Haidh is a type of blood that is discharged from the womb of a woman every month. In order to better understand haidh let us follow the eight simple steps below:

Verification
If the blood seen is other than what is stated below, then it is haidh.
If the blood is not of istihadha
If the blood is not of nifas (blood seen after childbirth)
If the blood is not from a boil or surgery

Signs
Blood seen at the time of haidh usually has its own distinctive features:
It is red color or darker, sometimes even black
It is thick
It is warm
It gushes out with force and is accompanied with burning
Ensuring it is Haidh
In order to ensure that the blood seen falls into the category of haidh, the following conditions must be met:
The blood seen is not less than 3 days
The blood is seen for 3 days in a row
Continuous flow of blood for 3 days
In the beginning of the cycle (in some cases) blood is visible, later exists internally (for a few days in the vagina) and after some time it starts flowing again.
The total duration of haidh is not more than 10 days
The blood is seen by a woman who is older than 9 years according to the lunar calendar (approximately 8 ½ years solar calendar)
The blood is seen by a woman before she goes through menopause*
Between 2 cycles of menstruation, there should be at least a 10-day gap.
Note: Sayyid (Women from the progeny of the Prophet) may get their periods till the age of 60 as per the lunar calendar. Non Sayyid may get periods until the age of 50 as per the lunar calendar, as per Islamic Laws.

Categories of women
According to the rules of haidh women can be classified into six categories:
Women who have a habit of time and duration: This is a woman who sees blood at a particular date and for a fixed duration, two months in a row.
For example: A woman sees blood on the 10th of March to the 17th of March and then she sees blood on 10th of April to the 17th of April. In this case she can be classified under the category of a ‘woman with a habit of time and duration’.
Women who have a habit of duration: When a woman sees blood on different dates but the duration of the flow is the same. This happens two months in a row.
For example: A woman sees blood on the 10th of March to the 17th of March and then she sees blood on the 12th of April to the 19th of April. In this case she can be classified under the category of ‘Women who have the habit of duration’.
Women who have a habit of time: When a woman sees blood at a particular date but the duration of the discharge varies. This happens two months in a row.
For example: A woman sees blood on the 10th of March to the 17th of March and then she sees blood on 10th of April to the 18th of April. In this case she can be classified under the category of ‘Women who have a habit of time.’
Please Note: In the above examples and in other parts of the book, the Gregorian calendar has been used, as it is more familiar to the western reader. The calculations for women who have a habit of time though, require the date of the Islamic lunar calendar to be consistent.
Mudhtaribah: Disordered duration: When a woman sees blood on different dates and has no fixed duration at all.
Mubtadiyah: Beginner: One who saw blood for the first time.
Nasiyah: Forgetful: When a woman forgets her habit, which means that she has forgotten the dates and the duration.
Important Question: When a woman sees blood for 10 days, it is all considered haidh (Menses), but if she sees blood for more than 10 days, then what?
If blood is seen for more than 10 days, then she must decide which category (categories of women) she fits in and follow the rules from the ‘Rules for a woman in menses’ that follow: -

Rules for a Woman in Menses
Woman having the habit of time and duration: As was mentioned earlier this is a woman who in the last 2 months has seen blood on a particular date and for a fixed duration. When a woman under this category sees blood for 10 days then it is all haidh, but if she sees it for more than 10 days then the blood seen during the days of habit is considered part of her period and the rest is istihadha.
Some scenarios of women having a ‘Habit of Time and Duration’
Scenario 1: If a woman in the last 2 months has seen blood for 7 days but this month she sees blood for 10 days, what is her duty? In this situation she should consider all 10 days as ‘haidh’. As the flow was not more than 10 days.
Scenario 2: If a woman in the last 2 months has seen blood for 8 days (Her habit is 8 days), but this month she sees blood for 13 days, what is her duty? In this situation she should consider the first 8 days as ‘haidh’ and the 5 extra days as ‘istihadha’, because the total flow was more than 10 days. When a woman’s menses continues for more than 10 days then the blood seen during the days of her habit is haidh and the rest is istihadha.
Scenario 3: If a woman in the last 2 months has seen blood between the 10th and 18th BUT this month she saw blood from 7th to 20th, what is her duty? In this situation she should do the following:
7th to 9th……….. is istihadha
10th to 18th ….is haidh
19th to 20th ….is istihadha
Scenario 4: If a woman in the last two months has seen blood between the 10th and 18th BUT this month she saw blood between the 10th and 20th, then what is her duty? In this situation all 10 days is ‘haidh’, because the flow does not exceed 10 days. This scenario is just like scenario 1.

