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A. Ya’aleh Veyavo:
On Rosh Chodesh one recites Ya’aleh Veyavo within Birchas Hamazon.
Where to recite it: It is recited within the blessing of Boneh Yerushalayim. If one recited Ya’aleh Veyavo in the blessing of Birchas Haaretz he does not fulfill his obligation and it must be repeated in the blessing of Boneh Yerushalayim.
Saying the phrases aloud and answering Amen:
On Rosh Chodesh, when the person leading the Bentching says Ya’aleh Veyavo, he is to raise his voice slightly while reading the following three phrases: 1) Zachreinu Bo Letova; 2) Ufakdeinu Vo Levracha; 3) Vehoshieinu Vo Lechaim Tovim. At the end of each of the above phrases those who are present answer Amen. One does not respond Amen after the word Yechasreinu.
If the listener is not holding by Ya’aleh Veyavo, may he answer Amen to the above phrases?
If the listener is not holding by Ya’aleh Veyavo upon the leader of the Bentching reciting the above phrases, then if he is holding between the paragraphs he may answer Amen. [It is disputed as to what is defined as between the paragraphs regarding this matter. After saying Boneh Yerushalayim, one may answer Amen to the above phrases anywhere in middle of the fourth blessing.]
B. Harachaman and Migdol:
Harachaman: After Mimarom Yilamdu one recites the Harachaman of Rosh Chodesh.
Migdol: When reciting Birchas Hamazon on Rosh Chodesh one recites “Migdal” as opposed to “Magdil”.
C. Meiyn Shalosh:
One mentions Rosh Chodesh within the after blessing of Meiyn Shalosh. It is mentioned prior to the words “Ki Ata Hashem Tov”.
Forgot to recite: If one forgot to mention Rosh Chodesh in Meiyn Shalosh he nevertheless fulfills his obligation, just as is the law regarding Birchas Hamazon, as explained next.
Remembered prior to Baruch Ata Hashem: If one remembered to mention Rosh Chodesh in Meiyn Shalosh prior to reciting the concluding blessing of “Baruch Ata Hashem”, some Poskim rule one is to retract and recite the addition of Rosh Chodesh.
D. Forgot to recite Ya’aleh Veyavo in Birchas Hamazon:
If one forgot to recite Ya’aleh Veyavo he is not required to repeat Birchas Hamazon.
Remembered after beginning the 4th blessing: If one forgot to say Ya’aleh Veyavo in its set area, and he remembered only after he already began the first word “Baruch” of the blessing of Hatov Vehameitiv, then he has fulfilled his obligation, and Birchas Hamazon is not to be repeated. [He is not to recite any extra blessing on behalf of Rosh Chodesh and is rather to continue as usual.] In such a case, it is not customary to recite Ya’aleh Veyavo in the Harachamans.
Remembered after the blessing of Uvinei Yerushalyim, but prior to beginning Hatov Vehameitiv: If he remembered prior to beginning even the first word of the blessing of “Hatov Vehameitiv” then he is to recite the blessing of Baruch [Ata Hashem Elokeinu Melech Haolam] Shenasan Roshei Chodoshim Leamo Yisrael [Lezikaron]”. This applies even on the night of Rosh Chodesh. If however it is already after sunset of the day of Rosh Chodesh, then he should not recite this blessing, even if he did not yet begin the fourth blessing. [If however it is after sunset of the first day of Rosh Chodesh, then this blessing is to be recited.]
E. Ya’aleh Veyavo on Rosh Chodesh that coincides with Shabbos:
In the event that Rosh Chodesh falls on Shabbos one is to say Ritzei and Ya’aleh Veyavo.
Forgot both Ritzei and Ya’aleh Veyavo and remembered before beginning Hatov Vehameitiv: If one forgot to say both Ritzei and Ya’aleh Veyavo and remembered prior to beginning the word Baruch of Birchas Hatov Vehameitiv then he is to say the extra blessing for Shabbos and include in it Rosh Chodesh. One is to also conclude the blessing with the mention of Rosh Chodesh. The following is the Nussach to be said:
ברוך אתת ה’ אלקינו מלך העולם שנתן שבתות למנוחה לעמו לשראל באהבה לאות ולברית וראשי חדשים לזכרון. ברוך אתת ה’ מקדש השבת וישראל וראשי חדשים.
