2,077. What Does the Torah Mean?

Hilchos Issurei Biah 6:16

If a woman expels semen during the days she is counting, it voids one day, like a zav for whom a seminal emission voids one day. If she saw blood on the tenth, eleventh and twelfth of her zivah days, she is not a major zavah. Rather, she goes from being a minor zavah to a niddah. The twelfth day is the start of her niddah days and a woman who sees blood in her niddah days doesn’t become a zavah, as has already been discussed.

Hilchos Issurei Biah 6:17

When the Torah says “After the time of niddah” (Leviticus 15:25), it means that if a woman saw blood on the three days that follow her niddah time, then she is a zavah. For example, let’s say that a woman saw blood on the eighth, ninth and tenth days after the start of her niddah days – i.e., the first three of her 11 zivah days. She then saw blood on her eleventh zivah day and immersed in a mikvah on the eve of the twelfth day, after which she participated in an act of intimacy. Even though she is ritually unclean and the man who was intimate with her is rendered unclean, plus the laws of impurity vis-à-vis the places where they sat and lie apply, they are nevertheless not subject to kareis (excision). This is because the twelfth day isn’t connected to the eleventh day in order to render her a zavah. Her immersion in a mikvah that night is sufficient to exempt her from having to bring an offering.