Calculation method — Hijri calendar

Why this calendar, and why Nassî' ?

This calendar is built on the "Fateh" astronomical calculation, a luni-solar system based on the 19-year Metonic cycle (19 solar years = 235 lunar months). Within this cycle, seven years are embolismic: they count 13 months instead of 12, through the insertion of an intercalary month, "Nassî'", between Rabi' al-Awwal and Rabi' al-Thani. This periodic correction keeps the start of the year anchored near spring, year after year, instead of drifting through the seasons as happens in the purely lunar Hijri calendar used today, which advances by about 11 days every solar year.

We reinstated the month of Nassî' on the basis that the Quran does not speak of abolishing the principle of intercalation itself, but rather condemns, in verse 37 of Surat At-Tawba, its political misuse: postponing or advancing the sacred months according to the interest of the moment, to declare war or a truce. This calendar is therefore an attempt to separate the rigorous astronomical adjustment of the sequence of months from that condemned political manipulation, while keeping the twelve original month names and their stable position within the cycle of the seasons.

The origin of the calendar

The starting point of the calendar is not arbitrary. It is set on the first lunation of Muharram of year 1 of the Hijra, between 621 and 622. This is the same origin as that of the Hijri calendar in use today and of the Persian calendar, which begin in the same year: the one is purely lunar, the other purely solar. The three calendars thus remain comparable. What sets them apart is the way the years are counted after this starting point: the usual Hijri calendar, by abolishing intercalation, lets its months drift through the seasons; the Persian calendar follows the sun without the lunar months; this one keeps the lunar months and, thanks to the Nassî', brings them back to spring.

The Quranic calendar

The Quranic calendar is the calendar as the people of Muhammad understood it when the revelation came down: twelve months of thirty days. Its units are the night (ليلة) and the period of ten days: each month is divided into three periods of ten days, numbered from "Day 1" to "Day 10". In this table, the day runs from midnight to midnight.

Twelve months of thirty days make 360 days. To keep up with the solar year, every year receives a Nassî' of five or six days, outside the periods of ten: six days when the year contains a 29 February, five otherwise.

Year 1 begins on 21 September 621 of the proleptic Gregorian calendar (that is 18 September 621 in the Julian calendar), and every year begins on 21 September. The astronomical computation of the equinox does not give a fixed day; a fixed date is safer for counting. 21 September lies next to the autumn equinox, and the Gregorian leap-year rule (97 years of 366 days in 400) keeps it close: the year does not drift through the seasons.

All days are counted as Julian day numbers, the same axis as the luni-solar calendar and the Gregorian calendar: every day of the Quranic calendar has its Gregorian date and its luni-solar date.

Order of the months:

1 Ramadan First month · fasting
2 Shawwal
3 Dhu al-Qa'da
4 Dhu al-Hijja
5 Muharram Inviolable month
6 Safar Inviolable month
7 Rabi' al-Awwal Inviolable month
8 Rabi' al-Thani Inviolable month
✦ Nassî' 5/6 days · outside the tens Inviolable month
9 Jumada al-Ula
10 Jumada al-Akhira
11 Rajab
12 Sha'ban

The inviolable period comprises Muharram, Safar, Rabi' al-Awwal, Rabi' al-Thani and always the Nassî', placed after Rabi' al-Thani to lengthen it. Ramadan, the first month of the year, opens on 21 September, near the autumn equinox; Rabi' al-Awwal begins near the spring equinox, and Sha'ban ends on the following 20 September.

Dates before Friday 15 October 1582 are given in the Julian calendar then in use (marked "Julian"), later ones in the Gregorian calendar: Thursday 4 October 1582 (Julian) is followed by Friday 15 October 1582 (Gregorian).

Quranic calendar →