Forgot only Ritzei or only Ya’aleh Veyavo and remembered before beginning Hatov Vehameitiv: If one said Ya’aleh Veyavo but forgot to say Ritzei and remembered prior to beginning the word Baruch of Birchas Hatov Vehameitiv then he only mentions the additional blessing of Shabbos and does not include within it the mention of Rosh Chodesh. [If one said Ritzei but forgot to say Ya’aleh Veyavo then if he remembers prior to saying Baruch of the fourth Bracha then he only mentions the additional blessing of Rosh Chodesh and does not include within it the mention of Shabbos.]
Forgot Ya’aleh Veyavo and remembered after beginning the 4th blessing: If one said Ritzei but forgot to say Ya’aleh Veyavo and remembered only after saying Baruch of Hatov Vehameitiv then he is to continue as usual and does not need to repeat Birchas Hamazon.
Forgot Ritzei and remembered after beginning the 4th blessing: If one said Ya’aleh Veyavo but did not say Ritzei, [or he omitted both Ritzei and Ya’aleh Veyavo], and remembered after saying the word “Baruch” of the fourth blessing, or after completing Birchas Hamazon, then he must retract to the beginning of Birchas Hamazon and recite both Ritzei and Ya’aleh Veyavo. He must repeat Ya’aleh Veyavo together with Ritzei in his second Birchas Hamazon even if he recited it in his original Birchas Hamazon.
What is he to do if he remembers to say Ya’aleh Veyavo in the midst of the Bracha of “Boneh Berachamav Yerushalayim”?
What is the law if one forgot to say “Vezachreinu Letova” in Meiyn Shalosh [Al Hamichya; Al Hapeiros; Al Hagafen]?
F. Began a meal on Erev Rosh Chodesh and is reciting Birchas Hamazon on Rosh Chodesh:
If one began eating a meal during the day of Erev Rosh Chodesh [before sunset] and concluded the meal at night after Rosh Chodesh has begun, then if he ate a Kezayis of bread after nightfall he is to recite Ya’aleh Veyavo in Birchas Hamazon. If he did not eat a Kezayis of bread after nightfall, he is not to recite Ya’aleh Veyavo in Birchas Hamazon.
Rosh Chodesh that falls on Motzei Shabbos: If one began eating a meal on Shabbos Erev Rosh Chodesh, such as Shalosh Seudos, and the meal ended after nightfall after Rosh Chodesh already begun, then if he did not eat a Kezayis of bread after nightfall he is to say only Ritzei and not Ya’aleh Veyavo in Bentching. If however he ate a Kezayis of bread past nightfall then he is to recite both Ritzei and Ya’aleh Veyavo.
Davened Maariv or said Havdala on Motzei Shabbos Rosh Chodesh: If one recited Havdala or Davened Maariv on Motzei Shabbos prior to Bentching, then Ritzei is not to be said, and hence if one ate a Kezayis after nightfall he is to only recite Ya’aleh Veyavo. If one said Baruch Hamavdil prior to Bentching, it receives the same law as one who Davened Maariv and hence Ritzei may not be recited.
If one Davened Maariv after Plag Hamincha on Erev Rosh Chodesh and then ate a meal, is Ya’aleh Veyavo to be recited?
If one ate bread during Bein Hashmashos of Erev Rosh Chodesh-Rosh Chodesh, is he to say Ya’aleh Veyavo?
If he ate a Kezayis of bread after nightfall then Ya’aleh Veyavo is to be recited. If however the Kezayis was only eaten during Bein Hashmashos, then it is questionable as to whether Ya’aleh Veyavo is to be recited.
G. Began a meal on Rosh Chodesh and is reciting Birchas Hamazon on Motzei Rosh Chodesh:
If one began a meal on Rosh Chodesh and the meal extended into the night after [i.e. Motzei Rosh Chodesh] one is to nevertheless recite Ya’aleh Veyavo in Birchas Hamazon.
Davened Maariv: If one Davened Maariv prior to Benching then he may no longer say Ya’aleh Veyavo in Benching. This applies even if it is still day, such as he Davened Maariv prior to nightfall, after Plag Hamincha. [Thus, one is to avoid Davening Maariv prior to Benching in order so he is able to say Ya’aleh Veyavo.]
