QUESTION: This Friday is Lag B’omer. May one get a haircut on Thursday night, or must one wait until Friday morning?

ANSWER: The Rema (Shulchan Aruch, Orach Chaim 493:2) states that the Ashkenazic custom permits taking a haircut on Lag B’Omer and omitting Tachanun on that day. However, he notes that one must wait until Lag B’Omer itself and should not take a haircut on the preceding evening.

The Mishnah Berurah (493:11) cites dissenting opinions, including those of the Elya Rabba and the Chok Yaakov, who permit haircuts beginning the night of Lag B’Omer. Those who follow the stricter view maintain that since Lag B’Omer is counted among the days of mourning, leniency based on the principle of miktzas ha’yom k’kulo (a partial day counts as a full day) only applies once the daytime begins.

Those who are lenient argue that Lag B’Omer is observed as a full Yom Tov, and therefore, its sanctity applies from the night before. The Chok Yaakov points out that while the Rema would omit Tachanun only on Lag B’Omer itself, he would still recite Tachanun at Mincha on the previous day. However, since the widespread custom today is to omit Tachanun already at Mincha on the 32nd day of the Omer, this indicates that we treat the entire day of Lag B’Omer as a Yom Tov. Accordingly, taking a haircut at night may also be permissible.

Teshuvos Yehuda Yaaleh (2:39) further analyzes the Rema’s wording, suggesting that the Rema may not have required waiting until morning. Since the Rema simply wrote that one must wait until Lag B’Omer and not the evening, it is possible he was referring specifically to twilight—when the onset of the new day is uncertain—not the entire night.

Nonetheless, the preferable practice is to wait until the morning of Lag B’Omer to take a haircut, thereby avoiding any halachic uncertainty. However, if one is unable to secure a barber appointment on Friday and is concerned about appearing unkempt for Shabbos, the Kaf Hachaim (OC 493:23) writes explicitly that one may permit taking a haircut on Thursday night in honor of Shabbos.

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The Gerald & Karin Feldhamer OU Kosher Halacha Yomis is dedicated to the memory of Rav Yisroel Belsky, zt"l, who served as halachic consultant for OU Kosher for more than 28 years; many of the responses in Halacha Yomis are based on the rulings of Rabbi Belsky. Subscribe to the Halacha Yomis daily email here.