I'm sure that it is possible, but you'll need to research to find an algorithm for doing the conversion and then implement it as a FileMaker calculation.
It may be helpful to know that if you were to enter 1/1/0001 into a FileMaker date field, its numerical value is 1. and January 2, 0001 has the numerical value of 2 and so forth... (Dates in FileMaker count the number of days since 12/31/0000.)
Has Excel function and Java calculation
The months of the Muslim year, by convention, have 29 and 30 days alternately. This means that the Hijra - or, more exactly, the Hizri-year contains exactly 354 days. The 8 hours, 48 minutes and 36 seconds difference (11/30 of a day) between this figure and the astronomical lunar year adds up to 11 days in every cycle of 30 years. These 11 days are inserted into the calendar by establishing leap years. Every period of 30 years, therefore, has 11 leap years of 355 days instead of 354. These are normally the 2nd, 5th, 7th, 10th, 13th, 16th, 18th, 21st, 24th, 26th, and 29th years of the 30-year cycle. The "leap day" which is added to these years is always assigned to the end of the month of Dhu al-Hijja, the month of the Hajj - the Muslim pilgrimage to Mecca - and last month of the year. In just the same way, the Gregorian calendar adds an extra day to February every four years.
Since the Hijri year is 11 days shorter than the Gregorian year, the beginning of each Hijri year falls 11 days earlier in the Gregorian calendar each year. Thus the Hijri year moves backward in relation to the Western calendar. This retrograde motion has an important consequence: Muslim festivals fall at different times each year, according to the Western calendar, although always, of course, in the same month of the Hijri year. Every 33 years, the months of the Muslim calendar make a complete backwards circuit of the seasons. This explains why the Hajj, for example, sometimes falls in midwinter and sometimes in summer. The months of the Hijri year, unlike the Gregorian year, bear no relation to the seasons.
The conversion of Gregorian to Hijri dates and vice-versa is no easy matter, particularly if one is trying to find the exact day. The matter is further complicated by the fact that the Gregorian calendar used now did not come into use until 1582 in Europe, and not until the early 18th century in England. Dates before then, therefore, must be calculated according to still another system: the Julian calendar. Given this final complication, the easiest way to find the correspondence between a Gregorian and a Hijri date is to refer to a table.
Converting years is much easier. A simple rule of thumb is that each Gregorian century equals approximately 103 Hijri years, and that, conversely, each 100 years of the Hijri calendar equals 97 years of the Gregorian. A useful benchmark is that the year 1300 A.D. corresponded with 700 A. H.