HEBREW CALENDAR

PART OF SERIES, "TRACKING TIME: BEHIND OUR CLOCK AND CALENDAR"

Author: Ken Klark L. Flores

Photo: Kelly Haddocks / Pinterest

Introduction

The Hebrew calendar, also known as the Jewish calendar, is a lunisolar system, meaning months are based on lunar cycles while years align with the solar year to ensure holidays occur in the correct seasons. The current Hebrew year is AM 5786, which began at sunset on September 22, 2025, and will end at sunset on September 11, 2026. 

Origins

This calendar has has ancient lunisolar origins rooted in biblical mandates and agricultural cycles, which evolved over centuries from observation-based methods to a fixed, mathematically calculated system. (CALENDAR, HISTORY of - JewishEncyclopedia.com, 2021). The fundamental principles of the Hebrew calendar are found in the Bible, primarily in Genesis and Exodus (MDiv, 2023).

The calendar was designed to follow both the cycles of the moon (for months) and the sun (for seasons and the year). A day was defined as running from sunset to the next sunset, based on the creation narrative in Genesis ("And there was evening and there was morning, one day"). In the Book of Exodus, God commanded Moses that the month of Aviv (later called Nisan), which marks the beginning of spring and the Exodus from Egypt, would be the first month of the year.  In the early period, the start of a new month was determined by the physical sighting of the new crescent moon by witnesses, whose testimony was verified by the Sanhedrin (the Jewish high court) (Bradshaw, 2023). The decision of when to add an extra, or intercalary, month to keep the lunar calendar aligned with the solar year and ensure holidays like Passover occurred in the spring was also based on observations, such as the readiness of the barley crop  (Introduction to the Jewish Calendar, n.d.).

During the Babylonian exile in the 6th century BCE, the Jewish people adopted the Babylonian-Aramaic names for the months (e.g., Nisan, Sivan, Tishrei), which replaced the former numbered months. Following the destruction of the Second Temple in 70 CE, the ability of the Sanhedrin to convene and rely on observation became difficult. This led to a gradual shift toward a mathematically calculated calendar (Ben-Dov, 2025; Grinberg, 2023).

The modern, fixed Hebrew calendar was established by the sage Hillel II around 359 CE (Anno Mundi 4119). This new system standardized the length of months and introduced a fixed cycle for adding leap months, eliminating the need for physical observation (Steinmeyer, 2025). The fixed calendar uses the 19-year Metonic cycle, in which an extra month (Adar II) is added in seven specific years of the cycle to synchronize the lunar months with the solar year. The current year numbering system, known as Anno Mundi (AM, "year of the world"), was also established in the post-Talmudic period. This system calculates the years from a traditional date of Creation, which corresponds to sunset on October 6, 3761 BCE, in the Gregorian calendar. 

Components

The week has a cycle of seven days, from Sunday (Day 1) to Shabbat (Saturday, the day of rest). The days are referred to by number, except for Shabbat (About the Hebrew Calendar | Yale University Library, n.d.). A standard lunar year of 12 months is about 354 days, roughly 11 days shorter than the solar year. To prevent the holidays from drifting through the seasons (e.g., Passover occurring in winter), an extra month is added in a "leap year". Hebrew years can be "deficient" (353 or 383 days), "regular" (354 or 384 days), or "complete" (355 or 385 days). This variability is achieved by adjusting the length of the months Cheshvan and Kislev and through complex "Rosh Hashanah postponement rules" (deḥiyyot) that ensure holidays do not fall on certain inconvenient days of the week (Jewish Religious Year | Cycle, Holidays, & Facts, n.d.).

The months are 29 or 30 days long, starting approximately with the new moon's appearance. There are typically twelve months, but a leap month is added periodically. Tishrei (Sept–Oct), Cheshvan (Oct–Nov), Kislev (Nov–Dec), Tevet (Dec–Jan), Shevat (Jan–Feb), Adar (Feb–Mar), Adar I (only in leap years), Nisan (Mar–Apr), Iyar (Apr–May), Sivan (May–June), Tammuz (June–July), Av (July–Aug), and Elul (Aug–Sept) (The Jewish Calendar: A Closer Look - Judaism 101 (JewFAQ), 2024).

Use

The Hebrew calendar is used for Jewish religious observance and as an official calendar in Israel for both religious and civil purposes. Its uses include determining the dates of Jewish holidays and festivals, setting religious rituals and prayer times, and providing a framework for commemorative dates like Israel's Independence Day. It also serves civil functions in Israel, where it is printed on official documents and used in media alongside the Gregorian calendar (Jewish Calendar – Hebrew Calendar, n.d.).

Reference

CALENDAR, HISTORY OF - JewishEncyclopedia.com. (2021). Jewishencyclopedia.com. https://www.jewishencyclopedia.com/articles/3920-calendar-history-of

MDiv, R. L. (2023, July 5). In Search of the Original Hebrew Calendar. Biblearchaeology.org. https://biblearchaeology.org/abr-projects/the-daniel-9-24-27-project-2/5065-in-search-of-the-original-hebrew-calendar

Bradshaw, L. (2023, September 17). All about the Jewish Calendar. Familysearch.org. https://www.familysearch.org/en/blog/jewish-hebrew-calendar

Introduction to the Jewish Calendar. (n.d.). Www.chabad.org. https://www.chabad.org/library/article_cdo/aid/55194/jewish/Introduction.htm

Ben-Dov, J. (2025, June 30). The Calendar in the Hebrew Bible - Bible Odyssey. Bible Odyssey. https://www.bibleodyssey.org/articles/the-calendar-in-the-hebrew-bible/

‌Grinberg, T. (2023, August 3). The Jewish Calendar: It’s Complicated - Beth Israel Vancouver. Beth Israel Vancouver. https://www.bethisraelvan.ca/beth-israel-media/reflections-on-the-jewish-calendar-and-its-holidays/the-jewish-calendar-its-complicated/

Steinmeyer, N. (2025, September 26). Understanding the Jewish Calendar. Biblical Archaeology Society. https://www.biblicalarchaeology.org/daily/understanding-the-jewish-calendar/

The Jewish Calendar: A Closer Look - Judaism 101 (JewFAQ). (2024). Jewfaq.org. https://www.jewfaq.org/jewish_calendar_calculation

‌About the Hebrew Calendar | Yale University Library. (n.d.). Web.library.yale.edu. https://web.library.yale.edu/cataloging/hebraica/about-hebrew-calendar

Jewish religious year | Cycle, Holidays, & Facts. (n.d.). Encyclopedia Britannica. https://www.britannica.com/topic/Jewish-religious-year

‌Jewish Calendar – Hebrew Calendar. (n.d.). Www.timeanddate.com. https://www.timeanddate.com/calendar/jewish-calendar.html

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