On Monday and Thursday, we say a longer Tachanun. On a fast day (where the weekday prayers are still said), Selichot are said in addition to Tachanun.

It feels like there are many more fasts that fall out on Monday and Thursday. Is this statistically true, or does it just feel that way because I always remember having to say the longer Tachanun in addition to the Selichot? (availability bias)


3 Answers 3


Considering Monica's point about year distributions, here's a refinement of Gershon's data (using the frequency table on Remy Landau's Hebrew Calendar page, here):

  • Tzom Gedaliah falls on Monday or Thursday in the year types גכה, זחא, זשג, גכז, זחג, זשה. This is 40.08% of all years.

  • Asarah B'Teves can't occur on Monday, but it can be on Thursday, only in the year type הכז. This happens to be the single most common keviah, occurring in 18.05% of all years.

  • Taanis Esther can be on Monday or Thursday quite often (largely because of the cases where it is moved up from Shabbos) - indeed, the only time it's not is when Purim itself is on Thursday, which is in the year types הכז, בשז, גכז. The fast is therefore on Monday or Thursday 71.97% of the time.

  • Shiva Asar B'Tammuz can't fall on Monday, but it can be on Thursday, in the year types בשה, גכה, בחה, זשה. These are 28.57% of all years.

  • Same thing for Tisha B'Av: it's on Thursday in 28.57% of all years.

So the only one that occurs on Monday or Thursday a majority of the time is Taanis Esther, with Tzom Gedaliah being a distant second.

All told, if you consider the full Hebrew calendar cycle of 689472 years, with five fasts in each one, then you'll have that a fast occurs on Monday or Thursday 37.45% of the time.

  • How does removing Tisha B'av affect the total percentage (since Tisha B'av is not a fast where we say Selichot)?
    – Menachem
    Jan 5, 2012 at 18:08
  • 6
    ...which means that the asker's suspicion is correct: fasts do occur more often on Monday and Thursday than on other days. That is, they occur on Monday and Thursday (33% of the days) 37% of the time. +1.
    – msh210
    Jan 5, 2012 at 18:09
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    @Menachem, 39.67% discounting 9 Av assuming the numbers in this answer are correct.
    – msh210
    Jan 5, 2012 at 18:11
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    @msh210, interesting (your first comment) - that didn't even occur to me! I was looking just at the raw percentages and thinking to myself that 37% is far from a majority. (Hm, maybe we need a slogan: "33% of the weekdays have 37% of the fast days. Occupy BaHaB!" :)
    – Alex
    Jan 5, 2012 at 18:24
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    @DanielbenNoach: fasts (except for Yom Kippur) can't occur on Shabbos, so that leaves six weekdays to work with; Monday and Thursday are indeed 33% of those.
    – Alex
    Jan 6, 2012 at 1:07

I used the data from hebcal.com/hebcal and the linux command line to see how many times the various fasts actually fell on Monday or Thursday.

  • First, I downloaded the Event Lists for the years 5514 through 5572. I started from 5514 because, according to the website, results for year 1752 C.E. and before may not be accurate. "Hebcal does not take into account a correction of ten days that was introduced by Pope Gregory XIII known as the Gregorian Reformation."

    This is 229 years of data.

    for i in `seq 5514 5772`; do 
     wget -c "http://www.hebcal.com/hebcal/?year=${i};month=x;yt=H;v=1;nh=on;nx=on;mf=on;ss=on;i=off;lg=s;c=off;geo=zip" -O $i
  • Then I searched for the number of instances the fasts fell on Monday or Thursday

     for i in Gedalia Asara Esther "Tzom Tammuz" ;do 
          COUNT=`cat 5* |grep "$i" |egrep "Mon|Thu" |wc -l`
          TOTAL=`ls 5* |wc -l`
          echo -e "$i\t\t== $COUNT / $TOTAL == `echo "scale=4; $COUNT/$TOTAL"|bc`"
  • This gave me the following results:

      Gedalia   == 93 / 229 == .4061
      Asara     == 41 / 229 == .1790
      Esther    == 166 / 229 == .7248
      Tzom Tammuz   == 65 / 229 == .2838

These are almost exactly the same numbers that Alex got.

