How the Hebrew Calendar Works
A guide to understanding Hebrew dates and how they align with the Gregorian calendar
Two calendar systems, one life
If you have ever looked at a Hebrew English calendar and wondered why Passover “moves” every year, or why some years have an extra month, you are not alone. The Hebrew calendar and the Gregorian calendar work on fundamentally different principles, and understanding the basics makes the whole system click.
Gregorian: solar. Hebrew: lunisolar.
The Gregorian calendar (the one most of the world uses day-to-day) is a solar calendar. Its year is based on the time it takes Earth to orbit the sun: approximately 365.25 days. Months are fixed lengths (28-31 days) and do not correspond to the moon.
The Hebrew calendar is lunisolar. It tracks both the moon and the sun. Each month begins at the new moon (roughly 29.5 days), so months alternate between 29 and 30 days. But since 12 lunar months add up to only about 354 days (11 days short of a solar year), the Hebrew calendar adds a leap month every few years to stay aligned with the seasons.
This is why Jewish holidays seem to “move” on the Gregorian calendar. They do not move on the Hebrew calendar at all. Passover is always 15 Nisan. But 15 Nisan falls on a different Gregorian date each year because the two systems measure time differently.
The Hebrew months
The Hebrew year has 12 months in a regular year and 13 in a leap year. The year begins in Tishrei (around September-October), when Rosh Hashanah falls.
| Month | Days | Approx. Gregorian | Key Holidays |
|---|---|---|---|
| Tishrei | 30 | Sep-Oct | Rosh Hashanah, Yom Kippur, Sukkot |
| Cheshvan | 29 or 30 | Oct-Nov | Length varies by year |
| Kislev | 29 or 30 | Nov-Dec | Hanukkah begins 25 Kislev |
| Tevet | 29 | Dec-Jan | |
| Shevat | 30 | Jan-Feb | Tu BiShvat on 15 Shevat |
| Adar | 29 | Feb-Mar | Purim on 14 Adar. In leap years: Adar I (30 days) + Adar II (29 days) |
| Nisan | 30 | Mar-Apr | Pesach begins 15 Nisan |
| Iyar | 29 | Apr-May | Lag BaOmer, Yom HaAtzmaut |
| Sivan | 30 | May-Jun | Shavuot on 6 Sivan |
| Tammuz | 29 | Jun-Jul | |
| Av | 30 | Jul-Aug | Tisha B'Av on 9 Av |
| Elul | 29 | Aug-Sep | Month of repentance before Rosh Hashanah |
Leap years and Adar II
A regular Hebrew year has 12 months and about 354 days. A leap year adds a 13th month called Adar II (or Adar Bet), bringing the year to about 384 days. This extra month keeps Passover in the spring, as the Torah requires.
Hebrew leap years follow a fixed 19-year cycle called the Metonic cycle. In every 19-year cycle, years 3, 6, 8, 11, 14, 17, and 19 are leap years (7 out of 19). In a leap year, the regular month of Adar is replaced by Adar I (30 days) followed by Adar II (29 days). Purim moves to Adar II.
How to read a Hebrew date
A Hebrew date is written as day month year. For example, 15 Nisan 5787 is the first night of Passover in the Jewish year 5787 (spring 2027 on the Gregorian calendar).
The Hebrew year count starts from the traditional date of creation. To roughly convert a Hebrew year to Gregorian, subtract 3760 (for dates before Rosh Hashanah) or 3761 (after Rosh Hashanah). So 5787 corresponds to 2026-2027.
When does the day begin?
On the Gregorian calendar, a new day starts at midnight. On the Hebrew calendar, a new day starts at sunset. This is why Jewish holidays “begin the evening before.” When you light Shabbat candles on Friday evening, it is already Saturday on the Hebrew calendar.
This difference matters when converting dates. An event that happens on Friday evening after sunset is on the same Gregorian day (Friday) but the next Hebrew day (Saturday). A good Hebrew English calendar handles this automatically.
Why use a bilingual calendar?
If you or your family observe Jewish holidays, track yahrzeits, or celebrate milestones on Hebrew dates, a bilingual calendar lets you see everything in one place. Instead of cross-referencing two separate calendars, you see “15 Nisan / April 2” at a glance.
For educators, a Hebrew English calendar in the classroom means students and parents can see both school dates and Jewish holidays together, without confusion.
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