The argument Islamic to CalendarChange converts between Western (Gregorian) dates and Islamic dates. This computes the Islamic date of January 1, 2000:

The Islamic calendar has the following months:

The above date is therefore the 24th of Ramadan, 1420.

The Western date for the beginning of Ramadan of the Islamic year 1420:

The Islamic year has fewer days than the Western year:

The Islamic calendar is purely lunar (time of month corresponds to phase of the moon) but does not keep track of seasons, since there is no leap month. The Islamic calendar moves backward with respect to the Western calendar; for example, the start of Ramadan in successive years:

A program that computes the first and last dates of Ramadan for a given Western calendar year for the first Ramadan beginning that year:

Note that Ramadan can overlap January 1, as in 2000:

There is also the possibility that two Ramadans begin in the same Western year, as in 1932. The program returns the first Ramadan beginning that year:

Ramadan of the following Islamic year also began in 1932:

Since the names and the numerical order of the Islamic months are not well known in the Western world, it is useful to have the list of names: