What is the tabular Islamic calendar?

The tabular calendar is a fixed arithmetic scheme where 11 of every 30 years are leap years with 355 days instead of 354. It avoids the need for moon sightings and is fully predictable, which makes it ideal for software and historical conversion.

Why might the date differ from the one announced locally?

Religious observance often relies on the actual sighting of the new crescent moon, which can fall a day before or after the arithmetic prediction depending on location and weather. So Ramadan or Eid announced by a mosque may differ from the tabular date by up to a day.

When does the Hijri calendar begin?

The epoch is 1 Muharram of year 1 AH, which in this tabular scheme corresponds to 19 July 622 in the proleptic Gregorian calendar (16 July 622 in the Julian calendar). AH stands for Anno Hegirae, the year of the Hijra.

How long is a Hijri year?

A Hijri year is 12 lunar months totalling 354 or 355 days, about 11 days shorter than a solar year. That is why Islamic dates such as Ramadan move earlier through the Gregorian seasons by roughly 11 days each year.

Are the month lengths fixed?

In the tabular calendar odd-numbered months have 30 days and even-numbered months have 29, except the twelfth month Dhu al-Hijjah which gains a day to 30 in leap years. The true lunar calendar instead lets each month run 29 or 30 days based on the moon.

Gregorian ↔ Hijri Date Converter

The Islamic Hijri calendar is purely lunar, so its dates drift through the Gregorian seasons by about 11 days each year. This converter maps dates between the two systems with the widely used tabular (arithmetic) algorithm, which is deterministic and matches the calendars built into most software.

How it works

Both dates are converted through the chronological Julian Day Number (JDN), then into the target calendar:

Gregorian (y,m,d) ─► JDN ─► Hijri (y,m,d)
Hijri     (y,m,d) ─► JDN ─► Gregorian (y,m,d)

The Hijri side uses the standard 30-year cycle in which years 2, 5, 7, 10, 13, 16, 18, 21, 24, 26 and 29 are leap years of 355 days; the rest have 354. Odd months are 30 days, even months 29, with Dhu al-Hijjah taking the extra leap day.

Example and tips

Converting 2000-01-01 returns 24 Ramadan 1420 AH, and 2026-06-06 returns 20 Dhu al-Hijjah 1447 AH. Because observance depends on the sighting of the crescent moon, the start of Ramadan or the date of Eid announced where you live may differ from the tabular result by a day in either direction — treat the converted date as the calendrical reference, not a religious ruling.