בס"ד

by Dr. Irv Bromberg, University of Toronto, Canada

[Click here to go back to the **Hebrew Calendar Studies** home page]

This page discusses rules for determining the regular weekly *Torah* portions (*parshiot*, or in the singular *parshah*), according to the rules followed by Orthodox Jews, intended to assist programmers who wish to implement an algorithm. My goal is to present the simplest possible rules in a comprehensive, unambiguous, top-down structured, strictly logical manner. Although a human with insight and experience might be able to determine the weekly *Torah* portion in fewer steps, especially by using table lookups, a computer program that follows these rules could arrive at the same answer in a fraction of a millisecond, for any date in the past, present or future.

This algorithm determines which *Torah* portions are combined, both in the diaspora and in Israel, for all 14 unique types of years on either the traditional Hebrew calendar or the Rectified Hebrew calendar (the rules are identical for both). The following table shows the "character" of each year type, indicated by 3 or 4 symbols, along with their exact frequencies in the full 689472-year repetition cycle of the traditional Hebrew calendar:

- A digit 2, 3, 5, or 7 denotes the first weekday of
*Rosh HaShanah* - The letter N, D, or P denotes the year length:
- N = "Normal" year:
*Cheshvan*has 29 days but*Kislev*has 30 days (full cycle frequency^{203785}/_{689472}≈ 29.6% of years) - D = "Deficient" year: both have 29 days (full cycle frequency
^{58633}/_{229824}≈ 25.5% of years) - P = "Perfect" (also called "Abundant") year: both have 30 days (full cycle frequency
^{77447}/_{172368}≈ 44.9% of years)

- N = "Normal" year:
- A digit 1, 3, 5, or 7 denotes the first weekday of Passover
- An asterisk denotes a leap year, in which the 30-day month
*Adar Rishon*is inserted before the 29-day*Adar*(renamed to*Adar Sheini*).

The 4-digit Hebrew year number to the left of each "=" sign is an example of the year type that is to the right of the "=" sign, and the small number (in parentheses) was the first year of that type after the Hebrew calendar epoch. Below that is the total count of that year type and its exact frequency and approximate percentage in the full calendar cycle. The omitted weekdays (1, 4, 6) are disallowed as the first day of *Rosh HaShanah*. Blank cells are length and weekday combinations that never occur. Hebrew calendar days begin at local sunset. After civil midnight the corresponding English weekday names are: 1 = Sunday, 2 = Monday, ... 7 = Saturday.

Start Rosh onHaShanah |
435456 = ^{12}/_{19} ≈ 63.2% Common Years (Non-Leap) |
254016 = ^{7}/_{19} ≈ 36.8% Leap Years |
Totals by Weekday |
||||
---|---|---|---|---|---|---|---|

Deficient 353 days = 50+ ^{3}/_{7} weeks |
Normal 354 days = 50+ ^{4}/_{7} weeks |
Perfect 355 days = 50+ ^{5}/_{7} weeks |
Deficient 383 days = 54+ ^{5}/_{7} weeks |
Normal 384 days = 54+ ^{6}/_{7} weeks |
Perfect 385 days = 55 weeks |
||

2 = Yom Sheini |
5773 (15) = 2D3 39369 = ^{13123}/_{229824}≈ 5.7% |
5780 (1) = 2P5 81335 = ^{81335}/_{689472}≈ 11.8% |
5793 (8) = 2D5* 40000 = ^{625}/_{10773}≈ 5.8% |
5779 (14) = 2P7* 32576 = ^{509}/_{10773}≈ 4.7% |
193280 = ^{3020}/_{10773}≈ 28.0% |
||

3 = Yom Shlishi |
5786 (4) = 3N5 43081 = ^{43081}/_{689472}≈ 6.2% |
5782 (27) = 3N7* 36288 = ^{1}/_{19}≈ 5.3% |
79369 = ^{79369}/_{689472}≈ 11.5% |
||||

5 = Yom Chamishi |
5772 (7) = 5N7 124416 = ^{24}/_{133}≈ 18.0% |
5832 (23) = 5P1 22839 = ^{7613}/_{229824}≈ 3.3% |
5812 (3) = 5D1* 26677 = ^{3811}/_{98496}≈ 3.9% |
5771 (6) = 5P3* 45899 = ^{6557}/_{98496}≈ 6.7% |
219831 = ^{73277}/_{229824}≈ 31.9% |
||

