How to Calculate Fertile Period (Regular and Irregular) and Symptoms

Whether for women who want to get pregnant or for those who want to prevent pregnancy, getting to know their own bodies and knowing about the menstrual cycle is very important.

Although there are several changes throughout the month, the menstrual cycle has no secret.


What is fertile period?

The most fertile period, popularly known as the fertile period, is when the woman is ovulating, so she is more likely to become pregnant. It occurs on average 14 days before menstruation and has a durability of 6 to 7 days.

The method of calculating the fertile period, (popularly called tabelinha) is extremely useful for those who want to get pregnant, the famous tentants, because the chances of getting pregnant during the fertile period are much greater, because the eggs are ripe and are released for fertilization. .

Fertile period to get pregnant

For women looking for a pregnancy, the fertile period is the ideal time to try a conception. Consult your gynecologist to guide you through the beautiful process of planning a new life.

Unlike men who produce sperm throughout their lives, women are born with their eggs counted: there are about 450,000! They are stored until they mature and are usually only released one at a time during the cycle.

To get pregnant, it is necessary that your health and that of your partner are up to date. Remember that only the woman will not do the whole process alone, so it is necessary that the partner is as healthy as the woman.

Studies show that semen quality is highest when there is a 2 to 3 day interval between ejaculations, so if you are trying every day and nothing so far, this can be a good indication of where you are doing it wrong.

During the fertile period, at least 3 sexual intercourse with quality semen must be guaranteed.

Do not believe the myths that say “X” or “Y” position will facilitate or hinder pregnancy: the position or orgasm has no influence on fertilization.

However, the use of some lubricants like KY and Astroglide can inhibit the ability of sperm to move, that is, it makes it difficult for them to swim to the egg, so couples wishing to become pregnant should avoid them as much as possible.

Read more: How do I know if I’m ovulating? Tips and calculator to get pregnant

Menstrual cycle

It is impossible to understand the fertile period without first understanding the menstrual cycle and how it affects female fertility.

Menstruation starts in adolescence and lasts until menopause , it represents the woman’s fertile years. Usually composed of 28 days, this cycle is divided into 3 phases, which vary according to the hormonal changes suffered in the female organism.

If your cycle does not have 28 days, stay calm! This does not mean you are an aberration: it is normal for cycles to vary from 25 to 35 days, sometimes up to 38. However, cycles with very short or very long intervals can pose problems like polycystic ovaries . If this is the case, consult a gynecologist as soon as possible.

As already mentioned, the menstrual cycle has 3 phases. Are they:

Follicular phase

Begun on the first day of menstruation, the follicular phase lasts from 5 to 12 days. At this stage, the brain is stimulated to produce more follicle-stimulating hormones (FSH), responsible for stimulating the ovaries to mature the eggs.

As the eggs mature, the ovaries increase the release of estrogen, the hormone responsible for making the lining of the uterus conducive to pregnancy.

Ovulatory phase

The ovulatory phase is like choosing fruits. Estrogen levels rise so much that the body begins to produce luteinizing hormone (LH). This hormone selects the most mature egg and causes it to leave the ovary, thus ovulation, usually around the fourteenth day of the menstrual cycle.

Once harvested, the egg begins its way to the uterus, passing through the tubes. Outside the ovary, the egg needs certain hormones to survive.

However, such hormones are found only in the ovary, so the egg can only stay alive for twenty-four hours after its release. Here is the need for the sperm to contact it quickly.

It is not unexpected that fertilization occurs on the first day of ovulation, as sperm survive up to five days inside the female body.

In short, just like a ripe fruit, the egg needs to be harvested. Otherwise, it becomes useless.

Luteal phase

Last, but not least, the luteal phase occurs in the last twelve days of the cycle. In this period, the follicle that was left by the egg inside the ovary starts the production of progesterone at high levels, as it continues to prepare the body for a possible pregnancy.

Another hormone that is present is estrogen, which, among other functions, increases breast tissue, uterus and vagina, causing many women to experience changes in mood and tenderness in the breasts.

If fertilization does not occur, the follicle gradually shrinks, just as the hormones cease to act in favor of a possible pregnancy. The levels of estrogen and progesterone decrease until the lining of the uterus begins to loosen, that is, until the start of menstruation.

However, if there is fertilization, the egg will stick to the uterine walls and the body will start producing human Chorionic Gonadotropin (hCG), popularly known as the pregnancy hormone.

At this stage, hCG is responsible for keeping the progesterone and estrogen-producing follicle high, because only then will the uterus maintain its lining until the placenta forms.

Types of menstrual cilo

There are two types of fertile periods:


Lucky are the women who have the regular ovulation period! This type of period is characterized by the beginning being 14 days before menstruation, in an ideal cycle of 28 days.

In these cases, the fertile period lasts approximately 6 days, with the first two days of intense activity in the body.


