In the Hebrew calendar the years are counted from the creation of the world, which is considered to have taken place 5760 years ago as of the year 2000. Days are reckoned from evening to evening. The Jewish civil year begins in September or October with the festival of Rosh Hashanah (the first day of Tishri).

The calendar is based on 12 or sometimes 13 lunar months that adjust to the solar year. The 12 months are Tishri, Kheshvan, Kislev, Tevet, Shevat, Adar, Nisan, Iyar, Sivan, Tammuz, Av, and Elul. The 3rd, 6th, 8th, 11th, 14th, 17th, and 19th years in every 19-year cycle have a 13th month. This extra month of 30 days, Adar II, is added after Adar.

The months and years of the Hebrew calendar do not correspond with the Gregorian calendar, which is the calendar in common use in the world today. The Gregorian calendar is based on the birth of Jesus Christ and uses the abbreviations a.d. (year of the Lord) and b.c. (before Christ). When Jews date events in accordance with the Gregorian calendar they use c.e. (common era) and b.c.e. (before the common era).

The Gregorian is a correction of the Julian calendar, which had been in use since 46 b.c.e. Leap years had been miscalculated in the Julian calendar; by 1582 the calendar was 10 days behind the solar year. Pope Gregory XIII corrected the calendar by dropping 10 days. The new calendar was adopted by the Catholic church in 1582 but at later dates in non-Catholic countries. Russia did not accept the new calendar until 1918. In Russia and part of Poland, the Julian calendar was generally used throughout the 1800s, when the difference had accumulated to 12 days. Polish vital records often give both the Julian and Gregorian dates. This can be confusing to beginning researchers. When both dates are given, use the later date (the Gregorian) for your record keeping.