Many people have not gone through an in_depth study of the laws of Niddah. Nevertheless, with even a basic understanding of these laws, a woman can make very far_reaching determinations concerning her Niddah status. Since our Rabbis have instituted many safeguards the chances are slim that even an imprecise determination would lead to a violation of a Torah law.
Although in many cases any woman can decide about her own blood, a rabbi should be consulted as needed. The rabbi will occasionally make a more lenient determination than the woman might have, having a fuller and more thorough understanding of the halacha including its rabbinic safeguards. Additionally, after referring her questions to the rabbi on numerous occasions the woman will herself gain a fuller understanding of the halachic issues involved, and will herself become better able to make more complicated determinations.
1. According to the Torah women are believed with regard to everything concerning their Niddah status. This includes the determination whether she is not niddah or is niddah due to a stain etc.
2. The woman's credibility is not questioned, unless it happened that the woman was niddah and claimed falsely to have had immersed. In that case she is never again believed until it is clear that she has completely repented from this grave offense.
3. A man cannot have marital relations with his wife if he knows she was niddah until she indicates that she has properly immersed. Amorous intimations on the night of her supposed immersion are enough of a hint by the wife that she has immersed. This applies even if there is a blood stain on her clothing since it might be due to her involvement with meat or other staining substances.
4. If a woman said to her husband that she is niddah and subsequently said that she is really not niddah she is considered niddah, unless she gives a good reason for her earlier niddah pronouncement. If she does not give a good reason she must do a hefsek betahara, count seven clean days and immerse. This immersion should be without a prior blessing since she knows that she was really not niddah. Examples of "good reasons" are: she claims to have felt weak and could not stand having relations; that her parents were in close proximity; that she had a stain which proved to be pure; or anything of the like.
5. If the couple had an argument during which the wife claimed to be Niddah, they may have relations if she comes to lay with him. The husband should understand that she claimed to be Niddah because of the argument.
6. This applies even at the time when she is expecting her period (see chapter discussing separating at the time a period is expected and the chapter on how these times are figured)
7. If a woman claimed as her excuse that she was "only joking" she is considered niddah, however, if she is known to play such practical jokes, she is not considered niddah. This type of joking is unbecoming to the woman and she should desist from it in the future. If she gave an otherwise unlikely reason for her claiming to be niddah the rabbi should be consulted.
8. If a woman said that she is niddah and immediately retracted and said that she is really not niddah, she is believed and is not considered niddah. 12
9. The above rules also apply to a woman who had immersed and claimed that she hasn't.
10. If a woman had a stain and she claims that a knowledgeable person told her that it does not affect her status, she is believed. However, if the authority was questioned and did not corroborate her story, saying either that she never asked him or that he had determined her to be niddah, he is believed and she is considered niddah.
11. If a woman claims that a knowledgeable person told her that marital relations are permitted and another individual claims that the authority said that she is really Niddah, the woman is believed.
12. There are additional rules on this subject and the rabbi should be consulted if there are doubts.