About the Hebrew Calendar
The Jewish calendar, derived from the ancient Hebrew calendar, has remained unchanged since about AD 900. It is the official calendar of the modern state of Israel and is used by Jewish people throughout the world as a religious calendar. The starting point of Hebrew chronology is the year 3761 BC, the date for the creation of the world as described in the Old Testament. The Jewish calendar is luni-solar, based on lunar months of 29 days alternating with 30 days. An extra month is intercalated every 3 years, based on a cycle of 19 years. Dates of the Jewish calendar are designated AM (Latin anno mundi,"the year of the world") and BCE (before the Common Era).
"Calendar," Microsoft® Encarta® Online Encyclopedia 2000
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Formula for converting Hebrew Dates to Gregorian Dates:
1) Using gematria, add the letters of the Hebrew date together.
2) Add 1240 to the number you get.
NOTE- The Jewish year begins in the middle of the Gregorian year, causing any Jewish year to correspond to two consecutive Gregorian years. The 1240 formula gives you the latter of the two years.
To see a display of the year in Hebrew and Gregorian months and days, type the Hebrew year into a browser search engine (e.g. ה'תשל"ה -- it is not necessary to include the initial ה in the search string). There will be a Hebrew Wikipedia hit, select it, and then scroll down to the calendar view.