This Halacha is an excerpt from our Sefer
It is forbidden to eat or drink anything on Tisha B’av.
A. People who are sick; Women who are pregnant, nursing, or after birth:
One who is sick: A person who is sick and needs to eat, is not required to fast on Tisha B’av. If he needs to eat he is required to break his fast. [Anyone who feels weak and sick to the point he is bedridden, is considered sick in this regard, even if it is not life threatening.]
Pregnant woman: A pregnant woman must fast on Tisha B’av just like on Yom Kippur. [If, however, a pregnant or nursing woman feels weak and will become sick due to the fast, she is not to fast. If a pregnant woman begins to feel dizzy or begins to experience labor [i.e. contractions] or low/high blood pressure, she is to break her fast. Certainly, if she feels sick and needs to lay in bed, she is to break her fast. Some Poskim are lenient for all pregnant women who are prior to their due date, to not fast if it is very difficult due to the hot weather. Furthermore, some Poskim are lenient in all cases that a pregnant woman prior to her due date is not to fast, due to fear of miscarriage. Practically, such a woman is to contact a Rav for a final ruling.]
Nursing woman: A nursing woman must fast on Tisha B’av just like on Yom Kippur. [However, a nursing woman who feels sick and needs to lay in bed, is not to fast. If a nursing mother feels healthy, but she will not have milk for her child if she fasts, then if her child only eats from her, she may break her fast. Some Poskim rule that even if she is able to feed the child formula and the like, nevertheless, she is not required to do so. Practically, such a woman is to contact a Rav for a final ruling.]
A woman who is after childbirth: A woman within 30 days of childbirth is not required to fast. Nevertheless, the custom is to fast unless she is experiencing great pain, in which case there is worry of danger. Nonetheless, a woman may choose to be lenient against this custom and not fast within thirty days of birth even if she is not in pain. [Practically, in today’s times all women within thirty days of birth are to be taught not to fast. However some Poskim rule that a woman who is after seven days, and feels healthy, is to fast. Accordingly, such a woman is to contact a Rav for a final ruling. Certainly, if she is within seven days of birth, and even more so if she is within three days of birth, it is forbidden for her to fast.]
Taanis Nidche: If the fast fell on Shabbos and was hence differed to Sunday, one may be lenient not to fast even if he or she is a slightly sick, and is not bedridden. [Thus, a pregnant woman may break her fast if she feels too weak or slightly sick.]
If a pregnant woman began to have contractions, is she to break her fast?
From beginning of pregnancy up to 9th month: If a pregnant woman who is not yet in her 9th month feels contractions that can lead to miscarriage or early birth, or if she feels pressure to push out the baby, then she is to eat and drink any amount of food until her body calms down.
After 9th month: A pregnant woman who has completed her 9th month [past week 37 from conception] is not to break her fast unless she has entered into active labor to the point she cannot walk, is on the birthing stool, or has broken her waters, just as is the law regarding transgressing Shabbos. When she reaches this point, she may eat regularly. However, prior to reaching this state, she is not to eat or drink, unless she feels sick or bedridden.
When exempt from fasting, as stated above, must one nevertheless try to fast as many hours as possible?
Some Poskim rule that one who is exempt from fasting should at the very least fast for a few hours, if it is not too difficult. Practically, the final Rabbinic directive is that one who is exempt from fasting may eat immediately in the morning. Nevertheless, if possible, one is try to fast at night, until the morning. When Tisha B’av falls on Motzei Shabbos, if one is able to fast until the morning, Havdala is not to be recited until the next day.
Must one who needs to eat or drink only take the minimal measurements “Shiurim” as required on Yom Kippur?
Some Poskim rule one is required to follow the same eating and drinking measurements “Shiurim” prescribed on Yom Kippur. Other Poskim however rule it is not necessary. Practically, the custom is not to follow the former opinion, and hence one who is permitted to eat or drink may do so without limitation.
If one is medically required to drink, must he nevertheless abstain from eating foods?
Yes. He is to refrain from eating, but may drink, as is medically required.
If one is medically required to eat only at night, is he to fast by the daytime of Tisha B’av?
May one who is not required to fast eat like a normal day?
