2,102. Seeing Blood for 9-13 Days

Hilchos Issurei Biah 8:19

If the woman saw blood for nine days, there’s a doubt as to whether or not she’s a zavah; maybe two of the days preceded her niddah days and the other seven are her niddah days. She therefore starts counting her eleven (zivah) days after the ninth day, when she stops seeing blood. The same is true if she sees blood for eleven days: there’s a doubt whether or not she’s a zavah because maybe two of the days preceded her niddah days, seven are her niddah days and two followed her niddah days. There would therefore be nine days left in her zivah days.

Hilchos Issurei Biah 8:20

If the woman saw blood for 12 days, she is definitely a zavah because even if two of the days preceded her niddah days and seven were her niddah days, there were still three days that followed her niddah days. There are therefore eight days left in her zivah days. The same is true if she saw blood for 13 days: there are seven days left in her zivah days, which are counted as her seven clean days.