Woman having the habit of duration: As was mentioned earlier this is a woman who has seen blood for a fixed duration but not for a fixed time (date wise) in the past 2 months. When a woman under this category sees blood for 10 days (and it has all the signs of haidh) then it is all haidh, but if she sees it for more than 10 days then blood seen during the days of habit of duration is period and the rest is istihadha.
Some scenarios of women who have a ‘Habit of Duration’
Scenario 1: If a woman in the last two months has seen blood for 8 days BUT this month she sees it for 13 days, what is her duty? In this situation she should consider first 8 days as ‘haidh’ and the rest as ‘istihadha’, because she had a habit of 8 days and this month the flow was more than 10 days.
Scenario 2: If a woman in the last 2 months has seen blood for 8 days BUT this month she sees it for 10 days, what is her duty?
In this situation she should consider all 10 days as ‘haidh’, as the flow was not more than 10 days.
Woman who have a habit of time: As was mentioned earlier this is a woman who has seen blood on a particular date in the past 2 months but has no fixed duration. When a woman under this category sees blood for 10 days (and it has all the signs of haidh) then it is all haidh, but if she sees blood for more than 10 days then she must follow the guidelines below:
If the blood seen has signs of haidh then the number of days it has the signs of haidh is ‘haidh’, the rest is istihadha. (If the blood has the signs of haidh and the same signs remain for 13 days, then it is as if there were no signs)
If the blood has no signs of haidh, and the only way the woman knows it is haidh is because of her habit of time, then she should consult her family, to verify the normal time duration of period experienced by female members of her family. If the majority of the women in her family have similar durations, she should follow their pattern. In this case the normal duration in the family is considered to be haidh, and the remaining days is istihadha.
If the family members have different durations and it is hard to determine, then a woman must calculate the first 7 days as part of her menses, and the rest as istihadha.
Note: consulting your family for the number of days means to ask your mother, sisters, paternal aunts and maternal aunts, and grandmothers about their blood cycle (menstruation). Asking about their duration, means to ask how many days do they see blood every month?

Some scenarios of women who have a ‘Habit of Time’

Scenario 1: This woman since the last 2 months has seen blood on one particular date but her duration varied. This month she saw blood on the same date but the flow went on for 10 days. In this situation all the ten days are considered to be ‘haidh’.
Scenario 2: This woman since the last 2 months has seen blood on one particular date but her duration varied. This month she saw blood on the same date but the flow continued for 13 days. If the blood had all the signs of haidh for 8 days for example, then this woman should consider 8 days as being haidh and the rest as istihadha.
Scenario 3: This woman since the last 2 months has seen blood on one particular date but her duration varied. This month she saw blood on the same date but the flow carried on for 13 days. There were no signs of haidh. In this situation this woman should consult her family and if for example her family has a habit of 8 days then this woman should consider 8 days as being haidh and 5 days as istihadha.
Scenario 4: This woman since the last 2 months has seen blood on one particular date but her duration varied. This month she saw blood on the same date but the flow carried on for 13 days. There were no signs of haidh. In this situation this woman should consult her family and if her family has no particular duration, then she should consider 7 days to be haidh and the rest istihadha.
Scenario 5: This woman since the last 2 months has seen blood on one particular date but her duration varied. This month she saw blood on the same date but the flow carried on for 13 days. There were no signs of haidh. In this situation this woman should consult her family BUT if she has no family, then she should consider 7 days as haidh and the rest istihadha.

Mudhtaribah: Disordered duration:
As we mentioned earlier, in the past 2 months when a woman sees blood on different dates and has no fixed duration at all then she is known as Mudhtaribah. If she sees blood for more than 10 days then she must follow the guidelines below:
If the blood has signs of haidh, then the number of days with signs is haidh and the rest is istihadha. (If the blood has the signs of haidh and the same signs remain for 13 days, then it is as if there were no signs).
If the blood has no signs of haidh then the way to calculate the duration is:
A woman should consult her family, to verify the normal time duration of period in the family. Once she has a number. Then she should…
Use the number 7 to calculate the # of days of haidh and the # of days of ‘Jum`*’ and the # of days of istihadha. (This will be more clear when we get into different scenarios)

