Overview of the Hebrew Calendar
The Hebrew calendar (הַלּוּחַ הָעִבְרִי) is a lunisolar calendar that has been used by Jewish communities for religious purposes for over 2,000 years. It coordinates lunar months with the solar year using the 19-year Metonic cycle, ensuring that festivals remain in their appropriate seasons.
Year Count
Years are counted from the traditional date of creation — Anno Mundi (AM). The year 2025 CE corresponds to the Jewish year 5785–5786 AM. The year begins on Rosh Hashanah (the 1st of Tishrei), which falls in September or October of the Gregorian calendar.
Structure
The Hebrew calendar has 12 months in a regular year and 13 in a leap year (7 leap years in every 19-year cycle):
- Nisan, Iyar, Sivan, Tammuz, Av, Elul (spring/summer)
- Tishrei, Cheshvan, Kislev, Tevet, Shevat, Adar (fall/winter)
- In a leap year, Adar is split into Adar I and Adar II
The months Cheshvan and Kislev can vary between 29 and 30 days to prevent major holidays from falling on certain weekdays, making the Hebrew calendar especially sophisticated.
Major Holidays
- Rosh Hashanah: Jewish New Year, 1–2 Tishrei
- Yom Kippur: Day of Atonement, 10 Tishrei — the holiest day
- Sukkot: Feast of Tabernacles, 15 Tishrei
- Hanukkah: 25 Kislev (8 days)
- Purim: 14 Adar
- Passover (Pesach): 15 Nisan — must fall in spring
- Shavuot: 6 Sivan — 50 days after Passover
The Seven-Day Week and Shabbat
The Hebrew week runs Sunday through Saturday, with Shabbat (the Sabbath) observed from Friday sunset to Saturday nightfall. This seven-day cycle, inherited by Christianity and Islam, forms the basis of the global work week. The Hebrew calendar carefully arranges months so that Yom Kippur never falls on a Friday or Sunday, and Hoshana Rabbah never falls on a Shabbat.
Calculation vs. Observation
Since the 4th century CE, the Hebrew calendar has been based entirely on mathematical calculation rather than direct moon sighting — a remarkable feat of ancient astronomy that allows Jewish communities worldwide to observe holidays on the same day.