A woman may have a regular and irregular fertile period throughout her life, or just one of them. This is because irregular fertile periods are triggered for some reason. The main ones are:

  • Stress;
  • Tiredness;
  • Excessive physical activity;
  • Large and rapid changes in weight;
  • Poor diet (excess of caffeine or alcohol);
  • Hormonal changes (caused by birth control pills, antidepressants, polycystic ovary syndrome or fibroids).

Symptoms in the fertile period


Many women don’t even know how to spot the signs of the fertile period, so check out the most common symptoms below.


It is not just the hormones estrogen and progesterone that enter the hormonal party that the female body becomes with the fertile period. Also included is testosterone, a hormone that helps increase sexual desire and increases the production of sebaceous glands.

Such glands are microscopic, are located on the skin and secrete sebum, responsible for the appearance of pimples and blackheads during this period.

Vaginal mucus

Vaginal secretion, or simply vaginal mucus, varies during the menstrual cycle. The mucus that characterizes the most fertile period has an egg white aspect: it is highly slippery and can be stretched from five to eight centimeters without breaking.

These characteristics allow sperm to swim easily to the cervix.

Another type of vaginal mucus that indicates fertility is watery. Cervical discharge becomes wetter when ovulation is close to occurring.

Slightly elevated body temperature

Remember that follicle you mentioned above, which increases progesterone? It is the cause of the high temperature! It turns out that progesterone is also responsible for regulating the temperature, so when the follicle encourages its increase, it ends up influencing body temperature.

For the benefit of all women, the increase is not that significant and represents 0.3 ° to 0.8 ° C.

Pains in the lower abdomen

Many women went through this symptom and did not even associate it with the fertile period, which is not surprising, as it is completely unconscious. Normally, pelvic pain arises on one side at a time and with days apart, the motivation is to release the egg.

This process varies from organism to organism, and can be slightly painful for some women and completely painless for others. In some cases, it happens that the woman has pain in one period and in the other she does not.

Increased libido and appetite

If you haven’t tired of hearing about them, here we go! One more symptom and, again, the culprits are hormones. Throughout the month, female hormones are always changing, unlike men who have them more consistently.

During the fertile period, the hormone responsible for sexual desire, testosterone, appears in greater concentration in the female organism, causing the woman’s sexual appetite to become more intense. In other words, it is the organism dictating that it is the ideal time to perform sexual activity, as it is more conducive to generating new life.

The appetite increases, due to the pleasure that the body feels when eating, this symptom is also related to the instinct to store energy and nutrients provided by food.

Emotional instability

Hormonal changes affect emotions directly, and can make a woman irritable or tearful from one moment to the next.

Other symptoms

In some women, there are other symptoms, which appear more rarely and vary from case to case. Among them, the most reported are:

  • Swollen and / or painful breasts;
  • Feeling of heaviness in the breasts;
  • Weight gain;
  • Migraine;
  • Nausea.

How to calculate the fertile period?


Calculating the fertile period is easier than it looks, but you have to be extremely patient and cautious in your calculations. Separate paper and mug and follow these three steps:

First step: check your cycle size

To check the size of your menstrual cycle, it is necessary to analyze the latest dates when menstruation occurred. Through the extension of the cycle, the most likely day of ovulation is determined and, as a result, the calculation of fertile days.

For example: if Ana menstruated on October 30th and the next menstrual period arrived on November 24th, then Ana has a 25-day cycle. That’s because, from the 30th to the 23rd, it had an interval of 25 days. The 24th day is not counted because the menstrual cycle is counted from the first day of menstruation to the day before the next menstruation.

However, a fertile period cannot be affirmed by just one cycle. It takes at least 6 months of cycles to determine a count, since the size of the cycle can change and, if applicable, the cycle will be irregular and will require a specific count.

Second step: determine the likely date of ovulation

Now that you have the size of your menstrual cycle, let’s find out how to calculate your likely ovulation date.

Our friend ovulation should normally give faces from twelve to sixteen days before the end of the cycle. On average, ovulation occurs fourteen days before the cycle ends, so to determine the probable date we must subtract fourteen days from the total size of the cycle.

Size of your menstrual cycle – 14 = Day of the cycle on which ovulation is most likely to occur

If we use our friend Ana, who has a regular cycle of 25 days, then the calculation will be like this:

25-14 = 11

This means that the eleventh day of the menstrual cycle is the most likely ovulation to occur. That is, Ana would be ovulating on November 9.

Third step: calculate the fertile days

The most fertile days are the five days leading up and the day after ovulation. For this reason, one more calculation will be necessary. It is not difficult, so relax that we are almost there!

Now that we have the calculation of the day of ovulation, it will be necessary to determine the first day of your fertile period. If ovulation will occur on the eleventh day, then we have to subtract 5 days to determine the first fertile day. Again, we’ll use Ana’s example. Follow the calculation:

11 (day of ovulation) –  5 (days before ovulation)  = 6 (first fertile day of the cycle)

In short, Ana’s first fertile day will be the 6th day of her cycle and will continue until the next day of ovulation, that is, until the 12th day of her cycle.

