, official or cultural dating.

History and development

The system belongs to the Medieval to Modern layer of the archive. Its origin is summarized as Hijra era beginning 622 CE. CalculatorWiser separates historical reconstruction, religious observance, civil use, and modern technical standards so different systems are not treated as though they all work the same way.

Visual reference gallery

Conversion and accuracy notes

Some calendar systems can be converted deterministically with modern algorithms. Others depend on observation, local authority, historical reconstruction, or regional practice. CalculatorWiser marks those distinctions rather than presenting uncertain dates as exact.

Research trail

This entry is part of the research-backed World Calendar Archive. Primary research anchor for this entry: Unicode CLDR / Islamic calendar references.