A woman's fertile days are the days in the menstrual cycle when fertilization of an egg can take place. This cycle phase is also known as the “fertile cycle phase” or “fertile window”.

After ovulation (ovulation), the egg cell is located in the outer third of the fallopian tube, where it can be fertilized by a sperm for about 12-18 hours. The woman is not only fertile in these 12-18 hours, since the sperm in the cervical mucus of the uterus can survive for about five days, so that one can speak of about six days of the fertile days.

When are the fertile days?

With the start of a woman's menstrual cycle, her fertile life begins. She is then susceptible to pregnancy.
The cycle runs according to a certain scheme in which it goes through different phases. To understand when the fertile days occur in the menstrual cycle, it is important to take a closer look at the course of the cycle.

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With the onset of the first day of menstruation, the first phase of the cycle begins, the Desquamation phase. The old lining of the uterus is shed. After that, it matures under the influence of that formed by the ovary Estrogen the new lining of the uterus (Proliferation phase). At the same time, the egg follicle matures in the ovary, which contains the egg cell that later becomes important for fertilization (Follicular phase). Under the influence of other hormones, maturation processes occur, which ultimately result in the ovulation (ovulation) flow.
About 12 to 18 hours after ovulation, the egg can be fertilized by a sperm. Sperm can survive in the cervical mucus of the uterus for about 5 days. About 5 days before and 2 days after ovulation it can be one Fertilization of the egg come.
As already mentioned, the egg cell can also survive for a few hours, so fertilization can also occur shortly after ovulation.

Not every woman ovulates on the same day of her cycle. In 60% of cases, ovulation does not occur until after the 14th or 15th day of the cycle. With such a cycle, the fertile days would be between the 10th and 11th expected up to about the 18th day. However, this certainly cannot be narrowed down, since the Ovulation can vary widely can.

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Can you measure the fertile days?

There are several ways to roughly estimate your fertile days. There are a number of different ones Ovulation tests (e.g. Clearblue), which is based on hormonal concentrations in the female urinedetermine the time of ovulation (see above). This test is suitable to increase the likelihood of pregnancy, as there is increased fertility on the day of the positive test and on the following day. As Contraceptive method but he is not suitable, since it does not make any statement about the remaining fertile days and is also too imprecise.

There are other so-called Contraceptive computer (e.g. Persona) that work according to the same principle of hormone measurement.These also calculate around 6 to 12 days in the cycle, taking into account the lifespan of sperm, on which there is increased fertility. The user is then recommended to use additional contraception. However, this method of contraception is nowhere near as safe as hormonal contraception with the pill. Even if used correctly, pregnancy cannot be ruled out.

Other ways to measure the fertile days are the menstrual calendar and the symptothermal method.

Determination of the terrible days

To calculate the fertile days you can use a Menstrual calendar invest. There are now tools on various websites that calculate the fertile days using various parameters that have to be entered manually.

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There are several methods of calculating fertile days. One possibility is the so-called Knaus-Ogino method. This method assumes that if you have a regular cycle, ovulation will almost certainly occur on day 14 of your cycle. For the calculation, the cycle lengths of the last 12 months should be known and there should be no major fluctuations in the cycles. The first fertile day results from the shortest cycle length minus 18 days. The last fertile day results from the longest cycle to date minus 11 days.

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To illustrate this, here's a little one Calculation example:

  • with a shortest cycle length of 28 days, the first fertile day is on the 8th day of the cycle
    • 28 days minus 18 days = 10th day of the cycle
  • with a longest cycle length of 34 days, the last fertile day is on the 23rd day of the cycle
    • 34 days minus 11 days = 23rd day of the cycle

The fertile days are between the 10th and the 23rd day of the cycle. According to this calculation, the sterile days are before the 10th and after the 23rd day of the cycle.
However, the method is considered to be very insecure and is in no way used for safe contraception. However, it can be consulted to increase the likelihood of pregnancy.

In addition to the Knaus-Ogino method, you can also use a Ovulation calculator determine. This method can also only an approximate indication of the fertile days. To do this, you need to know the first day of your period and the length of your cycle. The first day of your period is the first day of your cycle. Ovulation takes place on the 14th or 15th day. The fertile days are around 3 to 4 days before and one day after ovulation. However, the information from different ovulation calculators varies here. Some report increased fertility up to 3 or 4 days after ovulation. Besides, the method is not particularly reliablebecause at least 40% of women ovulate is not certain to occur on day 14 of their cycle. In addition, the cycle length also often varies. An ovulation calculator can be used to increase the chances of conceiving, but this is not a reliable method of contraception.

