2,091. A Pattern of Eight Days

Hilchos Issurei Biah 7:21

If a woman sees blood for one impure week, which is followed by a pure week, she can engage in intimacy for 18 days, which is about one quarter of the norm. This is what the Sages meant when they said that she may engage in intimacy for one quarter of her days.

Hilchos Issurei Biah 7:22

If woman’s pattern is to see blood for eight impure days, which are followed by eight pure days, she may engage in intimacy for 15 days out of 48, as follows: seven of the first eight days are her niddah days and one is the first of her zivah days. She must watch one of her eight pure days and can engage in intimacy on the other seven. After this there are seven impure days, two of which are the last of her zivah days and six of which are among her niddah days. This is followed by eight pure days, the first of which is the end of her niddah days, and she may engage in intimacy on the other seven. This is followed by eight impure days, four of which are the last days of her zivah days and four of which are among her niddah days. She is therefore a major zavah and must count seven clean days, which are followed by eight pure days. She counts corresponding to seven days and may engage in intimacy for one day. She may therefore engage in intimacy for 15 days out of 48.