It is proper to diminish somewhat in eating and drinking if one is not fasting that day, in order to participate in the day of oppression followed by the community.
May one take medicine on a fast day?
If one is sick then he is not required to fast, as explained above. Even if one is not sick, it is permitted to take medicine, if the medicine is bitter. He is to swallow it without water or alternatively place something bitter in the water and use this water to help swallow the pill. [If one is unable to do so, then the medicine may be taken with regular water if the person will fall sick if he does not take it.]
When Tisha B’av falls on Sunday, must one who is not fasting say Havdala prior to eating?
Yes. This includes men and women.
What is the Seder of Havdala in such a case? One omits the verses of “Hinei Keil Yeshuasi”, and rather begins from the blessing of Hagafen or Shehakol [depending on his beverage]. The blessing of Besamim is omitted. If this Havdala is being recited on Sunday, the blessing of Haeish is likewise omitted, and is to be said the night before.
Is wine to be used or Chamer Medina? Some Poskim rule one is to use wine or grape juice. Others rule one is only to use Chamer Medina, such as tea or coffee. If there is a child available who has not reached the age of Chinuch for mourning but is past the age of Chinuch for blessings, one may say Havdala over wine and give him to drink.
B. Children Fasting:
All children who are above the age of Bar or Bas Mitzvah are obligated to fast on all accustomed fast days. All children who are below the age of Bar or Bas Mitzvah, are not required to fast any of the four Rabbinical fasts, including Tisha B’av. [This applies even if the child is within three fasts from his/her Bar/Bas Mitzvah. One is not even required to educate the child to fast for a certain amount of hours into the day [i.e. Taanis Shaos]. Nevertheless, some Poskim rule that regarding Tisha B’av, children who have reached the age of education in this regard, which is approximately nine years old, are to delay their meals a few hours into the day from its set time. However, children below the age of education are to be fed like normal and it is even forbidden to delay their meals from their regular times, being that this can lead them to becoming in a state of danger.]
What may the children eat? Some Poskim rule that a child who has reached the age of understanding the mourning is only to be allowed to eat bread and water or other simple staple food. The custom however is not like this opinion. [However, they are not to be given sweets and the like, although one is not required to stop them from eating it if they are in the midst of doing so.]
Are children to fast on the night of Tisha B’av until morning?
The custom of many is that children of Chinuch age fast until the morning. This is not required from the letter of the law.
If one is not fasting, is he to wash hands as usual [until the wrist] when eating bread on Tisha B’av?
If a child below Bar/Bas Mitzvah desires to fast on Tisha B’av, may the parent allow him to do so?
If the child is already close to the age of Bar/Bas Mitzvah and the parent does not see any danger involved for the child to fast, then although he may not force the child to fast, he is also not required to protest him from fasting.
When Tisha B’av falls on Sunday, are children who have reached the age of Chinuch to say Havdala prior to eating?
If a child became Bar Mitzvah on Sunday Tisha B’av Nidche, must he fast?
C. Does one who eats bread on Tisha B’av recite Nachem in Birchas Hamazon?
One who eats bread on Tisha B’av is to say Nachem in Birchas Hamazon. It is recited prior to Uvinei Yerushalayim. It is recited each time that one recites Birchas Hamazon on Tisha B’av. [However, some Poskim rule that based on Admur in the Siddur one is not to recite Nacheim in Birchas Hamazon. Practically it is to be recited. Children who ate bread are to recite Nachem in Birchas Hamazon.]
If one is not fasting, is he to wash hands as usual [until the wrist] when eating bread on Tisha B’av?
 Michaber 554:6
 The reason: As the Sages did not institute the fast for those who are sick [Michaber ibid]
 “He is to be fed immediately” [Michaber ibid]
 See M”B 554:11
 Michaber 554:5; Rama 550:1; Pesachim 54b
 Aruch Hashulchan 554:7; Piskeiy Teshuvos 554:5
The reason: As she is considered like a sick person. [ibid]
 See Q&A!