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Test to determine the fertile days

There are a number of so-called ovulation tests that can be used to determine ovulation LH concentration in the urine determine. It is the luteinizing hormone, one of the important cycle hormones, which is present in increased concentrations during ovulation. There are both Strip teststhat indicate ovulation by a rash of color, as well digital ovulation testsworking with symbols on a digital display. To do the test, you need to know the first day of your period and the last day before your next period starts. This is how you determine the cycle length. There is a table attached to every ovulation test, from which you can then read off when the test can be carried out.
With a cycle length of 28 days, this is, for example, the 11th day of the cycle. Then ovulation is possible at the earliest. From this point on, the test can be carried out. It is best to do this the same time every day perform. It offers itself to the Morning urine to use, since this is where the hormone concentration is highest.
Excessive drinking should be avoided before urinating as it can dilute the urine.

The test then shows whether the LH concentration is increased or not. If it is positive, it means that the day of the positive test, as well as the following day, are the most fertile days of the cycle. The likelihood of pregnancy is increased during these two days. If the test turns out negative, it must be repeated the next day at the same time with a new test stick. The prices for such ovulation tests are between 10 and 40 euros, depending on the manufacturer. They are also unsuitable as a method of contraception.

Symptoms of the fertile days

The fertile days as such are not indicated by specific symptoms. So it's kind of like impossible to tell from physical symptoms.

Ovulation (ovulation) can be caused by the so-called Middle pain express. This is one-sided as a kind of pulling or convulsive Abdominal pain described, which can be clearly distinguished from other pain. It can last up to a few hours. However, not every woman experiences ovulatory pain like this.

Another physical phenomenon that can occur is a minor one Ovulatory bleeding. This can sometimes only be seen as a discreet darkening of the natural discharge. Another possible symptom is liquefaction of the cervical mucus. However, this is almost never really visible because the mucus is not always visible. If it should be visible, it shows a spinnable consistency. Individual symptoms such as chest pain, increased sexual interest, or other phenomena cannot be reliably dated to ovulation or the fertile days, but may be related.

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Cervical mucus

The so-called cervical mucus is formed on the cervix by special glands and is what most women know as discharge. The cervical mucus changes its consistency in the course of the cycle due to hormonal influences. On infertile days, the cervical mucus has a rather firm consistency, so that it can close the cervix as a natural barrier.
On the fertile days around ovulation, the consistency of the mucus changes. It becomes crystal clear and thin, so that it pulls threads. This is also known as spinnable. During ovulation, threads up to 15 cm long can be pulled between the fingers. The sperm can then travel more easily into the uterus along these small, parallel threads.

Learn more about Change in discharge during ovulation

As part of various methods of natural contraception, the consistency of the cervical mucus is also assessed. However, these methods are considered to be very unsafe and unreliable. If, in addition to the consistency of the cervical mucus, the determination of the basal temperature is used for natural contraception, the reliability of the contraception increases. Such procedures are called symptothermal methods.

You might also be interested in: Ovulation and temperature - what is the relationship?


There are various natural methods of contraception that aim to limit the fertile and infertile days of the female cycle. Ovulation calculators, menstrual calendars and symptothermal methods are used, which focus on assessing the cervical mucus and measuring the basal temperature. Symptothermal procedures are considered to be relatively safe in the case of sexual abstinence during the fertile days. Other methods such as ovulation calculator and menstrual calendar, but also the sole assessment of the cervical mucus or the basal temperature, are not suitable as methods of contraception due to their inaccuracy.

You may also be interested in this topic:

  • Can you postpone ovulation?

Cerazette is a contraceptive method in tablet form. You should also deal with this promising form of contraception before you decide on a variant. For the most important information, read: Cerazette - the most important information at a glance

Apps for fertile days

There are now different apps that use different information from the user to manage the Increase the likelihood of pregnancy want. These are combinations of menstrual calendars or ovulation calendars, which can be supplemented with individual information such as complaints, consistency of the cervical mucus or the basal temperature. The more information the user can enter into such an app, the more precisely the fertile days can be narrowed down.

Such apps are suitable to determine the likelihood of pregnancy in women who want to have children to increase. However, they are too imprecise for contraception and depend on the information provided by the user. The following is a small overview of a few current apps, which by no means claim to be complete: cycle calendar from ELTERN, Clue, Glow, Lily - your personal and private period tracker.

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After stopping the pill

In the "pill“Is about a hormonal contraceptivewhich prevents pregnancy. Most combination products prevent ovulation. They create a regular cycle of 28 days, during which one tablet is taken every day for 21 days. There is a break for the remaining 7 days, during which there is a so-called withdrawal bleeding. This is usually much easier than menstrual bleeding.
There are also single substance preparations (so-called Mini pills), which primarily work by thickening the cervical mucus. Newer mini pills also prevent ovulation. So there are no fertile days while taking the pill. The implantation of a fertilized egg is not possible. After stopping the pill, this protection is no longer guaranteed, so ovulation takes place again.

In the first few months after stopping the pill, there may be irregularities in the length of the cycle, making it difficult to estimate the time of the fertile days. However, these irregularities are natural and can occur without a particular event.

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