Menstruation table: how does it work? Learn to calculate!

The menstruation table can be used as a way to control the menstrual cycle and many women also use it as a contraceptive method.

It is more likely to work on regular cycles, but it is still not very effective in preventing pregnancy. For irregular cycles, it is recommended to calculate the average of the last six months to try to understand how it works.

Remember that ready-made tables are made based on a standard menstrual cycle of 28 days, however, it can vary between 21 to 40 days. Therefore, each woman should make her table based on the length of her cycle.

The table method is not enough to prevent pregnancy. The ideal is to combine it with other contraceptives.


How the menstrual table and fertile period works

The menstrual table is used to calculate the beginning and the end of the menstrual cycle and to know the fertile period .

Here are some tips to start making your table. To do this, you will need the following information:

  • When did your last period start?
  • How many days did it last?
  • How long is your menstrual cycle?

If you do not know any of the information, you will need to write down the start and end dates of each period for at least six months, so that the table is as accurate as possible.

After this period, it is already possible to start using it to have more control of the menstrual cycle.

How to assemble the table

This method works best for those who have their periods regulated, with the same interval of days in all cycles.

However, it is also possible to be used by women who do not have the same frequency, however, being even less safe.

The menstrual cycle begins on the 1st day of menstruation and lasts until the eve of the next menstruation, that is, the next bleeding.

For the table, it is important not to confuse the days of the month with the days of the menstrual cycle.

Despite the standard being 28 days, most women have different duration cycles.


The first day of menstruation (bleeding) is marked on the table until the last day, which will identify the menstrual period.

Menstruation is nothing more than the flaking of the endometrium, identified by menstrual bleeding. It can last, on average, between 2 and 8 days.

Fertile period

The fertile period happens about 14 days before the next menstruation. In this phase, hormonal changes occur that stimulate the ovary to release an egg that will go to the fallopian tubes.

End of cycle

At the end of the cycle, if the woman becomes pregnant, the egg will go to the uterus and stick to its inner layer.

And if she does not become pregnant, the inner layer of the uterus (endometrium) will undergo desquamation and will be expelled through the vaginal opening, thus starting a new menstrual cycle.

Check below an example of how the table of a 28-day menstrual cycle looks (the most common among women) with the appropriate markings:

  • 1st to 5th day: menstruation occurs, the so-called infertile period;
  • 6th to 10th day: infertile period;
  • 11th to 16th day: fertile period, probably 14th is the most fertile;
  • 17th to 28th day: infertile period, as the egg period has passed and the woman’s body is getting ready for the next menstruation.

Identifying the fertile period

The fertile period is the length of time within the menstrual cycle in which the woman is most likely to become pregnant, which is on the day of ovulation and the day before.

In a 28-day menstrual cycle, ovulation occurs around the 14th day, in the middle of the cycle. The most fertile days include the 3 before and 3 after the day of ovulation, that is, between the 10th and 19th day of the cycle.

Always remembering that the tablet, as it is popularly known, is not a safe method of contraception precisely because it is difficult to predict changes in the cycle.

Although the most fertile days are ovulation and the previous 3, according to Clearblue, there is a chance of getting pregnant in the days before ovulation.

Below is an estimate of this probability *:

Day related to ovulationProbability of getting pregnant (%)
6 days before0%
5 days before10%
4 days before16%
3 days before14%
2 days before27%
1 day before31%
Ovulation Day33%
1 day after ovulation0%*

* Percentages are only estimates based on regular, unchanged cycles. It is worth remembering that changes can occur in the organism that affect ovulation. Therefore, although rare, it is also possible to get pregnant during menstruation.

How is the menstruation table made to avoid getting pregnant?

To make the table, it is necessary to write down the days of your menstruation in a calendar, so that it is possible to identify the fertile period, in which you should avoid having intercourse or prevent yourself from becoming pregnant.

If you have a 28-day menstrual cycle, mark your first menstrual day on the calendar and count 14 days to identify that period.

The menstrual table is not considered a safe method to prevent pregnancy, as the chances of going wrong are high. Several factors can alter the date of menstruation, such as strong emotions, stress and the use of medications.

Because of this, the date of ovulation is not well defined, which makes the table unsafe.

Menstruation and ovulation table

Ovulation happens in the middle of the menstrual cycle and is the peak moment of fertility. For those who have irregular cycles, it is not usually easy to calculate the day of ovulation.

At this stage, estrogen levels increase, also causing an increase in luteinizing hormone, which is responsible for selecting the most mature egg to expel from the ovary.

As soon as the egg is released, it travels through the tubes and reaches the uterus. In general, it survives for up to 24 hours outside the ovary. The sperm remains alive for up to 5 days inside the woman’s body.

Women who use contraceptives in general do not ovulate and therefore do not become pregnant.

Knowing your menstrual cycle is a form of self-knowledge that allows you to understand the functioning of the body and to respect the changes that occur in each phase of the cycle.

That way, it is possible to predict the days when you will be menstruating or in the fertile period, to be able to plan trips and appointments or to avoid or plan a pregnancy.

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