7 = Yom Shabbat |
5781 (26) = 7D1 29853 = ^{3317}/_{76608}≈ 4.3% |
5791 (2) = 7P3 94563 = ^{79}/_{576}≈ 13.7% |
5801 (19) = 7D3* 40000 = ^{625}/_{10773}≈ 5.8% |
5858 (25) = 7P5* 32576 = ^{509}/_{10773}≈ 4.7% |
196992 = ^{2}/_{7}≈ 28.6% |
||

Totals by Year Length |
69222 = ^{11537}/_{114912}≈ 10.0% |
167497 = ^{167497}/_{689472}≈ 24.3% |
198737 = ^{28391}/_{98496}≈ 28.8% |
106677 = ^{1317}/_{8512}≈ 15.5% |
36288 = ^{1}/_{19}≈ 5.3% |
111051 = ^{1371}/_{8512}≈ 16.1% |
689472 = 100% |

The following table summarizes the number of *Torah* portions that are combined in Israel and in the diaspora for each of the 14 calendar year types. All year types in which Passover starts on *Yom Chamishi* or on *Shabbat* have one more combined *Torah* portion in the diaspora than in Israel. Only deficient leap years in which Passover starts on *Yom Rishon* have zero combined portions in both Israel and the diaspora. Leap years in which Passover starts on *Shabbat* have zero combined portions in Israel, but one combined portion in the diaspora. Seven is the maximum possible number of combined portions, occurring only in the diaspora in common years in which Passover starts on *Yom Chamishi*. In Israel six is the maximum possible number of combined portions, occurring in common years in which Passover starts on *Yom Shlishi* or on *Yom Chamishi*.

Start Passover(15 Nisan) on |
Year Length | Common Years (Non-Leap) | Leap Years | ||||
---|---|---|---|---|---|---|---|

Example = Character | Combined in Israel | Combined in Diaspora | Example = Character | Combined in Israel | Combined in Diaspora | ||

1 = Yom Rishon |
Deficient | 5781 (26) = 7D1 | 5 | 5 | 5812 (3) = 5D1* | 0 | 0 |

Perfect | 5832 (23) = 5P1 | 4 | 4 | ||||

3 = Yom Shlishi |
Deficient | 5773 (15) = 2D3 | 6 | 6 | 5801 (19) = 7D3* | 2 | 2 |

Perfect | 5791 (2) = 7P3 | 6 | 6 | 5771 (6) = 5P3* | 1 | 1 | |

5 = Yom Chamishi |
Deficient | 5793 (8) = 2D5* | 2 | 3 | |||

Normal | 5786 (4) = 3N5 | 6 | 7 | ||||

Perfect | 5780 (1) = 2P5 | 6 | 7 | 5858 (25) = 7P5* | 2 | 3 | |

7 = Yom Shabbat |
Normal | 5772 (7) = 5N7 | 4 | 5 | 5782 (27) = 3N7* | 0 | 1 |

Perfect | 5779 (14) = 2P7* | 0 | 1 |

Those who observe only single High Holy Days yet live outside Israel can use the algorithm described herein either by modifying it to always use the rules for Israel, or by defining all locales as if they are inside Israel. This algorithm doesn't support the triennial *Torah* portion cycles that are followed by many Reform and some Conservative congregations, because the variants that they follow are too divergent to accommodate, and in recent history their rules have been subject to inconsistent changes.

I have specifically avoided using a direct "brute force" table lookup strategy (based on tables listing all *parshiot* for all Saturdays of all 14 year types of the traditional Hebrew calendar, including separate tables for the diaspora and for Israel), as is commonly found in printed works and probably many computer programs, even though such an algorithm would execute faster, because that approach is incompatible with calendar variants that allow any month to have 29 or 30 days, and because compiling all of the necessary lookup tables is a tedious and error-prone task. On the other hand, one who implements a computer program based on the algorithm and rules given herein will be able to automatically generate such tables (see also the heading "Verification" at the end of this web page), which might be useful for publishing error-free manual lookup charts.

