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Pesach on 15th of Nissan vs. the 14th

Why does Pesach begin on the 15th of Nisan when Numbers 28:16 says “And in the first month, on the fourteenth day of the month, is the LORD’S passover”?

Special thanks to Rabbi George Schlesinger for this guest post.

First of all, it’s helpful to know and understand the Hebrew and to know that in ancient days there were two sacrifices i.e. two holidays that were conjoined into one in later days. There was the Pascal sacrifice/Pascal holiday which was known as the “Pesach” or “passover.” This was an agricultural holiday celebrating springtime and the new lambs of the flock and it apparently preceded the Exodus from Egypt by many, many years. That sacrifice/holiday was on the 14th of Nisan. And it’s the term that in later days came to be used in Judaism for what was in ancient times a separate sacrifice/holiday celebrated a day later…the 15th of Nisan and the start of a 7 day festival during which matza was eaten. The holiday celebrating the Exodus is (in the Bible) usually called Chag HaMatzot or Festival of Matzah. So a more precise translation of verses 16 and 17 would read:

וּבַחֹ֣דֶשׁ הָרִאשׁ֗וֹן בְּאַרְבָּעָ֥ה עָשָׂ֛ר י֖וֹם לַחֹ֑דֶשׁ פֶּ֖סַח לַיהוָֽה׃

16) In the first month, on the fourteenth day of the month, there shall be a passover (pesach) sacrifice to the Lord

וּבַחֲמִשָּׁ֨ה עָשָׂ֥ר י֛וֹם לַחֹ֥דֶשׁ הַזֶּ֖ה חָ֑ג שִׁבְעַ֣ת יָמִ֔ים מַצּ֖וֹת יֵאָכֵֽל׃

17) and on the fifteenth day of that month a festival (chag). Unleavened bread shall be eaten for seven days.

To add just a little, I quote from the Jewish Publication Society’s commentary on the Book of Numbers on page 243:

“The day of the paschal offering and the seven-day Festival of Unleavened Bread are discrete holidays. Yet the fact that the paschal offering is mentioned even though it is a private sacrifice (see Exodus 12:1-11) –– and hence no description is given –– indicates that the two festivals are already fused.”

In later centuries, the two sacrifices were both made on the 14th of Nisan. The “pesach”/paschal offering earlier in the day than the offering for the Chag HaMatzot since that was the lamb that was to be eaten at the Seder commemorating the Exodus and it had to be slaughtered and roasted prior to sundown of the 15th so that it could be consumed during the Seder.


When do the Holidays begin?

In general, Jewish Holidays begin the evening before the date specified. This is because the Jewish day actually begins at sundown on the previous night. Sometimes, for clarity, the Erev holiday is also included to indicate that the holiday begins the evening before.

For example, in the April 2015 calendar below, Erev Pesach is listed as April 3rd and the first day of Pesach is listed as April 4th. This means that the holiday of Pesach begins on the evening on April 3rd.

And, Rosh Chodesh Iyyar is listed on April 19. This means that Rosh Chodesh begins on the evening of April 18, even though the Erev is not explicitly mentioned on the calendar.

April 2015

Sun Mon Tue Wed Thu Fri Sat
1 2 3









12 13 14 15 16

17 18


21 22


24 25
26 27 28 29 30

Minor fasts (Tzom GedaliahAsara B’TevetTa’anit EstherTa’anit Bechorot, and Tzom Tammuz) begin at dawn. Major fasts (Yom Kippur and Tish’a B’Av) begin the evening before.

Correction: Ta’anit Bechorot falls on Friday April 6, 2012

Ta’anit Bechorot (Fast of the Firstborn) falls on Friday, April 6, 2012. An earlier version of the calendar we publish incorrectly had this minor fast on Thursday.

When this fast day falls on Friday, we do in fact observe the fast on Friday, even though Shabbat follows immediately.

It is only in years when the date of the fast falls on Shabbat that the fast is moved. In this case, Ta’anit Bechorot is moved back to Thursday, because it is preferable not to fast immediately before Shabbat.

Source: Mishnah Berurah: the classic commentary to Shulchan Aruch Orach Chayim, comprising the laws of daily Jewish conduct, Volume V (B), Pesach. §470: “That the first-born fast on Erev Pesach.”

What is Havdalah (or, When does Shabbat end)?

Shabbat ends after sundown on Saturday night when there are three stars visible. Depending on latitude and longitude, this is usually between 42 and 72 minutes after sundown.