And this code:

for i in Gedalia Asara Esther "Tzom Tammuz" ;do 
    for j in Sun Mon Tue Wed Thu Fri Sat
        DAY_COUNT=`cat 5* |grep "$i" |grep "$j" |wc -l`
        echo -e "${i}:\t${j}\t==\t$DAY_COUNT"
    echo "----------------------------------------------"

gave me the break down for each of the fasts by days of the week:

Gedalia:    Sun ==  74
Gedalia:    Mon ==  66
Gedalia:    Tue ==  0
Gedalia:    Wed ==  62
Gedalia:    Thu ==  27
Gedalia:    Fri ==  0
Gedalia:    Sat ==  0
Asara:  Sun ==  68
Asara:  Mon ==  0
Asara:  Tue ==  64
Asara:  Wed ==  10
Asara:  Thu ==  41
Asara:  Fri ==  46
Asara:  Sat ==  0
Esther: Sun ==  0
Esther: Mon ==  65
Esther: Tue ==  0
Esther: Wed ==  63
Esther: Thu ==  101
Esther: Fri ==  0
Esther: Sat ==  0
Tzom Tammuz:    Sun ==  90
Tzom Tammuz:    Mon ==  0
Tzom Tammuz:    Tue ==  74
Tzom Tammuz:    Wed ==  0
Tzom Tammuz:    Thu ==  65
Tzom Tammuz:    Fri ==  0
Tzom Tammuz:    Sat ==  0
  • Technically Hebcal’s disclaimer regarding the Gregorian calendar is inaccurate. The calendar has existed since 1583; it just wasn’t adopted by most of the world until 1752 (and even after then, some countries were still holdouts). That said, this restriction (either date) should bear no influence on the question at hand, as the change of calendar didn’t affect the day of the week, just the day of the month.
    – DonielF
    Mar 28, 2019 at 3:00

No! It just feels that way. - Analyzing from 5761-5772 35 times not on Monday or Thursday and 25 times on a Monday or Thursday.

Tisha B'Av & Shiva Asar B'Tamuz can only come out on either Sunday, Tuesday, Thursday, or Shabbos and then it is observed on Sunday - so for these two fasts it is impossible to fall out on Monday and more likely to fall out on another day of the week.

Tzom Gedalya can only come out on Monday, Wednesday, Thursday, or Shabbos and then it is observed on Sunday - so it has a 50/50 chance of falling out on Monday or Thursday. (analyzing 5761-5790 - 30 year period - 16 times not on Monday or Thursday / 14 times on a Monday or Thursday)

Taanis Esther can only come out on Monday, Wednesday, Thursday, or Shabbos and then it is observed on Thursday - so there is a 75% chance of falling out on Monday or Thursday.

Asara B'Teveis can only fall out on Sunday, Tuesday, Wednesday, Thursday or Friday - so there is no chance of it happening on a Monday and only a 20% chance of it falling on a Thursday. (analyzing 5761-5790 - 30 year period - 26 times not on Monday or Thursday / 4 times on a Thursday)

  • 3
    Good analysis. One thing missing, though, is the year-to-year distribution. For example, Tzom Gedalya can only fall on four days, but does it fall on each of them 25% of the time or is it more unbalanced? Jan 5, 2012 at 17:23
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    It does seem from those odds that it might be more likely to fall out on Thursday than Monday, at least.
    – Seth J
    Jan 5, 2012 at 17:26
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    I agree with @MonicaCellio that the days of the week a fast can occur on does not at all imply how often it will occur on them. The actual prevalence is telling, but would be more so if taken over a complete 247-year cycle, which I guess is what Alex's answer did.
    – msh210
    Jan 5, 2012 at 18:07

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