Even though the algorithm allows some flexibility with regard to the underlying calendar structure, its logic nevertheless depends on the presence of the full standard set of High Holy Days throughout the year, otherwise it will run out of *Torah* portions near the end of the year! Computer programs that suppress High Holy Days in the remote past, for example for dates prior to the Revelation at Sinai, should avoid using this algorithm for such dates. In fact, there is little point in quoting a *Torah* portion for any date prior to the era of the Maccabees, who, after rededicating the Second Temple and declaring the festival of *Chanukah* in Hebrew year 3623, established the regular public *Torah* reading tradition that continues today. We don't know, however, how the *Torah* portions were adapted to the unpredictable observational Hebrew calendar, which allowed any month to have 29 or 30 days, depending on when the first new lunar crescent was seen, which was in use until the traditional fixed arithmetic traditional calendar was established in Hebrew year 4119.

In the second-last section of this page I will also give brief rules for determining if a *Shabbat* is special, that is not a festival or High Holy Day but having a special *Haftorah* reading rather than the one that belongs with the regular weekly *Torah* portion, or having some other ritual significance.

There are a certain number of Saturdays in the Hebrew year, depending on the starting weekday (*Rosh HaShanah* can only start on Monday, Tuesday, Thursday, or Saturday) and the length of the year (non-leap *vs.* leap; deficient, regular, or full), yielding a total of 14 possible year types. The list of *Torah* portions are to be sequentially read, starting with *Bereishit* on the *Shabbat* after *Simchat Torah* and continuing through and ending up at *Haazinu* on the last regular *Shabbat* before the *Succot* of the following Hebrew year. During that sequence certain *Torah* portions are combined into double portions, depending on the length of the year, the number of Saturdays "missed" from the regular sequence because of a festival or High Holy Day, and whether the locale is in the diaspora or in Israel.

The enumerated list of *Torah* portions follow. Note that the last portion, *V'zot HaBrachah*, is read on *Simchat Torah* and is never read during the morning service on a regular *Shabbat*, although its first *aliyah* is read during the *Minchah* service on *Shabbat Haazinu* and may be read on a Monday or Thursday morning prior to *Succot* (when a Monday or Thursday exists between *Shabbat Haazinu* and *Succot*).

1) | Bereishit |
10) | Mikeitz |
19) | Terumah |
28) | Metzora |
37) | Shelach |
46) | Eikev |

2) | Noach |
11) | Vayigash |
20) | Titzaveh |
29) | Acharei Mot |
38) | Korach |
47) | Re'eh |

3) | Lech Lecha |
12) | Vayechi |
21) | Ki Tisa |
30) | Kedoshim |
39) | Chukat |
48) | Shoftim |

4) | Vayeira |
13) | Shemot |
22) | Vayakhel |
31) | Emor |
40) | Balak |
49) | Ki Teitzei |

5) | Chayei Sarah |
14) | Va'eira |
23) | Pekudei |
32) | Behar |
41) | Pinchas |
50) | Ki Tavo |

6) | Toldot |
15) | Bo |
24) | Vayikra |
33) | Bechukotai |
42) | Mattot |
51) | Nitzavim |

7) | Vayeitzei |
16) | Beshalach |
25) | Tzav |
34) | Bamidbar |
43) | Masei |
52) | Vayeilech |

8) | Vayishlach |
17) | Yitro |
26) | Shemini |
35) | Nasso |
44) | Devarim |
53) | Haazinu |

9) | Vayeishev |
18) | Mishpatim |
27) | Tazria |
36) | Beha'alotcha |
45) | Ve'etchanan |
54) | V'zot HaBrachah |

The given date can be any weekday and can be a normal day, a festival, a High Holy Day, or a day of public fasting. If the given date is a regular weekday then the *Torah* portion to return is that of the next regular *Shabbat*.

This algorithm assumes that the given date has already been checked to determine if it is a festival or High Holy Day, and that information is available. It also assumes that the ordinal day numbers of all required dates are known relative to any convenient epoch, so that simple arithmetic operations can be carried out directly, such as adding or subtracting any integer number of days, or dividing an interval by 7 to determine the number of weeks that it contains.

