703. Rosh Chodesh

96:15 One who forgot to make havdalah on Saturday night, or who was prevented from doing so by circumstances beyond his control, or who did not do so intentionally, may make it until the end of Tuesday. (One should not intentionally delay it that long; he should make havdalah as soon as possible. Also, one who is able to make havdalah may not eat until he does so – Mishnah Brurah 299:16.) In such case, he does not recite the bracha over the spices or over the candle, just the bracha over the wine and the bracha of havdalah itself. After Tuesday is over, one can no longer make havdalah. This is because the first three days of the week are considered days after the preceding Shabbos and are therefore relevant to that Shabbos. The next three days are considered relevant to the next Shabbos and therefore have no connection with the previous Shabbos. (The concept of three days to recite a missed havdalah only applies to Shabbos, not to yom tov. If one does not recite havdalah after yom tov, he may only do so the next day – MB ibid.)

97:1 Some have the custom to fast the day before Rosh Chodesh. (Editor’s note: Rosh Chodesh is the first day of a new Hebrew month, popularly translated as “New Moon,” though a new moon is a different event astronomically). They recite the order of prayers for Yom Kippur Katan, which atones for all the sins of the entire month. This is like the Rosh Chodesh sacrifice, as we say in the Rosh Chodesh musaf service, “a time of forgiveness for all their generations.” Each place follows its own customs in this matter. (It’s advisable, the first time one undertakes such a fast, to stipulate that he is not permanently obligating himself in the matter. If the day before Rosh Chodesh is Shabbos, those who fast push it back to Thursday – MB 417:4.)