If you recite birkat ha'mazon after se'uda shlishit over a cup of wine, you may only drink the wine if the meal ended before sunset.  

Here are the times when men and women are forbidden to get haircuts and men are forbidden to shave, including their necks (from most severe restrictions to least):
Most Severe Restrictions

• Mourner for parents (no shaving for the first 30 days and no haircut until three months after his or her previous haircut).
  Note If mourning for other relatives, you may get a haircut after 30 days.
• From Saturday night before Tish'a B'Av until the evening after Tish'a B'Av.
• Chol ha'moed.

Next Most-Severe Restrictions
Shiv'asar B'Tamuz (17^th of Tamuz) until the evening after the Shabbat preceding Tish'a B'Av.

Least-Severe Restrictions
During 33 of the 49 days of counting the omer (sefirat ha'omer); that is, either from the second day of Passover until Lag Ba'Omer (33rd day of the omer) OR from Rosh Chodesh Iyar until the day before Shavuot, according to your custom.

Introduction to Fast Days
The purpose of Jewish fast days is to make us reflect on our behavior and improve it by:

• Eliminating negative actions and thoughts, and
• Taking more care in our observance of the commandments.

God told the Jewish people on many occasions that He did not want their pointless sacrifices or fast days but rather wanted the Jews to improve their behavior. If people fast but still have reprehensible behavior, the people have missed the point and purpose of bringing sacrifices and having fast days.
All fast days may be circumvented for health reasons. Consult a rabbi.
Fast days come in several varieties:

• Major fast days: Yom Kippur and the Ninth of Av (Tish'a B'Av). 
• Minor fast days: There are four minor fast days; see below.
• Fast for First-Born
• Individual Fasts

The Major Fasts
Yom Kippur and the Ninth of Av begin before sunset and are both slightly longer than 24 hours. Yom Kippur is a festive day while, on the Ninth of Av, Jews mourn for the destruction of both Jerusalem Temples (the first was destroyed by Babylonians; the second, by the Romans). On both fasts, it is forbidden to:

• Eat or drink.
• Wear leather shoes (but you may wear any other clothing made of leather).
• Bathe (or even to wash anything more than fingers; you may not use a deodorant--not even a spray type--since it is similar to washing).
• Have marital relations.
• Use cosmetics or body scents.

The Minor Fasts
The four minor fasts begin 72 minutes before local sunrise. They technically end at dark but functionally end after ma'ariv (and for the Fast of Esther, after hearing the megila). Unlike most times in the Jewish calendar, this 72 minutes is normal time and NOT based on the current length of the day (sha'a zmanit):

• Fast of Esther (Ta'anit Esther): Day preceding Purim (or sometimes earlier).
• Fast of Gedalia (Tzom Gedalia): Usually the day after Rosh Hashana.
• Tenth of Tevet (Asara b' Tevet):
• Seventeenth of Tamuz (Shiv'asar b'Tamuz): Beginning of the Three Weeks of semi-mourning beforeTish'a b'Av.

On all fast days, eating and drinking are forbidden. The Tenth of Tevet and the Seventeenth of Tamuz additionally have the same restrictions as the Nine Days. So you may wash or bathe on the Fast of Esther and on Tzom Gedalia but not on the Tenth of Tevet and the Seventeenth of Tamuz. (See Nine Days: Restrictions).
Note On a fast day that has been delayed for Shabbat, there may be leniencies for:

• The mohel, sandak, and father of a baby getting a brit mila to eat after mincha.
• Pregnant or nursing women (this leniency applies to eating throughout the day).

Fast for First Born
Fast for first-born males 13 years old and older, on the day before Passover. This includes first-born cohanim and Levites (levi'im). The fast begins 72 normal minutes before sunrise and ends with kiddush at the seder. However, the widespread custom is to attend a siyum on the day before the first seder so that the first-born men do not need to fast on that day.
 
Personal Fasts
Fast by a groom and bride on their wedding day is an example of personal fasts. This fast begins 72 normal minutes before sunrise and ends with drinking wine under the chuppa.

 

1. What Makes a Woman a Nida

 
Introduction to What Makes a Woman a Nida
Vaginal Blood Flow
Only vaginal blood flow makes a woman nida. 
 
Nida D'Oraita
According to Torah law (d'oraita), a woman becomes a nida when she experiences a flow of uterine blood, preceded or accompanied by a hargasha. Because uterine blood flow is difficult to distinguish from the more general vaginal blood flow, we assume that a vaginal blood flow is from the uterus--unless a medical person (it could be a midwife) determines that the blood flow is not uterine.
 
Nida D'Rabanan
 
By rabbinic law (d'rabanan), a woman can become a nida even with only a qualifying stain (see below).

Hargasha
A hargasha is anything that signals that the woman's period is imminent. There are three classical hargashot, as well as possible hargashot that pertain only to an individual woman.
Note Many women today do not have hargashot.
 
Classical Hargashot
There are three classical hargashot:
1) Body Tremor
2) Petichat HaMakor
Some women, at petichat ha'makor (“opening of the uterus”), have a sensation of release similar to when one's bladder opens to urinate.
3) Zivat Davar Lach
Sensation of wet discharge that comes only with her period; this is not the wet discharge that every woman normally feels multiple times daily.
Note She does not necessarily need to feel it coming from her cervix in order for it to make her a nida.
 