Rosh Chodesh fell on Erev Shabbos and the meal continued into Shabbos: If one ate a Kezayis of bread on Rosh Chodesh which is Erev Shabbos and he continued the meal into Shabbos and ate a Kezayis of bread after Kiddush, then he is to only say Ritzei and omit Ya’aleh Veyavo. [See footnote regarding Chabad custom] If one did not eat a Kezayis of bread after Kiddush then only Ya’aleh Veyavo is recited. Regarding the laws of Pores Mapa Umikadesh-See The Laws and Customs of Erev Shabbos Chapter 5 Halacha 1C!
If one Davened Maariv after Plag Hamincha on Rosh Chodesh and then ate a meal, is Ya’aleh Veyavo to be recited?
No, as stated above!
What is the law if during the week one started saying Ya’aleh Veyavo?
If one remembered before finishing the Bracha he is to repeat from the beginning of that Bracha. If he remembered after finishing the Bracha he is nevertheless Yotzei.
If one ate bread during Bein Hashmashos of Rosh Chodesh-Motzei Rosh Chodesh, is he to say Ya’aleh Veyavo?
If he ate a Kezayis of bread before sunset then Ya’aleh Veyavo is to be recited. If however the Kezayis was only eaten during Bein Hashmashos, then Ya’aleh Veyavo is not to be recited.
If one began eating Mezonos or Shiva Minim or wine on Rosh Chodesh and is reciting Meiyn Shalosh on Motzei Rosh Chodesh, is Rosh Chodesh to be mentioned in Meiyn Shalosh?
 424/1; Admur 188/6
 Michaber ibid; Admur ibid; Brachos 49a; Rav in Shabbos 24a
The reason: As also Rosh Chodesh contains holiness as is seen from the fact it contains a Karban Musaf. [Admur ibid]
Other opinions in Gemara: Rav Chanina in Shabbos is of the opinion that one does not recite Ya’aleh Veyavo in Birchas Hamazon.
 Admur ibid; M”A 188/5; Elya Raba 188/5; Brachos 48b
 The reason: The recital of Ya’aleh Veyavo is a merciful request from Hashem. It was therefore positioned in the blessing of Boneh Yerushalayim, which is also a blessing of merciful request. It was not positioned in Birchas Haaretz as was Al Hanissim on Chanukah and Purim, being that they are a thanksgiving [and not a request] [Admur ibid]
 Sefer Haminhagim p. 45 [English]; Glosses of Rebbe in Haggada Shel Pesach p. 41; Letter of Rebbe printed in Shulchan Menachem 1/331 that this custom [of answering Amen on these phrases] dates back to a directive of the Rebbe Rayatz and was followed by the Rebbe Rashab.
 The following Poskim write that Amen is to be recited by Chazaras Hashatz after this statement: Elya Raba 4202/1; implication of Abudarham; Kaf Hachaim ibid; Sefer Haminhagim ibid
Other opinions: Some write that one is not to answer Amen between Zachreinu Bo Letova and Ufakdeinu Vo Levracha, as they both are going on a male and female, and therefore should not have an interval made between them. [Tolaas Yaakov; Kneses Hagedola 422/1; brought in Kaf Hachaim ibid]
 The reason it is not considered an interval: The reason that this is allowed is because it is relevant to the Bentching, and hence is no different than asking for the salt or for the bread after washing. [letter in Shulchan Menachem ibid; See Admur 167/9]
 Likkutei Sichos 24/380 [printed in Shulchan Menachem 1/331] in answer to a question posed by Rav Moshe Levertov
Other opinions: Some Poskim rule one is not to answer Amen on the above phrases due to it being an interval. [Tzelusa Deavraham 2/528 in name of Likkutei Maharich]
 Some say it refers to between Al Hamazon and Nodeh Lecha, or Al Hamazon and Racheim; or after Boneh Yerushalayim. [So explains Likkut Dinei Rosh Chodesh 5 footnote 24, and so is implied from the wording, as well as from the letter published in Shulchan Menachem ibid] However, many write that one may not make an interval between the paragraphs, being that Birchas Hamazon is like Shemoneh Esrei [see Admur 183/11] and the Rebbe’s intent is to say that one may answer Amen between Ya’aleh Veyavo and Uvinei Yerushalayim [Hefsek Betefila p. 170] or within Ya’aleh Veyavo itself. [Rav Moshe Levertov in Yagdil Torah, brought in Hefsek Betefila ibid] or that one may only make an interval between the 3rd and 4th blessing. [Hiskashrus 652, brought in Hefsek ibid]