Jum`*: Jum` means following the rules of both haidh and istihadha at the same time. In the days of Jum`, a woman cannot do the things that are haram in haidh, but must do all the things that are wajib (obligatory) in istihadha. Since salat is obligatory in istihadha along with ghusl (ritual bath) she must perform ghusl and salat. Since sex is haram (prohibited) in haidh then she should refrain from sex.
Some scenarios of Mudhtariba: Disordered Duration
Scenario 1: This woman in the past 2 months has seen blood on different dates and the blood flow did not have a fixed duration. She saw blood for 13 days and out of those 13 days there were 8 days where she saw signs of haidh. In this situation she should consider 8 days as haidh and the rest as istihadha.
Scenario 2: This woman in the past 2 months has seen blood on different dates and the blood flow did not have a fixed duration. Then this month she saw blood for 13 days, and the blood had no signs of haidh. In this situation she must consult her family, to verify the normal time duration of ‘haidh’ in the family. Let us suppose the number of days that make up the normal duration of haidh in her family is 5 days. Since 5 days is less than 7 (the number 7 is what we discussed in ‘B’ above), she should follow these guidelines:
The duration of her haidh is 5 days
The duration of ‘Jum`” is 2 days (Difference between 5 and 7)
The duration of istihadha is 6 days
Total duration of blood flow is 13 days

Scenario 3: This woman in the past 2 months has seen blood on different dates and the blood flow did not have a fixed duration. This month she saw blood for 13 days. The blood had no signs. In this situation she must consult her family, to verify the normal time duration of ‘haidh’ in the family. Let us suppose the number of days that is the normal duration of haidh in her family is 8 days. Since 8 days is greater than 7 (the number 7 is what we discussed in ‘B’ above), she should follow these guidelines:

The duration of her haidh is 7 days
The duration of ‘Jum`” is 1 days (Difference between 7 and 8)
The duration of istihadha is 5 days
Total duration of blood flow 13 days
Scenario 4: This woman in the past 2 months has seen blood on different dates and the blood flow did not have a fixed duration. This month she saw blood for 13 days. The blood had no signs. In this situation she must consult her family, to verify the normal time duration of ‘haidh’ in the family. Let us suppose the number of days that is the normal duration of haidh in her family is 7 days. Since 7 days is the same as 7 (the number 7 is what we discussed in ‘B’ above), she should follow these guidelines:
The duration of her haidh is 7 days
The duration of ‘Jum`” is 0 days
The duration of istihadha is 6 days
Total duration of blood flow 13 days
Mubtadiyah: Beginner : This is a woman who sees blood for the first time. Then she is known as “Mubtadiyah’. If she sees blood for more than 10 days then she should follow the same rules as a woman ‘having the habit of time’ does.
If the blood seen has signs of haidh, the number of days it has the signs of haidh is ‘haidh’, and the rest is istihadha. (If the blood has the signs of haidh and the same signs remain for 13 days, then it is as if there were no signs).
If the blood has no signs of haidh, then a woman should consult her family, to verify the normal time duration of haidh in the family. If the majority of women in her family have the same number of days, she should follow their pattern. Then the normal duration in the family is going to be haidh, and the remaining days is istihadha.
If the family members have different durations and it is hard to determine, then she must calculate according to a 7-day period, the rest being istihadha.
Note: Consulting your family for the # of days means asking your mother, sisters, paternal aunts and maternal aunts, and grandmothers about their blood cycle (menstruation). Asking about their duration, means asking how many days do they see blood every month?
Some scenarios of Mubtadiya: Beginner
Scenario 1: This woman has seen blood for the first time. The blood flow went on for 10 days. In this situation, all the ten days are ‘haidh’.
Scenario 2: This woman has seen blood for the first time. The blood flow carried on for 13 days. If the blood had all the signs of haidh for 8 days for example, but did not have the signs of haidh for the last 5 days, then this woman should consider 8 days of haidh and the rest Istihadha.

Scenario 3: This woman has seen blood for the first time. The blood flow carried on for 13 days. There were no signs of haidh. In this situation this woman should consult her family and if for example her family has a habit of 8 days then this woman should consider 8 days as being haidh and 5 days as istihadha.