 Piskeiy Teshuvos ibid; and so I received from Harav Asher Lemel Hakohen
 Rav SZ”A in Halichos Beisa 25:2; Tzedaka Umishpat Hakdama; Rav Yaakov Yosef; See Nitei Gavriel 65 footnote 2
 Rav Yaakov Yisrael Fisher [brought in Sefer Pnei Baruch; Piskeiy Teshuvos 617 footnote 1] was of the opinion that today pregnant women no longer have to fast, and may eat less than the Shiur on Yom Kippur, due to danger of miscarriage. Practically, this ruling is not accepted amongst Poskim or Moreh Horaas and rather each case must be judged individually by a competent Rav. [Tzitz Eliezer 17:20; Teshuvos Vehanhagos 2:292; Piskeiy Teshuvos 617:1; Rav Ovadia Yosef] However, Rav Yaakov Yosef ruled after a thorough investigation amongst doctors, and discovering a dispute amongst them as to the dangers of fasting, regarding Tisha B’av which is a Rabbincial fast, one may be lenient.
 Michaber 554:5; Rama 550:1; Pesachim 54b
 Piskeiy Teshuvos 554:6
 See Shaareiy Teshuvah 554:14 in name of Machazik Bracha
 See Piskeiy Teshuvos 554:6 in name of Chazon Ish that she does not need to try giving him formula and the like, as mother’s milk is the healthiest food for a child. However, certainly if the child has already been given formula before, and consumed it, then she must try to do so for Tisha B’av as well.
 554:6; For a further understanding of such cases see Admur 617-618
 Michaber ibid
 Rama ibid; M”B 554:14
 Rama ibid
 Aruch Hashulchan 554:8 “Today heaven forbid a woman after birth to fast on Tisha B’av as they are weak and are certainly sick and therefore they are not be allowed to fast”; Pnei Yehoshua 2:16; Avnei Nezer 540; Shevet Halevi 6:70 that by Tisha B’av Nidche they are not to fast; Piskeiy Teshuvos 554:7; so I received also from Rav Asher Lemel Hakohen
 Chayeh Adam 135:2; Kitzur SHU”A 124:6; Divrei Yatziv 233 [as today women are more healthy than in previous times]
 M”B 554:13
 Shvus Yaakov 3:37; Hagahos Rav Akiva Eiger 559:9; Biur Halacha 559 “Eino”; Nitei Gavriel 65:3; Piskeiy Teshuvos 554:5; See Yechaveh Daas 3
 Nitei Gavriel 65:3
 From when is a woman considered pregnant in this regard? There is no difference in this regard whether she is in the beginning or end of her pregnancy. [M”B 617:1] The laws of fasting relevant to a pregnant woman begins to apply from the moment she knows she is pregnant, even if this is prior to the passing of 40 days from the time of conception. [Daas Torah 617:1; Sheivet Halevy 7:80; Nitei Gavriel 38:4] However, there are Poskim who question whether prior to 40 days we allow her to break her fast to prevent miscarriage. [Shaar HaTziyon 617:1; See also M”B 550:3; Kaf Hachaim 550:5]
 Ruling of Rav Asher Lemel Cohen and Rav Yaakov Yosef
 See M”B 617:9; Mamar Mordechai 617:3; Alef Lamateh 617:5; Sdei Chemed 3:2; Meishiv Halacha 242; Minchas Yehuda 29; Nitei Gavriel 38:5; Regarding that the above applies only after 9 months: So ruled Rav Yaakov Yosef and Rav A. L. Cohen
 According to Halacha, a child is considered premature, and an 8th month child, until nine full months have passed from conception. [See Y.D. 374:8; See Meil Tzedaka 5, brought in Pischeiy Teshuvah 374:9 that we follow the Hebrew months in this regard, and not an amount of weeks or days. Thus, since the months vary between 29 and 30 days, determining how many weeks:days need to pass depends on how many days were in each of the nine months of her pregnancy. If, for example, there were five 30 day months and four 29 day months, then it is exactly 38 weeks, which is 266 days. If however there were more or less than five 30 day months, then it would be more or less than 38 weeks. Thus, we determine the completion of nine months based on the passing of Hebrew months, and not based on weeks or days.] Medically, however, a child is only considered premature if born prior to week 37 from her last period, which is approximately week 35 from conception. Nonetheless, a child born in week 37-38 from the last period is termed an “early term baby” and quite often the child is not yet developed enough to be born. It is only considered full term in weeks 39-40 from the last period, which fits the Halachic definition of 37-38 weeks from conception.