 See Admur 183/11; 188/2; Ketzos Hashulchan 55 footnote 35; Chikrei Halachos 8/65; Binyan Olam 5; Likkut Dinei Rosh Chodesh 5 footnote 24
 Siddur Admur
 Admur 189/7 and Siddur Admur; M”A 189/1; Abudarham Seder Birchas Hamazon; Mateh Moshe 351; Kneses Hagedola 189; Ben Ish Chaiy Chukas 19
 Siddur Admur; Michaber 208/12
Other opinions: Some Poskim rule there is no need to mention Meiyn Hameura in Meiyn Shalosh. [See Beis Yosef 208; Machatzis Hashekel 208/18; Shaar Hatziyon 208/60]
 Siddur Admur; Ateres Zekeinim 208; M”B 208/59
Why do we not mention Rosh Chodesh prior to Yerushalayim, as done in Birchas Hamazon? See Shaar Hakolel 34/17; Glosses of Rebbe Rashab; Likkut Dinei Rosh Chodesh 5 footnote 28
 M”A 208/18; M”B 208/58
 Mamar Mordechai 84; Gloss in Chesed Lealafim 208/9 [brought in Kaf Hachaim 208/67]
Other Poskim: The Elya Raba ibid implies one is not to go back if he already said the words “Ki Ata Tov”. [brought in Kaf Hachaim ibid]
 Michaber 424/1; Admur 188/10; Siddur Admur
 The reason: As the [eating of a meal and subsequent] recital of Birchas Hamazon on Rosh Chodesh is voluntary, as it is permitted to simply eat fruits and the like in order to avoid fasting, and one is not required to eat bread. [Admur ibid]
 Admur 188/9; Siddur ibid; Ketzos Hashulchan 47/3; Tehila Ledavid 188/4
Other opinions: Some Poskim rule one may still recite the added blessing [brought next] so long as he has not yet said the word “Hakeil”. [Chayeh Adam brought in M”B 188/23; In the Biur Halacha he leaves this ruling with a “Tzaruch Iyun Gadol”, however he implies that simply the words Baruch Ata, in his opinion, is not problematic.
 Admur 188/12; Rama 188/7
The reason: Although regarding Al Hanissim we rule that if one forgot to mention it in Birchas Haaretz, he is to mention it within the Harachamans, nevertheless regarding Ya’aleh Veayavo the custom is not to do so. The reason for this is because the prayer of Ya’aleh Veyavo includes names of Hashem, and people did not want to mention the names if there is no requirement to do so. However, in truth, there is no prohibition in saying Ya’aleh Veayavo with Hashem’s name, as throughout the day we say prayers and supplications that include the name of Hashem. The above prohibition only applies when mentioning the name of Hashem in vain, or in an unnecessary blessing. [Admur ibid; See M”A 188/11]
 Michaber ibid; Admur 188/10; Siddur ibid
 Admur ibid and Siddur Admur
 Admur ibid and Siddur Admur
 The concluding Nussach: It is questionable as to whether one should conclude this blessing with the words “Baruch Ata Hashem Mikadesh Yisrael Veroshei Chodashim.” Practically, Safek Brachos Lihakel and therefore one should not recite it. [Admur ibid and so rules Admur in his Nussach in Siddur]
The reason an extra blessing is recited even though by Maariv we don’t add any extra blessing: Although by Maariv of Rosh Chodesh we rule that we do not require a repetition if he omitted Ya’aleh Veyavo in Avoda, and this applies even if he remembered before beginning the next blessing, nevertheless by Birchas Hamazon we rule he is to recite this blessing. The reason for this difference is because by Shemoneh Esrei one cannot repeat the Avoda if he forgot Ya’aleh Veyavo, as the Sages did not require one to do so being that the month was not sanctified at night. Likewise, one cannot recite it between Avoda and Modim, as this is considered an interval in the prayer. However, by Birchas Hamazon, after concluding Boneh Yerushalayim the Biblical Nussach has been completed and there is thus no worry of interval if one now recites a blessing mentioning Rosh Chodesh, prior to beginning the blessing of Hatov Vehameitiv. Now, although at the night of Rosh Chodesh we do not make one repeat a blessing in order to gain Ya’aleh Veyavo, nevertheless this is not a repetition but an additional blessing that the Sages established to be recited in an area that does not pose a Halachic issue of an interval. [Admur ibid]