It is necessary to add 2 days for the error margin, since the 14th day is just the average, when ovulation can occur from 12 to 16 days before the end of the menstrual cycle.

If you are trying to conceive, know that the method of calculating the fertile period, also called a table, is not 100% reliable and, statistically speaking, does not work with all women. For more assertive results, use ovulation tests.

Ovulation tests

Ovulation tests work in the same way as strip pharmacy tests, which detect a hormone from urine. In this case, the hormone to be identified is luteinizing (LH). If your presence is confirmed, the strip will show two stripes, confirming fertility.

How to calculate the irregular fertile period?


Calculating the irregular fertile period requires even more patience than the regular one. As in the case of regular cycles, as exemplified above, it is extremely important to consider the count of the last six months of cycles.

As taught in the first stage of the regular cycle, it is necessary to calculate your cycles. In the case of irregularities, you must select the smallest and the largest cycle. In such cases, the fertile period is considered when the woman is between the first day of the fertile period of the minor cycle and the last day of the fertile period of the major cycle.

Let’s use Ana’s friend, Eduarda, to exemplify the irregular cycles. Eduarda had cycles between 27 and 32 days in length, so she will do the second and third step above and will find the first day of the shorter fertile period, which is the twenty-seven day period. Watch:

27 (Shortest cycle) – 14 = 13

This means that when Eduarda has a cycle of 27 days, ovulation will occur on the 13th day of the cycle.

To obtain the first day of the fertile period, we will subtract 5, just as we did in Ana’s third stage.

13 ° (Cycle day) – 5 days = 8 ° cycle day

See that Eduarda will have her first day of the fertile period of a 27-day cycle starting from the 8th day of the cycle.

Now that you know how to calculate the smallest cycle, let’s move on to the largest. For this case, the calculation is as follows:

32 (Longest cycle) – 14 = 18

With that, we know that the most likely day for ovulation of a 32-day cycle is the 18th day of the cycle. Then, the fertile period ends after it, that is, on the 19th day of the cycle.

As a safety measure, as in the case of regular cycles, it is ideal to add 2 days as a margin of error.

Finally, the two values ​​must be joined. The first day of the fertile period of the minor cycle and the last of the major cycle. So, Eduarda could be in the fertile period between the 8th and 21st day of the menstrual cycle.

Of course, the period will not last all these days, but since it is an irregular cycle, it is better to be safe than sorry!

Commonly Asked Questions About Fertile Period

Is it possible to get pregnant outside the fertile period?

No. For pregnancy to exist, fertilization is necessary, that is, the union of an egg and a sperm. If there is no egg to attach to a sperm, then pregnancy will not occur.

Is it possible to get pregnant during menstruation?

Yes, it can happen that women get pregnant even when they are menstruating. This is rare, but not impossible.

The women most likely to become pregnant even when menstruating are those with the shortest menstrual cycle time and menstrual duration greater than five days.

As sperm have the ability to survive in the woman’s body for at least 5 days and at most 7 days, it is possible that the woman becomes pregnant if she has unprotected sex in the last 2 days of her menstrual cycle.

How do I calculate my fertile period for the last 3 cycles?

Based on the last 3 cycles, you can average your fertile period in irregular cycles. To do this, just add the duration of each cycle and divide by 3. Remembering that this value is only an average and will not necessarily operate monthly in this way.

Will I get pregnant on the fertile day or period?

The fertile period is the phase in which ovulation occurs, at which time fertilization is possible. Having sex in the fertile period does not guarantee that fertilization will occur, as this also depends on other factors.

However, outside of that time, it is not possible to become pregnant as soon as there is no release of eggs.

Do my fertile days occur every month at the same time?

If menstruation is very regular, it is possible that fertile periods occur at very similar times every month. However, there is no way of knowing whether changes or alterations can occur.

It is often difficult to know exactly when it started and ended, especially since this phase can be more comprehensive.

In irregular cycles, knowing the fertile period can be even more difficult, as soon as there is no menstrual regularity.

Who takes contraceptives has a fertile period?

There are variables. However, 99% of women who take contraceptives respecting dates and times do not have a fertile period. The explanation is very simple: the contraceptive inhibits the hormones responsible for the maturation and release of the egg, that is, the woman does not ovulate and, without eggs, there is no fertility.

When does the fertile period end?

The fertile period ends when ovulation occurs. The organism shows the signs through the change in the vaginal mucus, which becomes whitish, resembling a watery glue or a moisturizing cream.

I menstruated twice this month, how do I know what my fertile period is?

Two periods in a month can mean that there was no ovulation period, since the fertile period is the pause between one period and another.

However, some women report ovulating normally, even if they menstruate twice a month. Such cases can occur due to irregularities in the cycle, for example: a cycle goes from 38 to 22 days.

What are the chances of getting pregnant by having sex close to the fertile period?

Sperm can survive up to five days in the woman’s body waiting for the egg. However, each organism has its particularities and, therefore, it is difficult to accurately measure the chances. So much so that a perfectly healthy couple can take up to a year to get pregnant, while others take only a few months.