The Laws of Rosh Chodesh

• One should not fast on Rosh Chodesh, even if the fast is intended for just a few hours.1
• Although there is no obligation to wash and eat a meal in honor of Rosh Chodesh, one should endeavor to increase in what is eaten on Rosh Chodesh, in honor of this day, and even to include bread during the meal.2
• One should not take a haircut on Rosh Chodesh, even if it comes out on Friday and the haircut will be taken in honor of the Shabbat.3
• One should also avoid cutting nails on Rosh Chodesh.4
• If a child turns three years old on Rosh Chodesh, the upsherenish (cutting of the hair at the age of three) should take place right after Rosh Chodesh, and not on the day itself.5

Grace After Meals

• In the Grace After Meals, we add the paragraph beginning Yaaleh v’yavo (“May there ascend . . .”) in the third blessing. (For the text of the Grace After Meals, click here.) If one forgets to say Yaaleh v’yavo and realizes his error before saying G‑d’s name at the end of the paragraph beginning Uv’nei yerushalayim (“And rebuild Jerusalem . . .”), Yaaleh v’yavo can still be recited there. If, however, you already said G‑d’s name, conclude the blessing and then add these words:
  

  Transliteration: Baruch a‑toh A‑do‑noi Elo‑hei‑nu me‑lech ha‑o‑lam she‑na‑san ro‑shei cho‑da‑shim le‑a‑mo yis‑ra‑el le‑zi‑ka‑ron.

  Translation: Blessed are You, L‑rd our G‑d, King of the universe, who has given the days of Rosh Chodesh to His people Israel for remembrance.

• If you already said the first word of the fourth blessing, continue with Grace, and it is not necessary to repeat it.

The Prayers

• On Rosh Chodesh we recite the “half Hallel.” The chazzan (cantor) should say the blessing at the beginning and the end of Hallel and thereby exempt all the congregants, and the congregants should answer “Amen” and thus be included within the blessing.6 If a person is praying alone, without a minyan, he or she should recite the blessing.
• The special Rosh Chodesh Musaf is recited.
• We insert Yaaleh v’yavo in the Amidah of the Shacharit, Minchah and Maariv prayers of Rosh Chodesh. It is inserted in the blessing of Retzei (“Look with favor . . .”). If you inadvertently omitted Yaaleh v’yavo and realized this error before pronouncing G‑d’s name in the blessing Hamachazir shechinato letzion (“Who restores His Divine Presence to Zion”), return to Yaaleh V’yavo and say it.
• If, however, you realize your error after pronouncing G‑d’s name, the following rules apply for Shacharit and Minchah:
  
  1. If you realize the error right after saying G‑d’s name, add the words lamdeini chukecha (“Teach me Your statutes”), and then return to Yaaleh V’yavo.7
  2. If you already said hamachazir, but did not start the Modim (“We thankfully acknowledge . . .”) blessing, you can say Yaaleh v’yavo there, and continue with Modim.
  3. If you already started Modim, and realized your omission before completing the line Yihyu leratzon . . . vego’ali (“May the words . . . and my Redeemer”) at the end of the paragraph beginning Elokai netzor (“My G‑d, guard . . .”), return to the blessing of Retzei and continue from there.
  4. If you already finished saying Yihyu leratzon, even though you did not take the three steps backward, you must return to the beginning of the Amidah.
• During Maariv, however, once you have recited G‑d’s name in the blessing Hamachazir, you cannot avail yourself of any of the options mentioned above. Simply finish the Amidah, and do not repeat it.