 Admur 188/10; Michaber 188/7; Rashba Brachos 29a; Mordechai Brachos 177
The reason: Even during the Birchas Hamazon said during the night of Rosh Chodesh, if he remembered to say Ya’aleh Veyavo prior to starting the 4th blessing of Hatov Vehameitiv, he is to say the added blessing for Rosh Chodesh. Now, although by Maariv Shemoneh Esrei one does not repeat the Davening if he forgot to say Ya’aleh Veyavo in Avoda, and this applies even if he remembered prior to beginning the next blessing, nonetheless, by Birchas Hamazon, he needs to say the added blessing of Baruch Ata Hashem Elokeinu Melech Haolam Shenasan etc. The reason for this is because since by Shemoneh Esrei if he remembered only after beginning Modim the Sages did not require him to retract to return to the blessing of Avoda to mention Rosh Chodesh in the area that the Sages instituted, being that the month is not sanctified at night, therefore he is also not to mention it [i.e. Ya’aleh Veayavo] between Avoda and Modim, as doing so is an interval in the prayer. However, in Birchas Hamazon, after completing the blessing of Boneh Yerushalayim the Biblical Birchas Hamazon has been completed. There is thus no need to worry of making an interval of this blessing prior to beginning the 4th blessing of Hatov Vehameitiv. Now, although we do not make one repeat the prayer [even of Shemoneh Esrei] by the night of Rosh Chodesh, nevertheless this is not a repetition but rather an additional blessing which the Sages instituted to add in an area where there is no worry of making an interval. [Admur ibid; See Levush 188/7-8; Taz 114/12] In other words: Ideally even by the night Rosh Chodesh the Sages desired that one mention Rosh Chodesh and even say the additional blessing for this purpose, however this only applies if doing so will not pose an interval in the prayer. Hence, by Birchas Hamazon, where there is no interval, this blessing may be done while in Shemoneh Esrei, since it would pose an interval, the blessing cannot be said.
 Siddur Admur; Ketzos Hashulchan 47/3-4 and footnote 9; Tehila Ledavid 188/4; Biur Halacha 188 “Mazkir”
The reason: As there are opinions who rule that on Motzei the day one is not to mention at all that days Kedusha [see Admur 188/17] and therefore we rule Safek Brachos Lihakel when it comes to adding another blessing after sunset. [Biur Halacha ibid; Ketzos Hashulchan ibid] Alternatively, perhaps all opinions agree that an extra blessing should not be recited after sunset, and they only argue regarding if one should add the regular Nussach after sunset. [Ketzos Hashulchan ibid]
 Pashut, as it is still Rosh Chodesh, and hence fulfills all the aspects required by the Poskim in order to mention Meiyn Hameura, that both the meal and the Bentching be at a time that it is Rosh Chodesh. Furthermore, one cannot argue that it is two days due to Sfeika Deyoma, and hence if the day was Rosh Chodesh then the night is not, and if the night is Rosh Chodesh then the day was not, as in truth the two days of Rosh Chodesh are not Sfeika Deyoma at all, but rather a two day Holiday with the same status, and hence there is no reason according to any opinion for why one should not say Ya’aleh Veyavo, or the additional blessing, when his meal enters the next night of Rosh Chodesh!
