Doubtful Onset Day of Menstrual Cycle
Question
My wife noticed a stain, and after about two days her menstrual cycle began. Unfortunately, she does not remember on which day the cycle started and she has a doubt over about 4 days. Now, about a month has passed since the sighting. Are we now forbidden all the 4 doubtful days of “monthly cycle” and “average cycle” count, or can we be lenient, especially since she probably saw it during the day? What is the law on the Sabbath night which is also one in the range of doubtful days?
Answer
Shalom!
In case of a doubtful regarding the day of the menstrual cycle onset, it is permitted.
Therefore, on all the days where there is doubt if she saw blood, she is permitted.
However, if she kept bleeding for four or more days, then on the fourth day of the doubtful days, she definitely saw blood, and she needs to keep this day as the onset day of her menstrual cycle.
Source
According to Shulchan Aruch, section Yoreh Deah, chapter 184, paragraph 4.