A purely lunar calendar of twelve months, drifting about eleven days a year against the Gregorian.
The Hijri calendar counts twelve lunar months and makes no attempt to stay aligned with the solar year. A lunar year is roughly 354 days, so every Islamic date moves about eleven days earlier in the Gregorian calendar annually and completes a full circuit of the seasons in about thirty-three years.
This is the single largest reason a holiday calendar cannot be copied from one year to the next. Ramadan is not in spring; Ramadan moves.
Most Hijri dates in this corpus carry a precision of estimate rather than exact, and that is not a weakness in the sourcing. The month begins on the sighting of the new crescent, and whether it is sighted is a question that cannot be settled in advance.
Both of these are the same Hijri date, observed in different countries, and both are recorded as estimates because the month's start depends on a sighting.
| 🇧🇳 | Wednesday 6 January 2027Brunei | Israk Mikraj27 Rajab. Recorded as an estimate. |
| 🇩🇯 | Wednesday 6 January 2027Djibouti | Isra and Mi'rajThe same occasion, the same estimated date. |
A lunisolar calendar inserts a month to stay with the seasons. The Hijri calendar does not, which is why it drifts through them.
Iran's Solar Hijri calendar shares the Hijri epoch and is solar, so it does not drift. Same starting point, different arithmetic.
See also lunisolar calendar · solar hijri calendar · moon sighting · precision
We hold this as rule_type: hijri_date — 363 rules. See what we hold.