 Admur 188/13; Siddur Admur; Michaber 188/7; Tosafus Brachos 49a
 Mentioning Shabbos in Ya’aleh Veyavo or Rosh Chodesh in Ritzei: According to all opinions, Shabbos is not mentioned within the recital of Ya’aleh Veyavo and Rosh Chodesh is not mentioned within the recital of Ritzei. [Admur 188/6; 487/5; Michaber 188/5; Semag 27] The reason for this is because during Birchas Hamazon, once Ritzei has been recited, the mentioning of Shabbos has concluded. [Admur 188/6] Alternatively, the reason is because since one already said Ritzei on behalf of Shabbos, there is no reason to mention it again, as also Rosh Chodesh is only mentioned one time in Birchas Hamazon. Ya’aleh Veyavo was established in Birchas Hamazon specifically for the sake of Rosh Chodesh alone and not for the sake of Shabbos, just as Ritzei was established in Birchas Hamazon for the sake of Shabbos alone and not for the sake of Rosh Chodesh. [Admur 487/5 regarding Yom Tov]
 Admur 188/6
The reason: The day of Shabbos is holier and more common than Rosh Chodesh and hence receives precedence. [Admur ibid]
 M”B 188/13; Ketzos Hashulchan 47/6 and footnote 13
Other opinions: Some Poskim rule one is required to repeat Ya’aleh Veayavo after Ritzei. [Levush 109, brought in Ketzos Hashulchan ibid footnote 13-See There]
 Admur ibid; M”A 188/14; Divrei Chamudos 76; See also Even Haozer; Michaber 208/18; Taz 208/19; Seder Birchas Hanehnin 1/20
The reason: Although above we stated that one is not to conclude with a blessing of Rosh Chodesh in the added blessing, this is because it is a doubt as to whether one is to conclude with a blessing of Rosh Chodesh and hence we apply the rule of Safek Brachos Lihakel. However here that one is in any event saying a concluding blessing on behalf of Shabbos, then he is to include with it also Rosh Chodesh, [as there is no question here of a blessing in vain, and he is able to be stringent regarding the doubt]. [Admur ibid]
 Siddur Admur; See Admur 188/13 for a shorter Nussach mentioned
 Admur 188/13; M”A 188/13; Beir Hagoleh; Ketzos Hashulchan 47/6; Sefer Haminhagim p. 129 [English] regarding Rosh Hashanah
 Admur 188/14; Michaber 188/7; Mordechai Brachos 176
 The reason: Although one is obligated to eat bread [on Shabbos] this obligation is only due to Shabbos, as on Rosh Chodesh there is never an obligation to [eat bread and] recite Birchas Hamazon with the mentioning of Ya’aleh Veyavo. This is similar to Maftir of Navi on Rosh Chodesh that falls on Shabbos, in which case we do not mention Rosh Chodesh [in the blessings of the Haftorah] being there is never a Haftorah on Rosh Chodesh [alone]. [Admur ibid; M”A 188/12]
 Admur 188/14; M”A 188/13; Ketzos Hashulchan 47/6
 The reason: As in every Birchas Hamazon one must mention Rosh Chodesh even though he is not repeating it for the sake of Rosh Chodesh. [ibid]
 See Piskeiy Teshuvos 597/1
 M”A 208; Elya Raba 208/20; M”B 188/22; Mamar Mordechai 84; Kaf Hachaim 208/67
Other opinions: The Ketzos Hashulchan 47/3 leaves this matter in doubt, questioning that perhaps it is better to finish the blessing and say the additional blessing of R”C rather than make an interval with a verse in Tehillim of Lamdeini Chukecha in middle of prayer.
 M”B 208/58; See Ketzos Hashulchan 47 footnote 8
 Mamar Mordechai ibid; Gloss in Chesed Lealafim 208/9 [brought in Kaf Hachaim 208/67]
Other Poskim: The Elya Raba ibid implies one is not to go back if he already said the words “Ki Ata Tov”. [brought in Kaf Hachaim ibid]
 188/17; Ketzos Hashulchan 47/9
Admur ibid records a dispute in this matter. Some opinions rule, as stated above, that one only recites Ya’aleh Veyavo if he ate a Kezayis of bread after nightfall. Others rule that even if he did not eat a Kezayis after nightfall he is to recite Ya’aleh Veyavo. Practically, the custom is like the former opinion.