 See Poskim ibid that compare a woman giving birth to a regular Yoledes within three days, of which the law is that she may eat regularly.
 Piskeiy Teshuvos 317:1 footnote 3; Rav A. L. Cohen
The reason: As there is no danger involved for her or the child if she gives birth in her 9th month, and hence there is no reason to permit her to eat in order to stop contractions.
 Elya Raba brought in M”B 554:16
 Piskeiy Teshuvos 554:9
 Avnei Nezer 540; Kaf Hachaim 556:9; Minchas Yitzchak 8:30; Kinyan Torah 2:111; Piskeiy Teshuvos ibid and 556:4
 Kaf Hachaim ibid; Poskim ibid
 Tzemach Tzedek O.C. 108:110; Divrei Nechemia 42; Sefer Haminhagim p. 92 [English]; Halachos Ketanos 2:100; Maharam Shick 289; Shaiy Lamorah 4; Marcheshes 1:14; Biur Halacha 554 “Bemakom” in name of Pischeiy Olam
 Chida in Machazik Bracha, brought in Kaf Hachaim 554:31; Maharam Shick 290; Avnei Nezer 540; Aruch Hashulchan 554:7
 Shevet Halevi 4:56; Kinyan Torah 1:118; Tzitz Eliezer 10:25-16; Shraga Hameir 1:59; Piskeiy Teshuvos 554:9; Hiskashrus 889 that so he received from several Rabbanei Anash, despite the ruling in Sefer Haminhagim ibid
The reason: Some suggest the entire reason behind the Shiurim recorded in the previous Poskim who are stringent is order to also gain the advantage of being considered to have fasted, and hence be able to count for a Minyan for Kerias Hatorah, and saying Aneinu and the like, however not that one is required to follow these Shiurim. [See Hiskashrus ibid; Piskeiy Teshuvos ibid and 566:6; Marcheshes ibid]
 Chasam Sofer 157; Maharil Diskin 75
 Orchos Chaim Spinka in name of Neziros Shimshon; Shevet Hakehasi 2:190; Piskeiy Teshuvos 554:9
 Ashel Avraham 686 Mahadurah Tinyana
 Kaf Hachaim 554:34 in name of Kesonos Yosef 4; Ikarei Hadaat 29:36; Tosefes Chaim on Chayeh Adam 1:135-8; Piskeiy Teshuvah 567; Pischei Olam 554:6; Piskeiy Teshuvos 554:7; 568:3; See also regaridng Yom Kippur: Sdei Chemed Yom Kippur 3:8; Yeshuos Yaakov 612; Kesav Sofer 111; Pischeiy Teshuvah Y.D. 155:6; Shoel Umeishiv Mahdura Daled 1:55; Orchos Chaim 618:1; Eretz Tzevi 88; Igros Moshe 3:91; Tzitz Eliezer 10:25; SSH”K 39:8; Nishmas Avraham 612:7; Piskeiy Teshuvos 612:2; Nitei Gavriel 37:23; 39:12-15
 Igros Moshe 3:91; Piskeiy Teshuvos ibid
 Kneses Hagedola 2:71; Birkeiy Yosef 556:3; Zechor Leavraham 556:9; Shaareiy Teshuvah 556:1; Moed Lekol Chaiy 49; Kaf Hachaim 556:9
 Divrei Malkiel 6:9; Piskeiy Teshuvos 556:4 as is the ruling by an Avel; Regarding an Avel-see Pischeiy Teshuvah 376:2; 391:1 Piskeiy Teshuvos 296:6
 Birkeiy Yosef ibid; Shraga Hameir 7:71; Az Nidbaru 11:48
 Kaf Hachaim 556:9; Minchas Yitzchak 8:30; Kinyan Torah 2:111
 Kaf Hachaim ibid
 Admur 616:9
 Admur 616:9; Elya Raba 549:7; Kaf Hachaim 550:1
Two hairs: The above law only applies if the child has reached puberty which means that he or she has grown two pubic hairs. If the child has reached this age, but does not have two pubic hairs, then although he or she must keep all the commands out of doubt that perhaps he or she grew the hairs and they fell off, nevertheless the child is not required to fast any of the Rabbinical fasts. [Admur ibid]
Other Poskim: Some Poskim rule the child must fast even the Rabbinical fasts once he or she reaches 13:12 even if the child has not yet grown two hairs. [P”M 550 A”A 2; Biur Halacha 550 “Hakol”; Kaf Hachaim ibid]
 Admur 616:9; Elya Raba 549:7; M”B 550:5; Kaf Hachaim 550:1
 There is no source in Poskim for educating a child to fast the three fasts prior to his Bar:Bas Mitzvah. On the contrary, it is forbidden to force the child to do so, if they do not desire to fast. On the other hand, if they desire to fast, there is no need for the parent to stop them.
