How does the Jewish Calendar Work?
The heart of the prudent acquires knowledge, And the ear of the wise seeks knowledge.
Proverbs 18:15
The Jewish calendar is based on an approximate average length of the moon’s orbit around the earth, this time length is called the “molad”. The length of a molad is about 29 and half days and 44 minutes. Only one day of the year requires any deep understanding of the Jewish calendar’s math, the Feast of Trumpet, which also called Rosh Hoshanna (Jewish New Year) in the Jewish calendar. All the other days are simple addition or subtraction from this date.
Summary of the math of the Jewish calendar
Here's a summary of the calculations for finding the date of the Rosh Hoshanna. Followed by the simple math for the dates for the other annual holy days.
1. Pick a Gregorian year (eg, ) and determine the Jewish year.
+ 3761 =
2. Count the number of months to the Jewish year. ()
12 months × years + (extra leap months) = total months
3. Multiply the number of months by the average Jewish measurement of a month.
months × 29.54 days (approx) = days
4. Count this many days to get to the date of the Feast of Trumpets for the year
9/7/3761 BCE + days =
5. Determine the dates of the other feasts for the year
The Feast of Trumpets is on Tishri 1, all other holy days are simple addition/subtractions from this date.
Feast of Trumpets (Tishri 1, Rosh Hoshanna, Jewish New Year)
Passover/Unleavened Bread (minus 163 days) ( is the 14th of Nissan, which is minus 164 days)
Pentecost (minus 113 days)
Atonement (plus 9 days)
Feast of Tabernacles (plus 14 days)
Is that all?
In summation, yes, that is the entirety of the calculations of the Jewish calendar for determining the annual holy days.
Is the Jewish calendar correct and accurate?
Are the dates for the Jewish calendar correct? The modern Sanhedrin believes the Jewish calendar is not accurate, and has a committee setup to determine how and when to fix it.
You can read about the accuracy of the Jewish calendar and test it yourself here: Accuracy of Jewish Calendar
You can read the entire math and logic of the Jewish calendar here: Math of the Jewish Calendar.
Demystifying the Jewish Calendar
The theory behind the math of the Jewish calendar is very simple, it is a counting of months from September 7th, 3761 BCE to the year you are interested in, using the molad (an approximate average of the moon’s orbit) for the length of the months.
Every math calculation is very basic (grade-school level) math that everyone can understand by viewing each step one at a time.
You can learn how to convert the first day of any Jewish year (day 1 of the Jewish month of Tishri) to a Gregorian date.