 188/17; Ketzos Hashulchan 47/10 footnote 22; See M”B 188/33
 Admur ibid; Taz 188/7, brought in M”B 188/33 as 2nd opinion
Admur ibid records a dispute regarding whether one may say both the previous days and current day’s extra prayer within Bentching, if he began a meal during the day and it continued into the night, with him eating a Kezayis of bread at night. [M”A 188/18 prohibits; Taz 188/7 permits if said in order] He concludes like the Taz ibid that one may do so if the order in the Benching is that he first recites the previous day’s event and then recites the current night’s event. [Such as one who had a meal on Shabbos afternoon and Motzei Shabbos is Rosh Chodesh and Ritzei precedes Ya’aleh Veyavo.] If however the night’s event precedes the previous day’s event then one may not say both prayers even according to the lenient opinion, as it is a contradiction. One is thus to only say the current nights event. [Admur ibid; Ketzos Hashulchan ibid; Taz 188/7; brought in M”B ibid]
Other opinions: Some Poskim rule one never recites the additions of two days, as it appears contradictory, and hence on Motzei Shabbos Rosh Chodesh one only recites Ya’aleh Veyavo if a Kezayis was eaten at night. [M”A 188/18 and 419/1; 2nd opinion in Admur ibid; first opinion in M”B ibid] Others rule one is to only recite Ritzei and not Ya’aleh Veyavo. [Darkei Chaim Veshalom 307; See Shoel Umeishiv 3/1-373]
 Admur ibid; Ketzos Hashulchan 47/8
 The reason: As it is a contradiction to have prayed the prayer of the next day and then mention the previous day. [ibid]
 Admur ibid leaves this matter in question and concludes that Shev Veal Taaseh Adif, that it is better not to say it. Vetzaruch Iyun as to the intent of the parentheses there; Ketzos Hashulchan 47/8
 Magen Avraham 419/1
 The wording in Admur is “He ate a Kezayis of bread after it becomes night”; See Piskeiy Teshuvos 188/19 in name of Ashel Avraham of Butchach; This matter is a Sfek Sfeka as perhaps we rule like the opinion that says one follows the time of the Bentching, and even if not, perhaps Bein Hashmashos is night. Vetzaruch Iyun!
 Admur 188/17; Rama 695/3; Ketzos Hashulchan 47/8
Admur ibid records three opinions in this matter:
- Some opinions rule, as stated above, that one recites Ya’aleh Veyavo even after nightfall as we follow the beginning of the meal, which was eaten on Rosh Chodesh. [Hagahos Maimanis Megillah 2/14; Orchos Chaim Purim 35; First opinion Admur ibid; Michaber 188/10; First opinion in Michaber 695/3; Opinion in Shut Rama 132; Opinion in M”A 188/18]
- Others however rule that this only applies to Shabbos and Yom Tov which contain the Mitzvah of Tosefes Kedusha, however by Rosh Chodesh, Chanukah and Purim one is not to recite Ya’aleh Veyavo after nightfall as on those days there is no Mitzvah to add from Chol el Hakodesh. [Shelah Shaar Hakedusha 82b; Olas Shabbos 188/5; second opinion Admur ibid; Custom in Shut Rama 132; Opinion in M”A 188/18]
- Others rule that even by Shabbos and Yom Tov we do not recite their addition after nightfall. [Rosh 22/6; Third opinion in Admur ibid; second opinion in Michaber 695/3;]
Practical ruling: Practically, the custom is like the first opinion. [Admur ibid; Michaber 188/10; Rama 695/3; Or Letziyon 3/2-8]
Other opinions: Some Poskim rule like the second opinion above that one is not to recite Ya’aleh Veyavo after nightfall. [Ben Ish Chaiy Chukas 22; Kaf Hachaim 695/33]
 Admur ibid; Ketzos Hashulchan ibid
Other Opinions: The M”B 695/16 records a dispute on this matter and rules one is to initially avoid Davening Maariv before Birchas Hamazon in order to avoid the dispute.
 The reason: As it is a contradiction to have prayed the prayer of the next day and then mention the previous day. [ibid]
 Admur 188/17; Magen Avraham 419/1; Kaf Hachaim 424/4; See also Admur 18/8 [regarding Tzitzis]; 30/5 [regarding Tefillin]; Rama Y.D. 196/1 regarding Hefsek Taharah
 M”B ibid, now although he writes this in order to avoid the dispute. Seemingly even according to Admur it is proper to say the Kedusha of Ya’aleh Veyavo within Bentching and avoid Davening Maariv.