The following are the only *Torah* portions that are ever combined:

*Vayakhel - Pekudei*(earliest possible, always 22 weeks after*Simchat Torah*)*Tazria - Metzora**Acharei Mot - Kedoshim**Behar - Bechukotai**Chukat - Balak*(never in Israel)*Mattot - Masei**Nitzavim - Vayeilech*

On *Shabbat*, if the given date is a festival or High Holy Day (*yom tov*) or an intermediate festival day (*chol ha-moed*) then the weekly *Torah* portion is delayed and a special reading for that event is read instead.

On Monday and Thursday morning, if the given date is a *yom tov* or *chol ha-moed*, the last day of a 30-day month or the first day of any month (*Rosh Chodesh*), *Hoshanah Rabbah*, *Purim*, any day of *Chanukah*, or any public fasting day then the appropriate *Torah* portion is the special reading for that event instead of the regular weekly *parshah*.

In a computer program that supports calculations involving remote past dates, suppress all *Torah* portions prior to Hebrew year 3623, which was the year when the festival of *Chanukah* was declared by the Maccabees.

Otherwise we continue with the algorithm (names of variables are shown in *italics*):

Preset *TargetShabbat* to equal the given date.

If the given date is not *Shabbat* then search for the next regular *Shabbat* and set that date as the *TargetShabbat*.

Find the nearest *Simchat Torah* prior to the *TargetShabbat*. Outside Israel that is the 23rd of *Tishrei*, in Israel that is the 22nd of *Tishrei*.

Preset *WorkingShabbat* equal to the *Shabbat* after *Simchat Torah*, less 7 days.

Calculate the simple number of Saturdays that exist from *Simchat Torah* to *TargetShabbat*:

*ParshahNumber* = ( *TargetShabbat* – *WorkingShabbat* ) / 7.

If *PashahNumber* < 22 THEN this is one of the first 21 *parshiot* that occur prior to *Vayakhel* and are never combined. Simply return the corresponding *parshah* name from the list above. Otherwise continue with the algorithm.

Set *ParshahNumber* = 21 and add 147 to *WorkingShabbat* (147=21×7).

Henceforth we will iteratively check through the portions until we get to the *TargetShabbat*, incrementing the *ParshahNumber* as we go.

At this point we need the following additional information:

Is the

TargetShabbatin a non-leap year, or in a leap year?Find the first day of

Passover, on the 15th ofNisan, and determine its weekday.

Add 7 days to *WorkingShabbat*. If that *Shabbat* is *yom tov* or *chol ha-moed* then skip it.

Having found the next regular *Shabbat*, increment the *ParshahNumber*.

At the beginning of each iteration through the loop, default to not combining the portions for this week by setting *Combined* = FALSE. As we go through the algorithm, if the rules indicate that the portion is combined with the next then have the logic remember that by setting *Combined* = TRUE. At the end of each iteration through the loop, if *Combined* = TRUE then increment *ParshahNumber* to take into account that combined portion.

The only *ParshahNumber* values that require special checking are numbers 22, 27, 29, 32, 39, 42, and 51:

## Case 22:

Vayakhel(combine withPekudei?)Check how many Saturdays exist from

WorkingShabbatuntil the day beforePassover. If there are less than 4 then combineVayakhelwithPekudei(there are only 3 Saturdays left beforePassoverin years in which these portions are combined).Note that the algorithm goes only to the day before

Passoverso as not to includePassoverin the count whenPassoverlands on Saturday, becausePassoveritself is ayom tovwith its own specialTorahportion. TheWorkingShabbatis included in the count because it has to be a regularShabbat.## Case 27:

Tazria(combine withMetzora?)Combine if NOT a leap year.

## Case 29:

Acharei Mot(combine withKedoshim?)Combine if NOT a leap year.

## Case 32:

Behar(combine withBechukotai?)Outside Israel: Combine if NOT a leap year.

Inside Israel: Combine if

Passoverdoes not start onShabbatAND NOT a leap year.

ThePassoverexception only occurs in a 354-day year in whichRosh HaShanahstarts on Thursday.## Case 39:

Chukat(combine withBalak?)Outside Israel: Combine if

Passoverstarts on Thursday (because in such a case the second day ofShavuotfalls onShabbatin the diaspora).Inside Israel: Never combine.