According to Wikipedia,

There are three widely observed practices, all of which have support in the halachic literature:

  • Appearance of three medium-sized stars in the sky (sun 7°5′ below the horizon, or 42 minutes after sundown), as in the Talmud. This is normative practice in Conservative Judaism. In Orthodox Judaism, this position is used widely for the end of rabbinical fasts, but less frequently for the end of Shabbat or biblical festivals.
  • Appearance of three small stars widely spaced in the sky (sun 8.5°-8.75° below the horizon): common practice in much of Orthodox Judaism [10]
    • “50 minutes after sundown” is actually a variant of this position. Rabbi Moshe Feinstein ruled this way because most people cannot easily calculate when “8.5° after sundown” will occur, and 8.5° takes 50 minutes at its longest, near the summer solstice, at the latitude of much of the United States.[2]
  • 72 minutes after sundown (“opinion of Rabbeinu Tam“): equivalent to other definitions of nightfall, and safe according to all opinions. Common practice in Chasidic and other Charedi communities

How does Hebcal determine anniversaries (birthdays, yahrzeits) in Adar, Cheshvan, or Kislev?

Calendrical CalculationsHebcal uses the anniversary algorithm defined in Calendrical Calculations by Edward M. Reingold and Nachum Dershowitz, which accords with Ashkenazic practice.


Reingold and Dershowitz write:

The birthday of someone born in Adar of an ordinary year or Adar II of a leap year is also always in the last month of the year, be that Adar or Adar II. The birthday in an ordinary year of someone born during the first 29 days of Adar I in a leap year is on the corresponding day of Adar; in a leap year, the birthday occurs in Adar I, as expected. Someone born on the thirtieth day of Marcheshvan, Kislev, or Adar I has his birthday postponed until the first of the following month in years where that day does not occur. [Calendrical Calculations p. 111]


Yahrzeit refers to the anniversary, according to the Hebrew calendar, of the day of death of a loved one. Alternative spellings include yahrtzeityortsaytyartzeit. Yahrzeit is written יאָרצײַט in Yiddish, which translates to “time of year”; the Hebrew equivalent is נַחֲלָה, transliterated as nachala (“legacy,” or “inheritance”).

The rules for a Yahrzeit are a little different than for a birthday:

The customary anniversary date of a death is more complicated and depends also on the character of the year in which the first anniversary occurs. There are several cases:

  • If the date of death is Marcheshvan 30, the anniversary in general depends on the first anniversary; if that first anniversary was not Marcheshvan 30, use the day before Kislev 1.
  • If the date of death is Kislev 30, the anniversary in general again depends on the first anniversary — if that was not Kislev 30, use the day before Tevet 1.
  • If the date of death is Adar II, the anniversary is the same day in the last month of the Hebrew year (Adar or Adar II).
  • If the date of death is Adar I 30, the anniversary in a Hebrew year that is not a leap year (in which Adar only has 29 days) is the last day in Shevat.
  • In all other cases, use the normal (that is, same month number) anniversary of the date of death.

[Calendrical Calculations p. 113]

Yahrzeit Example

For example, suppose Ploni ben Ploni passed away on 14 March 2001. That date corresponds to the 19th of Adar, 5761. Since 5761 was not a leap year, there was only one Adar that year (i.e. the date of death occurred in 12th month of the Hebrew year).

Suppose one wishes to observe the yahrzeit in Hebrew year 5765. Since 5765 is a leap year and none of the other rules applies, we use the same month number as the date of death. In a leap year the 12th month is Adar I, so the yahrzeit is observed on 19th of Adar I, 5765 (28 February 2005).


On page 114, Reingold and Dershowitz write:

There are minor variations in custom regarding the anniversary date in some of these cases. For example, Spanish and Portuguese Jews never observe the anniversary of a common-year date in Adar I.

There are undoubtedly many differing opinions regarding when to observe an Adar yahrzeit.

Here are two articles which offer differing opinions from our implementation:

For all matters of halacha, consult your local rabbi.


Reingold and Dershowitz cite two sources:

The Comprehensive Hebrew Calendar, Arthur Spier, 3rd edition, 1986, pp. 5-7

Talmudic Encyclopedia: A Digest of Halachic Literature and Jewish Law From The Tannaitic Period to the Present Time Alphabetically Arranged, vol I (1951), p. 93; vol. XXIII (1997), cols 153-154


9 Feb 2005: added errata at Nachum Dershowitz’s request.
9 Mar 2005: Added Ploni ben Ploni example.
9 Mar 2014: Added links to opinions by Rabbis Golinkin and Schachter
28 Dec 2016: Corrected misspellings
3 Feb 2021: Added “Sources” section