 Ketzos Hashulchan 48 footnote 22 based on Admur 188/17; Taz 188/7; M”B 188/33
 The reason: As one may not mention the additions of two different days if the previous day’s prayer is said after the current day’s prayer, and Ya’aleh Veyavo is recited after Ritzei. [Admur ibid; Taz ibid] Therefore, one is to recite only Ritzei, as it is disputed whether one may recite Ya’aleh Veyavo after evening, while Ritzei is an obligation according to all if he ate a Kezayis at night. [Ketzos Hashulchan ibid based on Admur ibid in the opinion of M”A 188/18 that give the same ruling regarding Motzei Shabbos that is Rosh Chodesh that in his opinion only Ya’aleh Veyavo is to be recited.] See Admur ibid in name of M”A regarding the difference between Rosh Chodesh and Purim; Ya’aleh Veyavo of Rosh Chodesh is included within the ruling of Admur and the Taz regarding Motzei Shabbos. However on Erev Shabbos they would rule that it is not said.
 Ruling of the Chabad Rabbeim: Regarding Ritzei and Ya’aleh Veyavo of Yom Tov, the Rebbe ruled, and so is the Chabad custom, to say both the prayer of the night and of the previous day even if the night prayer is said first [i.e. Yom Tov which continues into Shabbos]. This is unlike either opinion brought in Admur ibid, and is unlike the final ruling of Ketzos Hashulchan ibid. [Shaareiy Halacha Uminhag p. 211; Sichas Simchas Torah 1957; Sefer Hasichos 5704 p. 40] Nevertheless, regarding Ya’aleh Veyavo of Rosh Chodesh, it requires further analysis whether the Rabbeim would hold that one is to say both prayers even though they form a contradiction, as by Ya’aleh Veyavo of Rosh Chodesh there are opinions that rule it should not be mentioned at all after nightfall being it does not have Tosefes Kedusha, and it is hence not similar to Ya’aleh Veyavo of Yom Tov. [See Admur 188/17 that there are three levels: Chovah and Tosefes Yom [Ritzei, Ya’aleh Veyavo of Yom Tov]; Chovah-Musaf [Rosh Chodesh]; Minhag [Al Hanissim].] Nevertheless, perhaps one can learn from the above ruling of the Rabbeim that it would also apply to Ya’aleh Veyavo of Rosh Chodesh, as practically even regarding Yom Tov there are opinions that state one never recites the additional prayer after nightfall and nevertheless the Rabbeim said the Ya’aleh Veyavo of Yom Tov despite the above ruling of Admur not to recite contradictory prayers in wrong order. Hence, perhaps the same would apply also by Rosh Chodesh which although is disputed in whether it is to be recited, nevertheless is treated as an obligation. [See Admur ibid in name of M”A regarding the difference between Rosh Chodesh and Purim; Ya’aleh Veyavo of Rosh Chodesh is included within the ruling of Admur and the Taz regarding Motzei Shabbos. See Likkut Dinei Rosh Chodesh 5 footnote 21; Vetzaruch Iyun.]
 If one did not eat a Kezayis of bread after Kiddush then only Ya’aleh Veyavo is said. In such a case one must still eat a Friday night meal. If this is not possible, one is to eat three meals the next day. Once sunset has arrived one is to do Pores Mapah and is not to bentch prior to eating Kezayis.
 Ketzos Hashulchan 47/13
 Piskeiy Teshuvos 188/19 in name of Ashel Avraham of Butchach
 Shevet Hakehasi 5/42; Piskeiy Teshuvos 208/18; implication of Mamar Mordechai 288/18; implication of Admur 288/17 “Seudaso”; Implication of Elya Raba 188/20
Other opinions: See Kitzur SHU”A Lechem Hapanim 44/17 that implies one does recite Mein Hameura if he ate during the day. See also Piskeiy Teshuvos ibid footnote 145 that suggests from the Lechem Hapanim [44/17] that if one eats also at night after Rosh Chodesh then Rosh Chodesh can be mentioned. Vetzrauch Iyun Gadol on his understanding.
 The reason: As only when one has a real Kevius Seuda do we say that the after blessing follows the time of the eating, and not by a mere snack. [See Elya Raba 188/20] Alternatively, as saying Meiyn Hameura in Meiyn Shalosh is not such an obligation. [Mamar Mordechai 288/18]