How the Hebrew calendar works

The Hebrew (Jewish) calendar is lunisolar: its months follow the cycles of the moon, while the year is kept aligned with the solar seasons by periodically adding a leap month. That's why Jewish holidays fall on the same Hebrew date every year but land on a different date on the secular calendar, and why Passover always arrives in spring and Sukkot in autumn. Once the lunisolar mechanics click, the whole rhythm of the Jewish year, and every date you'll ever need to look up, makes sense.

How does a lunisolar calendar work?

• Months follow the moon. Each Hebrew month begins around the new moon, at Rosh Chodesh, and runs 29 or 30 days. A lunar year of twelve such months is about 11 days shorter than a solar year.
• Leap years add a month. Left alone, that 11-day drift would eventually push Passover into winter, so a 13th month, Adar II, is added in 7 of every 19 years, keeping the calendar's months anchored to their seasons.
• The result: a holiday's Hebrew date never moves, but its position on the secular calendar shifts year to year, sometimes by weeks.

Compare that to a purely lunar calendar, like the Islamic calendar, which has no leap month and so drifts through all four seasons over about 33 years. The Hebrew calendar's leap-month system is the specific fix that keeps Jewish holidays seasonal.

What are the Hebrew months? Because the weekly Torah reading and every daily learning cycle run on this same calendar, knowing the month you're in also tells you roughly where the yearly parsha cycle and the holiday season stand, without checking a separate reference.

The twelve months, in calendar order starting from Nisan, are Nisan, Iyar, Sivan, Tammuz, Av, Elul, Tishrei, Cheshvan, Kislev, Tevet, Shevat, and Adar (split into Adar I and Adar II in a leap year). Each carries its own character: Nisan opens with Passover, Sivan brings Shavuot, Tishrei holds the High Holy Days and Sukkot, Kislev brings Chanukah, and Adar carries Purim. Civil counting actually starts the year at Tishrei (Rosh Hashanah), even though Nisan is counted as the first month in the Torah, since the Exodus is treated as the start of the Jewish nation's own calendar.

How does the 19-year leap cycle work?

The Hebrew calendar runs on a fixed 19-year pattern: years 3, 6, 8, 11, 14, 17, and 19 of the cycle are leap years with an extra month. Over 19 years, 12 regular years of 12 months plus 7 leap years of 13 months keep the lunar count and the solar seasons in step to within a couple of hours. That precision is why a holiday's Hebrew date, say the 15th of Nisan for the first Seder, doesn't drift through the seasons the way it would on a calendar without leap months, even across many centuries.

Why do Jewish holidays "move" every year?

They don't move on the Hebrew calendar. Passover is always the 15th of Nisan; that never changes. It only looks like movement because you're watching two different clocks: the fixed, lunisolar Hebrew calendar underneath, and the solar Gregorian calendar most people check first. The leap-month system is precisely what keeps that apparent drift small and seasonal, instead of letting Passover wander across the whole year the way it does on a purely lunar calendar. In a non-leap year, a holiday can appear about 11 days earlier on the secular calendar than the year before; in a leap year, it jumps back later by roughly 18 to 19 days to compensate.

When does the Hebrew day begin?

One more piece that trips people up: a Hebrew date doesn't begin at midnight. It begins at sunset the evening before, following the Torah's own description of a day as "evening and morning." That's why Shabbat and every Jewish holiday start the night before the date most calendars print, and why an event on "the 15th of Nisan" is already underway by Thursday evening if the 15th falls on a Friday. Any Hebrew date converter, including Derekh Learning's, builds this evening start into its calculations automatically.

What year is it on the Hebrew calendar?

Hebrew years are counted from a traditional reckoning of creation (Anno Mundi), not from a historical or scientific starting point, the way the Gregorian calendar counts from a fixed reference year. Rosh Hashanah is both the new year and the day the year number advances: for example, Rosh Hashanah 5787 began at sundown on September 11, 2026, marking the start of the Hebrew year 5787. Because the Hebrew year turns over in the autumn rather than in January, a single Gregorian year always overlaps two consecutive Hebrew years.

Finding your own dates on the Hebrew calendar

Once you know the mechanics, the useful next step is converting your own dates. Derekh Learning's Hebrew date converter turns any birthday, anniversary, or event into its Hebrew date and back, in either direction. Two places this matters most:

• Yahrzeit, the annual Hebrew-date anniversary of a loved one's passing. Because the Hebrew and secular calendars don't move together, a yahrzeit lands on a different secular date each year, which means it slips past unnoticed unless you're tracking the Hebrew date directly. Look up or track a yahrzeit.
• B'nai mitzvah timing, a bar or bat mitzvah falls on the Hebrew birthday, not the secular one, and the parsha read that Shabbat depends on where the yearly Torah cycle happens to be that year. Find the parsha for a bar or bat mitzvah date.

Learn the year with Derekh Learning

Derekh Learning's daily learning follows the real Hebrew calendar: the holidays, the weekly parsha, zmanim, and every daily learning cycle described above, in a voice that fits you, so the calendar is never a separate thing you have to check on your own. See today's date on the Hebrew calendar and what's being learned right now, or start learning to see how the calendar shapes your very first lesson.