When to Say Kiddush Levanah for Chodesh Tishrei - Before or After Yom Kippur?

Shalom,Every year in our minyan there’s a lively discussion about when to say Kiddush Levanah for Chodesh Tishrei. Could you please fill me in on the background of this controversy so I can better understand the different opinions and share them with others?

Thank you for your question.

The question is whether one should say Kiddush Levanah before Yom Kippur or wait until after Yom Kippur to do so.
 The ‘controversy’, as you called it, is based on a number of factors and sources in the Rishonim and Achronim. I would like to share it with you so you can later share it with the people in your shul.
 I will first give you a concise answer and then a more in-depth explanation.

There are people who have the custom to wait until after Yom Kippur in order to do Kiddush Levanah.
 The reason for this is that a person should recite Kiddush Levanah only when he is b’simchah.
 Until after Yom Kippur a person is not considered fully b’simchah, since the Sifrei Chaim and Sifrei Meisim are still open before the Ribono shel olam.
Therefore, we first wait until the Yemei HaDin are over, and then we can say Kiddush Levanah b’simchah, as it says that on Motza’ei Yom Kippur a bas kol calls out “Lech, echol b’simchah es lachmecha…

However, there are opinions that say just the opposite:
 Since between Rosh Hashanah and Yom Kippur are the Yemei Din, we try to attain as many zechuyos as we can.
Adaraba, one should recite Kiddush Levanah during the Aseres Yemei Teshuvah so that he will have another zechus in his favor.

In practice…

HaGaon HaRav Amrom Fried writes that one should follow the minhag avosav - the custom of his forefathers.

The answer in-depth:

 The Maharil, in Hilchos Aseres Yemei Teshuvah (p. 304), writes that one should recite the Kiddush Levanah of the month of Tishrei only after Yom Kippur.
This is the opinion brought by the Rema in Orach Chaim, Hilchos Rosh Hashanah, Siman 602.

שולחן ערוך אורח חיים הלכות ראש השנה סימן תרב

אין מקדשין הלבנה עד מוצאי יום כפור;

One does not recite the blessing for Kiddush levanah until Motsey Yom Kippur.

There are two reasons for this minhag 

One reason is brought by the Levush (ibid.) that one should recite Kiddush Levanah b’simchah, and during the Aseres Yemei Teshuvah one isn’t fully b’simchah, since these are Yemei Din.

The second reason is brought from the Seder HaYom (p. 118): since on Motza’ei Yom Kippur we are considered like malachim, it is therefore fitting to greet the Shechinah then.

However, the Leket Yosher (vol. 1, p. 70) writes that the Terumas HaDeshen would recite Kiddush Levanah on Motza’ei Shabbos, Shabbos Teshuvah and would not wait until Motza’ei Yom Kippur.
He did so in order that the zechus of this mitzvah should tip the scales for the good, since these are the Yemei HaDin and every mitzvah we do can change the verdict in Shamayim.

The Levush (ibid.), the Vilna Gaon in Sefer Ma’aseh Rav (os 159), and the Eliyah Rabbah all pasken like this opinion and write that the greatness of this mitzvah has the power to save someone from death, Rachmana litzlan.
The same is written by the Chidah (Moreh B’Etzbah, os 283), Rabbi Chaim Palagi (Sefer Ruach Chaim, siman 603), and likewise by the Aruch HaShulchan (siman 602, se’if 18).

The Mishnah Berurah brings both opinions and refrains from giving a direct psak as to which is l’halachah.
However, in the Biur Halachah (siman 426) it seems that he leans closer to the opinion of the Levush mentioned earlier, that one should say it before Yom Kippur.

In practice, the following communities recite Kiddush Levanah before Yom Kippur:
 the Gaon of Vilna, the Chazon Ish (Orchos Rabbeinu, vol. 1, p. 277), and minhag Yerushalayim.

However, minhag of the Artzos: Ashkenaz (Minhagei Frankfurt, p. 142), Damesek (Sefer Pri Yitzchak, os 161), and Gerbah (Brit Kehunah, os 19) is to recite it after Yom Kippur.

So, as you see it is a big controversy and therefore one should follow the minhag of his father.

Wishing you a kesivah v’chasimah tovah.

• Shulchan Aruch Orach Chaim 602
• Rema Orach Chaim 602
• Shimusha Ve'limudah page 506 (HaGaon Harav Amrom Fried Shelita)
• Maharil, Hilchos Aseres Yemei Teshuvah p. 304
• Levush (ibid.)
• Seder HaYom p. 118
• Leket Yosher vol. 1 p. 70
• Terumas HaDeshen (as quoted in Leket Yosher)
• Vilna Gaon, Sefer Ma’aseh Rav os 159
• Eliyah Rabbah
• Chidah, Moreh B’Etzbah os 283
• Rabbi Chaim Palagi, Sefer Ruach Chaim siman 603
• Aruch HaShulchan siman 602 se’if 18
• Mishnah Berurah (on Orach Chaim 602)
• Biur Halachah siman 426
• Orchos Rabbeinu vol. 1 p. 277
• Minhagei Frankfurt p. 142
• Sefer Pri Yitzchak os 161
• Brit Kehunah os 19