## Case 42:

Mattot(combine withMasei?)Combine if there are less than 3 Saturdays from

WorkingShabbattoTisha B'Av(9th day of the month ofAv), so thatDevarimis the portion that will be read on theShabbatbeforeTisha B'Av.## Case 51:

Nitzavim(combine withVayeilech?)This is always the last

ShabbatinElul. The classical rule is to combine these portions if there is only oneShabbatbetween the comingRosh HaShanahandSuccot, but equivalently in terms of calendrical arithmetic it is simpler to combine if eitherRosh HaShanahorYom Kippurwill land onShabbat. The following novel rule is even simpler and works with all possible years types of the traditional or rectified Hebrew calendars:Determine the number of days until the coming

Rosh HaShanah, then combine if >3 days.

If, from the above exceptions, the *WorkingShabbat* has combined portions then increment *ParshahNumber*.

**Continue looping for one week at a time until WorkingShabbat reaches the TargetShabbat.**

For the case of a given date that is after *Shabbat Haazinu* and is a Monday or Thursday before *Succot* the above logic returns *ParshahNumber* = 1, but that does not apply until after *Simchat Torah*. Therefore if *ParshahNumber* = 1 AND the given date is before the 15th of *Tishrei* (the first day of *Succot*) then change the *ParshahNumber* = 54 to return *V'zot HaBrachah* instead.

Finally, return the name of the *parshah* as follows: If the *TargetShabbat* was found to have combined portions then the *ParshahNumber* was already incremented so from the list of *Torah* portion names return the name at *ParshahNumber* – 1, append a dash (or whatever separator is desired), and also return the name at *ParshahNumber*, otherwise it is a single portion so just return the name at *ParshahNumber* from the list.

See also Jerrold Landau’s discussion of special days, here: https://jerroldlandau.com/Special_Days_(12).php.

*Shabbat Mivarchim* is the last *Shabbat* before *Rosh Chodesh*, whereupon the congregation recites a special blessing for the coming month, and the *molad* moment is announced, before commencing the *Shabbat Musaf* service.

*Shabbat Machar Chodesh* is the occasional Saturday which falls on the 29th day of a month other than *Elul* (in the traditional and rectified Hebrew calendars 29 *Elul* can never land on *Shabbat*), which is the day before *Rosh Chodesh*. If that *Shabbat* is special for any other reason listed below then that usually overrides its status as *Shabbat Machar Chodesh*, although there are some opinions that in such cases the first and last sentence of the *Machar Chodesh Haftorah* should be read after the *Rosh Chodesh Haftorah*.

*Shabbat Rosh Chodesh* is the occasional Saturday which falls on *Rosh Chodesh* (the first or 30th day of the month).

Don't confuse this event with *Shabbat HaChodesh*!

**How often does Shabbat Rosh Chodesh occur?** For a detailed single-page analysis, click here: (Note that dates marked as "Never" are due to interactions with the

*Shabbat Shuvah*, also known as *Shabbat Teshuvah*, is the Saturday between *Rosh HaShanah* and *Yom Kippur* (day in *Tishrei* = 3rd to 9th, although the 9th is impossible if *Rosh HaShanah* can never start on Friday). On this day the congregation or *yeshiva* rabbi usually delivers a major *derashah* (longer than usual sermon), typically on the topic of repentence, during either the morning services or prior to the afternoon service. In addition to its ritual significance, at 2 am the following night Israel switches from Daylight Saving Time to Standard Time.

As of March 15th, 2005 (Gregorian) the law in Israel for Daylight Saving Time is: "Every year, from the last Friday before April 2nd at 02:00h until the last Sunday before the 10th of Tishrei at 02:00h, the time in Israel shall be advanced by one hour, thus leading Coordinated Universal Time by 3 hours."

Source: This law has appeared in Hebrew on the web site of the Israeli Government Ministry of the Interior, but the URL has been changed multiple times.

*Shabbat Shirah* is that *Shabbat* upon which the *Torah* portion *Beshalach* is read, 16 weeks after *Simchat Torah*. That *Torah* portion contains the song that the Children of Israel sang after safely crossing the Red Sea.

