Days on Which Tachanun is not Recited
Question: When, and why, is Tachanun omitted?
Discussion: Many Rishonim understand that Tachanun was not instituted originally as an absolute obligation, but as an optional practice.145 Now, the Poskim tell us that eventually it was accepted by all segments of the Jewish people as obligatory and should not be treated lightly.146 Nevertheless, the obligation of reciting Tachanun is subject to custom, and it was customarily not recited on days or occasions which are festive.147
Besides for all Shabbos and Yom Tov days (including Chol Hamoed),148 Tachanun is universally omitted on the following days: Rosh Chodesh, Chanukah, Purim, Shushan Purim, and the 14th and 15th days of Adar Rishon, the entire month of Nissan, Lag Ba’omer, Tu BeShevat, Tisha Be’Av, Tu Be’Av, erev Rosh Hashanah and erev Yom Kippur, the days between Yom Kippur and Sukkos and the days from Rosh Chodesh Sivan until Shavuos.149
On the following days, most congregations omit Tachanun, but it is subject to local custom: Pesach Sheini,150 after Shavuos until the twelfth day of Sivan, after Sukkos until Rosh Chodesh Cheshvan.151
Generally, Tachanun is omitted at the Minchah immediately preceding a day on which Tachanun is omitted. However, at Minchah on the day preceding erev Yom Kippur and erev Rosh Hashanah, it is recited.152
In addition to the above list, there are times that some individual communities do not recite Tachanun, and each community should follow its custom.
145 See for instance, Tur 131 citing Rav Netrunai Gaon.
146 See Aruch Hashulchan 131:2.
147 Teshuvos Rivash 412, referenced by Darkei Moshe 131:5.
148 See Rambam, Tefillah 5:15.
149 Shulchan Aruch 131:6-7 with Mishnah Berurah.
150 Selichos of Behab are also omitted when they coincide with Pesach Sheini (Halichos Shlomo 11:4).
151 Based on Sha’arei Teshuvah 131:19; Mishnah Berurah 131, note 36; Aruch Hashulchan 131:12. The Chazon Ish’s custom was to recite Tachanun on Pesach Sheini as well as on the days following Isru Chag of Shavuos and Sukkos (Orchos Rabbeinu ad loc.).
152 Mishnah Berurah 131, note 33. Many also recite Tachanun at the Minchah preceding Pesach Sheini; see Luach Eretz Yisrael and Halichos Shlomo Tefillah 11, Devar Halachah 8.