How the Jewish Calendar Works

Lunar months adjusted to the solar year by a leap-month every two or three years — the calendar Hillel II formalized in 358/9 CE.

By The Editors

Calendar · 3 minute read

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Summary. The Jewish calendar is luni-solar: the months are lunar (29 or 30 days), beginning at the new moon; the year is adjusted to the solar cycle so that Pesach always falls in the spring (Devarim 16:1). A 19-year cycle includes seven leap years, in which a second month of Adar (Adar II) is added. The current year as of fall 2025 is 5786; from Rosh Hashanah 2026 onward, 5787. Months named: Nisan, Iyar, Sivan, Tammuz, Av, Elul, Tishrei, Cheshvan, Kislev, Tevet, Shevat, Adar (Adar I and II in leap years).

Lunar Months

Each Hebrew month begins at Rosh Chodesh — the new moon. The lunar cycle is approximately 29.5 days; months are alternately 29 and 30 days (with some variation). The lunar year of 12 months is approximately 354 days — 11 days shorter than the solar year. Without adjustment, the holidays would drift through the seasons (as they do in the Islamic Hijri calendar). The Torah's commandment that Pesach fall in the spring (chodesh ha-aviv, Devarim 16:1) requires adjustment.

The 19-Year Cycle

The Metonic cycle (named after the 5th-century BCE Greek astronomer Meton) of 19 solar years is approximately equal to 235 lunar months. Seven of those 19 years are leap years, each with a second Adar (Adar I and Adar II) inserted between Shevat and Nisan. The leap years in a cycle are years 3, 6, 8, 11, 14, 17, and 19. The current year (5786) is the 8th year of the cycle starting in 5779 — it is a leap year, with both Adar I and Adar II. The next leap year is 5789 (the 11th of the cycle).

Months and Their Holidays

Nisan (Mar–Apr): Pesach (15–22 Nisan).

Iyar (Apr–May): Yom HaShoah (27 Nisan, sometimes Iyar), Yom HaZikaron (4 Iyar), Yom HaAtzmaut (5 Iyar), Lag BaOmer (18 Iyar), Yom Yerushalayim (28 Iyar).

Sivan (May–Jun): Shavuot (6–7 Sivan).

Tammuz (Jun–Jul): 17th of Tammuz (fast).

Av (Jul–Aug): Tisha B'Av (9 Av), Tu B'Av.

Elul (Aug–Sep): Selichot begin; preparation for the Yamim Noraim.

Tishrei (Sep–Oct): Rosh Hashanah (1–2), Yom Kippur (10), Sukkot (15–21), Shemini Atzeret/Simchat Torah (22/23).

Cheshvan (Oct–Nov): Often called 'Mar Cheshvan' (bitter Cheshvan) because no holidays.

Kislev (Nov–Dec): Hanukkah begins (25 Kislev).

Tevet (Dec–Jan): Hanukkah continues; 10th of Tevet (fast).

Shevat (Jan–Feb): Tu BiShvat (15 Shevat).

Adar (Feb–Mar): Purim (14 Adar; Adar II in leap years).

The Year Begins Where?

Different things begin in different months. Nisan is the first month of the year for purposes of counting kings' reigns and festivals (Shemot 12:2). Tishrei is the first month for counting years from creation (Rosh Hashanah is in Tishrei). Elul is the first month for tithing animals. Shevat (specifically Tu BiShvat) is the new year for trees. The Mishnah (Rosh Hashanah 1:1) actually lists four new years.

Calendrical Tools

Hebcal.com is the standard online calendar; it provides parshah, holiday, and zmanim (halachic times) for any location. A printed luach (calendar) is the traditional tool; the Ezras Torah Luach and the OU Luach are widely used in Orthodox communities. Apps for iPhone and Android (Jewish Calendar, Daf Yomi, Hebcal) integrate the Jewish calendar with iPhone or Google Calendar.

Where Denominations Diverge

The calendar is universal across all denominations. Some Reform congregations observe one day of festivals even in the diaspora (vs. two in Orthodox and Conservative). Sephardic communities follow the same calendar as Ashkenazi.

Sources

Torah: Shemot 12:2; Devarim 16:1.

Mishnah, Rosh Hashanah 1:1.

Talmud Bavli, Rosh Hashanah 25a (Hillel II's calendar).

Rambam, Mishneh Torah, Hilchot Kiddush HaChodesh.