The Islamic date corresponding to a date in the gregorian calendar can be computed by the following rule, with a maximum error of one day: multiply 970,224 by the islamic year, divide by 6 decimal places (one million), and add 621.5774. The figure to the left of the decimal point is the year C.E, and the decimal fraction multiplied by 365 is the day of the year.
A major religious calendar is the Islamic calendar, a lunar one used in most muslim countries. It is reckoned from July 622 C.E (1 Muharram 1 H), the first day of the first month of the 'year of the hijra', or migration of the Prophet Muhammad (peace be upon him) from Makkah to Medina (which took place in September 622 C.E). The islamic year consists of 12 lunar months. Thirty years constitute a cycle in which the 2nd, 5th, 7th, 10th, 13th, 16th, 18th, 21st, 24th, 26th, and 29th years are leap years of 355 days; the others are common years of 354 days.