From the Ravs Desk: How Does One Calculate the Onah Beinonis? Day 30 or 31 from the Period?

How Does One Calculate the Onah Beinonis? Day 30 or 31 from the Period?

Question

Does the calculation of the Onah Beinonis include the day on which the woman saw her period, or does the counting begin only from the following day? I am confused about how to calculate the Onah Beinonis. I was always taught that one counts thirty full days after the day of the period, meaning that the day on which my wife saw her period is not counted as day one. However, I later encountered opinions stating that the day of the period is counted as day one. This creates a significant practical difference, as it results in the Onah Beinonis being either one day earlier or later. What is the correct halachic ruling?

Answer

This matter is indeed the subject of a major dispute among the Poskim. The practical ruling of the Alter Rebbe (Shulchan Aruch HaRav, Hilchos Niddah), and this is also the established Chabad custom, is that the day on which the period was seen is counted as day one. As a result, the Onah Beinonis always falls four weeks later, on the next weekday from the original sighting. So is likewise ruled by the Sephardim. [According to other Ashkenazi opinions, however, the mourning period extends until the thirty‑first day, and many outside of Chabad are accustomed to be stringent and observe the Veses and Perisha on both the thirtieth and thirty‑first day. Nonetheless, the primary ruling accepted for the general Jewish community is that the Veses is on the thirtieth day, with the observance of the thirty‑first day serving merely as an added stringency for those who have an established custom to be more stringent.]

• Example: If a woman saw her period on Monday during the day: That Monday is counted as day one. The Onah Beinonis will therefore fall on Tuesday four weeks later. Thus, according to this opinion, the Onah Beinonis is not 30 days after, but rather the 30th day inclusive, which places it exactly four weeks later.

Explanation

Opinion 1 – Excluding the Day of the Period: Some Poskim understand the Onah Beinonis as requiring thirty complete days to pass after the sighting. According to this approach the day of the period is not counted and day one begins on the following day. The Onah Beinonis therefore occurs two days later than four weeks. This view understands the calculation as a waiting period of thirty full days, similar to other areas of halachah where counting begins after the initiating event.

Opinion 2: Including the Day of the Period (Alter Rebbe / Chabad Custom): The Alter Rebbe rules that the day of the sighting itself is included in the count. The reasoning is that the Onah Beinonis is not merely a waiting period, but a fixed interval based on the pattern of the cycle. Since the veset began on that day, it is halachically significant and counts as the first unit of time. According to this approach, the Onah Beinonis always falls out four weeks later on the next weekday. This ruling was accepted practically by the Alter Rebbe and remains the normative practice among Chabad Chassidim.

Opinion Three – Separate on both days: There are those who are accustomed to take both opinions into account, and therefore practice separation on both the thirtieth and the thirty‑first days.

Sources:

See Michaber Y.D. 189:1; Shiureiy Sheivet Halevi 189:1-5; Taharah Kehalacha 24:29; Nitei Gavriel 92:2

Poskim who rule that the day of the sighting counts as day one of the thirty days and hence the Onah Beinonis is four weeks later on the next weekday: Admur 189:1, 42 and Kuntrus Achron 1; Taz 189:14 and 17; Beis Yosef 189; Darkei Moshe Haruch 189:6; Bach 189:15; Perisha 189:23 and 25; Levush 189:13; Shelah Shaar Haosiyos p. 72; Chacham Tzevi 114; Kreisy Upleisy 189:15; Pardes Rimonim 189 S.C. 30; Beis Lechem Yehuda 189:11; Shoel Umeishiv Mahadurah 1 2:180; Meiy Nida Kuntrus Achron 141; Tiferes Yisrael 189:15; Piskei Dinim 189:1; Suga Beshoshanim 4:1; 5:2-3, 11; Taharas Yisrael 189:5; Or Letziyon; Divrei Yatziv 74; Even Yisrael 9:79; Mishneh Halachos Tinyana 3:138; Darkei Tahrah p. 66; Taharas Habyis 2:6; Toras Hataharah 2:3; 3:3; 16:12; Taharah Kehalacha 24 footnote 49; Rav Zalman Shimon Dworkin in Koveitz Zalman Shimon

Poskim who rule that the day of the sighting does not count as day one: Shach 189:30 and 34; Chavas Daas Chidushim 12 Biurim 14; Chasam Sofer Y.D. 155; 166 and 176; Tiferes Lemoshe 189:30; Kitzur SHU”A 155:3

Poskim who rule to be stringent to separate on both the 30th and 31^st day: Chochmas Adam 112:5; Taharas Yisrael 189:5; Lechim Vesimla 189:1, 23, 38, and 67; See Taharah Kehalacha 24:29; Many Poskim in Nitei Gavriel ibid footnote 5