Hijri ↔ Gregorian Date Converter

The Hijri calendar is lunar: its year runs 354 or 355 days, about eleven days shorter than the Gregorian year — which is why Hijri dates drift forward against the seasons every year. This tool uses the Umm al-Qura table, a pre-computed astronomical table of month starts, so the same input always returns the same result without depending on an announcement.

Why your Hijri date differs from a colleague's

Two countries can print Hijri dates a day apart on the same day, because some adopt a computed astronomical table while others rely on visual sighting of the crescent — and sighting depends on location and weather. The gap is a difference of reference, not an arithmetic error. When a Hijri date appears in a document that crosses borders, name the reference explicitly.

Conversion algorithm

Conversion is done by translating to the Julian Day Number (JDN) as an intermediate, then from JDN into the target calendar. This achieves ±1 day accuracy versus the printed Umm al-Qura calendar for years after 1937 CE (1356 AH).

Gregorian → JDN → Hijri (and vice versa)

Worked example

Convert 12 May 2026 to Hijri:

1. Input: 2026-05-12 (Tuesday)
2. Bridge through Julian Day Number (JDN)
3. Result: 25 Dhu al-Qi'dah 1447 AH
4. Day: Tuesday

When you need it

• Reading a Hijri date on an incoming document and mapping it to your own schedule
• Finding the end of a fiscal year or contract anniversary written in Hijri
• Checking the weekday of a Hijri date before setting a meeting
• Verifying a shelf-life or warranty window written in both calendars

How the two calendars differ

The Hijri year is about 11 days shorter, so roughly 33 Gregorian years match 34 Hijri ones. Hijri months are always 29 or 30 days, while Gregorian months run 28 to 31. That is why you cannot convert a span of years by multiplying a constant — convert both dates, then subtract.