Individual Hargashot
What Is an Individual Hargasha
The individual hargasha can be any physiological occurrence (pimples on her face, a bout of yawning, a bloated feeling in the belly, etc.) that correlates with a woman's getting her period within 24 hours. To become established as a hargasha, it must have happened three times in a row.
 
Note Cramps for most women may be a hargasha, since they may mean that the woman is about to have her period.
 
When a woman has a hargasha, we assume that her period has started, and she should immediately stop what she is doing and check internally with a bedika cloth. If she does a bedika as soon as possible and the cloth shows a forbidden color, or shows no discharge at all, she immediately becomes nida for at least 12 days, after which she goes to the mikva. 
Note If she had a hargasha and finds no blood and no discharge, she becomes a nida, since we assume there was blood and she just didn't find it.  If the bedika cloth shows brown, magenta, salmon, brick, amber, orange, etc., the rabbi will want to see the cloth to determine her status.
Note Most medium browns are OK.
 
What To Do If Not Sure
If she is not sure she has had a hargasha, she asks a rabbi and together they will sort out the answer.
 
 
Nida D'Rabanan
 
Stain (without Hargasha)
 
Stain Colors
A rabbi should be consulted in all matters of questionable colors of stains.  Some may seem to you to be forbidden but turn out to be permissible, and vice versa.
 
Stain Location
A stain of a color that could make a woman a nida can be on material or on the woman's body. None of the following lenient conditions apply if the woman is nida d'oraita:
   

1. Not positively attributable to another cause, AND
2. At least the size of a gris. For small, unconnected spots, she must evaluate whether, together, they equal the size of a gris (on material, the spots DO NOT get combined). If yes, she should consult a rabbi.

 
 
II. HARCHAKOT: How Do the Couple Conduct Themselves while the Wife is a Nida?
 
According to Torah law, when a woman is a nida, she and her husband are prohibited not only from having intercourse, but also (“lo tikrav”—Vayikra 18:19) from having any physical contact of a passionate or romantic nature (negiya shel chibuk v'nishuk)--those patterns of physical contact that often lead to intercourse. Since the penalty for violation is kareit, husband and wife should live separately during the nida period, but because we don't, we use “distancers” (harchakot) as reminders of distance while living together in the same home. The harchakot sensitize us to the smallest gestures of love. The couple who know that in a finite amount of time their union will not only be permitted, but even be davar sh'bekedusha--a thing of sanctity--will have the willpower to wait it out.
 
These harchakot are applied during the nida period:
                                 
III. Tahara after Nida:    

1. Wash or cleanse lower regions of the body.
2. Do an internal check/bedika: Insert a white cloth into vagina and circle it around to make sure to get every nook and cranny.
3. Moch dachuk: Insert a bedika cloth within two halachic hours of sunset and leave it in until after dark.

 

1. Bedika

 

2. White Underpants

 

3. No Hesech Da'at

A woman does not need to think about the seven clean days all of the time, but she must keep in mind, during the entire nida purification process, that she is not in an active nida state.  
Situation A woman found a stain and asked a rabbi about it. She assumed she was definitely nida.
What To Do Once she assumes that she has become a nida during that seven-day period, she must begin her count again--even once she has found out that she was not, in fact, a nida. 
Note If she asked the rabbi while not yet assuming that she was definitely a nida, she may continue her original count after the rabbi determines that she was not a nida.

• Full body cast.
• Being covered with sand.
• Being sweaty from head to toe.

• Moisturizer that covers most of her body.
• Adhesive that is left on her skin after a band-aid has been removed.
• Imperfect manicure, if she would not go to an interview like that.

         
 

• Shalom Bayit (in this case, she is not permitted see her husband until after dark Friday night).
• Dangerous Neighborhood.
• Infertility Issues (if she will miss ovulation if she does not go Friday night).

    Kosher immersion/tevila requires simultaneous immersion of every exposed part of the body (not bet ha'starim).   Here is the best way to accomplish simultaneous immersion:

• Enter the water until it is about 12 inches above the navel. 
• Make sure that every part of your body is relaxed (if you squeeze anything, you create crevices and cracks that impede complete access to your skin). 
• “Flesh”/basar is exposed to the water when standing while leaning a little forward.
• Exhale and push yourself under the water until you are certain that all of your body and all of your hair are submerged. 
• Once your head is above the surface of the water, say the blessing and then immerse again, the same way.

 
IV. Anticipating the Next Period/Veset
 
What To Anticipate
In anticipating the time of the month when her period is most likely to occur (onat ha'veset), a woman must determine both:

1. The day of the month, and
2. Whether it will begin during the daytime period (sunrise to sunset) or the nighttime period (from sunset to sunrise)

 
Regular and Irregular
Every woman needs to be able to anticipate her next period, whether she is a) regular or b) irregular. “Regular” is determined by any pattern to one's menstrual cycle that occurs three times in a row.
Note It is very uncommon for a woman to maintain her regular period for a long time.
 
Anticipating a Regular Period
Here are the five most classic regular patterns:

1. Veset HaChodesh (Monthly Cycle)

   

2. Veset Haflaga (Intervals Cycle)

 

3. Veset HaGuf (Body Symptoms Cycle)

 

4. Veset HaMurkav (Combination Cycle)

    A woman with an irregular period may have to abstain from relations and affectionate intimate contact (negiya shel chibuk v'nishuk) during these three onot/time periods:

1. Yom HaChodesh

 

2. Haflaga

 

3. Ona Beinonit