Scenario 4: This woman has seen blood for the first time. The blood flow carried on for 13 days. There were no signs of haidh. In this situation this woman should consult her family and if her family has no particular duration, then she should consider 7 days as haidh and the rest as Istihadha.

Scenario 5: This woman has seen blood for the first time. The blood flow carried on for 13 days. There were no signs of haidh. In this situation this woman should consult her family BUT she has no family, then she should consider 7 days as haidh and the rest as istihadha.

Forgetful: Nasiyah: When a woman forgets her dates and duration she is known as ‘nasiyah’. If she sees blood for more than 10 days then she should follow these guidelines:
If the blood has signs of ‘haidh’ and it lasts no more than 10 days then it is all considered ‘haidh’.
If blood has signs of ‘haidh’ for 8 days, no signs for 5 days, and the blood flow lasts 13 days, then 8 days is haidh and 5 days is istihadha.
If blood has no signs at all and the flow lasts 13 days, then she should consider 7 days as ‘haidh’ and the remaining days as ‘istihadha’.
Different Types of Menstruation
Type 1: This woman is clean the whole month, only sees blood during the days of menstruation.
Type 2: This woman sees blood (spotting) the whole month, but during the days of haidh the blood has signs of haidh.
Type 3: This woman is clean the whole month, but during the days of haidh, she sees blood for a couple of days, then there is no blood for a day or two, then she sees blood again. If this routine continues for 10 days then it is all haidh. This is as per Imam Khomeini.
Note: As per Ayatullah Seestani the days within the period of haidh when one does not see blood should be considered as ‘Jum` ‘, Ihtiyat-e-Wajib, (please refer glossary for the meaning of jum` and Ihtiyat-e-Wajib).

Qadha Salat
Performing salat is haram while a woman is in haidh, but as soon as she feels that she is done with haidh then she should pray within the time for salat. Below are some problem scenarios and some solutions:
This woman was clean and delayed salat and then got ‘haidh’. This woman needs to do Qadha for this Salat when she is done with haidh,
As she did not pray on time that day and she delayed when she could have prayed on time.
This woman had her period and when it stopped, she had just enough time to take the ritual bath and do wudhu and pray. She delayed it, hence the time for Salat passed. She must do Qadha Salat, because she had enough time to take the ritual bath, wudhu and pray but she did not.
This woman was clean then she saw blood, so she thought it was haidh. Then later she realized that it was not haidh. She should do Qadha prayers for all the prayers she missed.
Things that are Haram (prohibited) in ‘Haidh’ (Menses):
Worship for which wudhu is required, for example: Salat, Fasting, and Tawaaf of Ka’aba.

Sex.
All the actions that are haram in the state of janabat:
It’s Haraam to enter Masjid ul Haram and Masjid un Nabi.
Stopping in other mosques and the shrines of Imams is Haraam. Passing through one door and coming out through another door is okay as long as one does not stop in a Masjid or Shrine of Imams.
Placing something in the mosque is Haraam, but picking up something is no problem, according to Imam Khomeini. However as per Ayatullah Seestani a woman cannot place something or pick up something while a woman is Junub or when in the state of Haidh.
Reciting 4 surahs that contain the Wajib Sajda is Haram: Surah Sajda, Surah Fussilat, Surah Al-Najm and Surah Al-Alaq. According to Imam Khomeini, even reciting one word of the surahs mentioned above in the state of janabat or haidh is haram.

Note: Ayatullah Seestani says that reciting the Surah is not a problem but a woman in the state of haidh or janabat should not recite the ayats that have the Sajda e wajib in them. Surah Sajda Ayat 15, Surah Fussilat Ayat 38, Surah Al-Najm Ayat 62, and Surah Al-Alaq Ayat 19.
It’s haraam to touch the words of Qur’an with any part of the body.
It’s haraam to touch the names of Allah in any language.
It’s Haraam to touch names of Prophets and Imams and Syeda Fatema (SA). as per Imam Khomeini its Ihtiyat-e-Wajib not to touch the names of the 14 infallibles.

Note: As per Ayatullah Seestani its better if a woman does not touch the names of the 14 Infallibles in the state of janabat and haidh.
Miscellaneous Points regarding Haidh
A pregnant or a breast-feeding woman may also see haidh. Depending on the signs of the blood, if a woman is certain that the blood is haidh (please refer to point #3 in the section of haidh for ways to be certain), then she should follow the rules of haidh.