*Shabbat Chanukah* is a *Shabbat* falling within the festival of *Chanukah*, from the 25th of *Kislev* to the 2nd of *Tevet*, inclusive. If the 30th of *Kislev* is a Saturday then it is both *Shabbat Chanukah* and *Shabbat Rosh Chodesh*, it being both the 6th day of *Chanukah* and the first day of *Rosh Chodesh*.

On the Traditional and Rectified Hebrew calendars the 5th day of

Chanukah(on the 29th day ofKislev) is neverShabbat, and the 6th day can only beShabbat Rosh ChodeshwhenKislevhas 30 days (because the first day ofTevetis neverShabbat). When the first day ofChanukah(on the 25th ofKislev) isShabbat Chanukahthe eighth day ofChanukah(on the 2nd day ofTevet) is alsoShabbat Chanukah, but this is only possible whenRosh HaShanahstarts onShabbatand the year is "perfect", with 30 days in bothCheshvanandKislev.

*Shabbat Shekalim* is first day of *Adar* in non-leap years or *Adar Sheini* in leap years if that is a Saturday, otherwise it is the prior *Shabbat* (in the last 6 days of the prior month). When it lands on the first day of *Adar* in non-leap years or *Adar Sheini* in leap years it coincides with the second day of *Rosh Chodesh*. If can never land on the first day of *Rosh Chodesh* (the last day of *Shevat* in non-leap years or the last day of *Adar Rishon* in leap years), however, because in the traditional and rectified Hebrew calendar those days can never be *Shabbat*.

*Shabbat Zachor* is the *Shabbat* before *Purim* (day in last month of year = 8th to 13th).

Jerusalem only: If the 15th day of the last month of the year lands on *Shabbat*, then it is *Shabbat Shushan Purim*.

*Shabbat Parah* is the Saturday before *Shabbat HaChodesh* (days remaining before *Nisan* = 7th to 13th).

*Shabbat HaChodesh* is the first day of *Nisan* if that is a Saturday (in which case it coincides with *Rosh Chodesh*), otherwise the prior *Shabbat* (days remaining before *Nisan* = 0 to 6).

*Shabbat HaGadol* is the last *Shabbat* before *Passover* (day in *Nisan* = 8th to 14th). On this day the congregation or *yeshiva* rabbi usually delivers a major *derashah* (longer than usual sermon), typically on a topic related to the exodus from Egypt and/or *Passover* preparations, during either the morning services or prior to the afternoon service. When *Shabbat HaGadol* will be the day before *Passover* starts, however, some rabbis advance this *derashah* one week earlier so that it will be more relevant.

*Shabbat Chazon* (Prophesy) is the *Shabbat* before *Tisha B'Av* (day in *Av* = 4th to 9th). When the 9th of *Av* is *Shabbat*, observation of *Tisha B'Av* is postponed to the 10th of *Av*, hence this special *Shabbat* sometimes lands on the 9th.

*Shabbat Nachamu* (Consolation) is the *Shabbat* after *Tisha B'Av* (day in *Av* = 10th to 16th).

One who implements the rules documented herein ought to verify correct operation before relying on it. There are of course traditional sources that one may compare with. The reader can also compare with the "Events" window and Hebrew Calendar *Zmanim* export reports of my Windows freeware calendar calculator, *Kalendis* (in HTML, Tab-Delimited Text, or Comma-Separated Value formats), which follows the above rules as of version 9.259(981).

In addition, I generated full listings for all 14 calendar year types of the Traditional Hebrew Calendar for both Israel and the diaspora, which you can download in Microsoft Excel format by clicking here:

Torah-Portions.xls 228KB

See the "Explain" worksheet in the file. The spreadsheet requires Microsoft Excel or a compatible program such as LibreOffice Calc or OpenOffice Calc.

If you wish to know which dates a certain *Torah* portion or special *Shabbat* can fall on (limited by there being only 14 possible types of Hebrew calendar year) then you easily view that information in the spreadsheet by using its built-in autofilter menus. Similarly you can easily view which types of year have particular portions combined.

Updated 29 *Nisan* 5781 (Traditional) = 29 *Nisan* 5781 (Rectified) = Apr 14, 2021 (Symmetry454) = Apr 14, 2021 (Symmetry010) = Apr 11, 2021 (Gregorian)