 Chayeh Adam 133:6; M”B ibid; Kaf Hachaim 550:9; Piskeiy Teshuvos 550 footnote 10
Other Opinions: Some Poskim rule that children [of nine years old] are to be educated to fast for a few hours into the day just as is the law on Yom Kippur, as rules Admur 616:5. [see Poskim in next footnote]
 Erech Hashulchan 554:2 and Beis Hillel brought in Kaf Hachaim 554:23; Siddur Yaavetz; Chanoch Lenaar 21 footnote 9; Beir Moshe 8:98; Piskeiy Teshuvos 554:9 that so is the custom; Nitei Gavriel 64:2
 Both boys and girls.
 Such as if they normally eat at 2:00 they are to eat at 3:00 and so on and so forth in accordance to the amount of delay that the child can handle. [Admur 616:5]
 Admur 616:10 regarding even Yom Kippur
 M”A 550:2; Rameh 111; P”M 549 A”A 7; Chayeh Adam ibid; M”B ibid; brought in Kaf Hachaim 549:8 and 550:9
 Some write this is starting from age nine. [See Piskeiy Teshuvos 550 footnote 11]
 Birkeiy Yosef 549:1; Daas Torah; Kaf Hachaim 549:8 and 550:9; Beir Moshe 8:95
 Beir Moshe ibid; Piskeiy Teshuvos 550:3
 Nitei Gavriel 64:1
 Kaf Hachaim 554:53 in name of Tosefes Chaim 155:10
 I have not found this explicit in the Poskim. However see Nitei Gavriel 64:2 for a similar ruling; See also Likkutei Dibburim, vol. 4, p. 1418 that the Rebbe Rashab allowed his son to fast on Yom Kippur from age seven!
 See Piskeiy Teshuvos 556:4
 Divrei Yatziv 243
 SSH”K 62:45; Nitei Gavriel 95:7
 Divrei Malkiel 5:130; Yad Sofer 7; See Yad Efraim on M”A 554:9
 Maharsham 3:363; Avnei Nezer 426; Mishneh Sachir 2:147
 Nitei Gavriel 64:5
 Rama ibid; M”A 557:1; Beis Yehuda 2:87; Chayeh Adam 135:23; Admur 618:8 and Michaber 618 regarding Yom Kippur
Other opinions: Some Poskim question whether Nachem is to be recited and rule it is not to be said. [Taz 618 regarding Yom Kippur; Elya Raba 557:3; Birkeiy Yosef 557:2 in name of Poskim; Shaareiy Teshuvah 557:1; M”B 557:5; Kaf Hachaim 557:11 concludes it is not to be said prior to Boneh Yerushalayim, but rather prior to Harachaman] Other Poskim rule it is only to be recited from the time of Mincha and onwards. [Ben Ish Chaiy Devarim]
 M”A 557:1; M”B 557:5
 M”A 557:1; Chayeh Adam 135:3
 Shaar Hakolel 34:9
 Piskeiy Hasiddur 185; See however M”B ibid Kaf Hachaim ibid and Hiskashrus 889 who writes it is to be recited in Harachaman, See Nitei Gavriel Bein Hametzarim 66:11
 Siddur Yaavetz; Nitei Gavriel 66:11
 Kaf Hachaim 554:53 in name of Tosefes Chaim 155:10