On Which Days Do Jewish Holidays Begin?

Days on Which Jewish Holidays Can Occur

The Days of the Week When Passover Can Begin

Due to the structure of the Hebrew calendar, the first Seder can be on Friday night, Saturday night, Monday night or Wednesday night. This means that the first day of Passover (the next morning) can be Shabbat, Sunday, Tuesday or Thursday.

Conversely, the first Seder is never held on Sunday night, Tuesday night or Thursday night, and the first day of Passover is never Monday, Wednesday or Friday.

This gives rise to the common mnemonic Lo bedu Pesach (לא בד"ו פסח), Passover (Pesach) never starts on bedu, an acronym for bet (Monday), dalet (Wednesday) or vav (Friday).

The Days of the Week When Shavuot Can Begin

Shavuot comes exactly seven weeks after the second day of Passover. Thus if Passover begins on Sunday, Shavuot will begin on Monday.

As such, Shavuot can begin at sundown on Saturday, Sunday, Tuesday or Thursday, which means that the first day of the holiday can be Sunday, Monday, Wednesday or Friday.

Conversely, Shavuot never begins on Monday, Wednesday or Friday nights, which means that the first morning of Shavuot is never Tuesday, Thursday, or Shabbat.

And like Passover, there is a mnemonic for this as well: Lo gehaz Shavuot (לא גה"ז שבועות), Shavuot does not start on gimmel (Tuesday), hey (Thursday) or zayin (Shabbat).

The Days of the Week When Rosh Hashanah Can Begin

The first day of Rosh Hashanah is always the same day of the week as the third day of Passover. As such, Rosh Hashanah can begin at sundown on Sunday, Monday, Wednesday or Friday, which means that the first day of Rosh Hashanah can be Monday, Tuesday, Thursday or Shabbat.

Conversely, Rosh Hashanah never begins on Shabbat, Tuesday or Thursday nights, which means that the first morning of Rosh Hashanah is never Sunday, Wednesday or Friday.

And, you guessed it, there is a mnemonic for this as well: Lo adu Rosh (לא אד"ו ראש), Rosh Hashanah does not start on aleph (Sunday), dalet (Wednesday) or vav (Friday).

Once you know the day Rosh Hashanah is celebrated, you can quickly calculate that Yom Kippur is exactly one week after the day after Rosh Hashanah.

Thus, if Rosh Hashanah is on Monday and Tuesday (for example), Yom Kippur will be on Wednesday (beginning at sundown on Tuesday).

Also note that Sukkot and Shemini Atzeret both begin on the same day of the week as Rosh Hashanah, so calculating when they fall out is a cinch.

At Bash: Calculating the Entire Year

Once you know the day of the week when Passover begins in any given year, you can then calculate when many (but not all) of the year’s holidays will be celebrated. This is done by way of a simple system known as at bash, in which the first letter (aleph) is paired with tav (the final letter), and the second letter (bet) is associated with the penultimate letter (shin), etc.

We can then get the following handy series of hints:

Aleph (the first day of Pesach) is celebrated on the same day of the week as tav, (17 Tammuz and) Tisha B’Av

Bet (the second day of Passover) tells us when we will celebrate shin, Shavuot

Gimmel (the third day) lets us know the day of resh, Rosh Hashanah (and Sukkot and Shemini Atzeret)

Dalet (day four) foreshadows the day of the week for kuf, which stands for kriah (“reading”), an allusion to Simchat Torah, when the Torah reading cycle begins and ends in the Diaspora

Hay (day five) corresponds to tzaddi, tzom, the fast day of Yom Kippur

Vav (day six) reminds us on which day we just celebrated Purim (which begins with pei), five weeks earlier.

Zayin (day seven) pairs up with ayin, standing for etzim (“wood”), the upcoming minor holiday of the 15th of Av, which (among other things) marked the end of the season of cutting wood for the Temple altar.

(There are no hints telling us when we will celebrate the upcoming holidays of Purim and Chanukah, since the intervening months of Cheshvan and Kislev do not always have the same amount of days each year—and Purim sometimes comes after an extra month of Adar has been inserted into the calendar.)