How to Calculate a Woman's Fertile Days | Oh Mama Matrona

Knowing your menstrual cycle well and understanding how to calculate a woman's fertile days will also help you identify the date of your ovulation, which is key when trying to conceive.

You may have heard that "the most fertile day is the day of ovulation," which is typically day 14 in a 28-day cycle. However, my friend, I’m here to tell you that NOT all women ovulate on this day. Some ovulate on day 8, while others on day 18.

What?! Yes, you heard that right. Each woman and her circumstances make her unique, and even the same woman may experience "things" that can modify her cycles.

That’s why it’s crucial to listen to your body, note the different sensations you have (even if they seem insignificant), and pay attention to everything that happens to us (not just physically, but also emotionally).

And this emotional aspect gives us many clues about how we are feeling. Don’t you notice that when you are ovulating, you find your partner even more attractive?

Knowing your cycle also means understanding that at the time of ovulation, you have a higher sex drive than, for example, in the premenstrual phase, which is characterized more by fatigue and low sexual appetite.

But let’s start from the beginning…

Table of Contents

• What is ovulation?
• Signs that indicate you are in your fertile period
• How to calculate a woman's fertile days
• How to calculate the most fertile period of a woman
• What are the days with the lowest probability of pregnancy?
• Methods to calculate a woman's fertile days
• My advice for calculating fertile days

What is Ovulation?

Ovulation is the moment when, thanks to hormonal activity, the egg finishes maturing and leaves the ovary towards the fallopian tubes, where it can meet with sperm. If this encounter occurs, fertilization may take place.

To reach this point, the body goes through different phases of the menstrual cycle. The first is the follicular phase, during which the follicle-stimulating hormone activates several follicles, and some begin to grow and develop.

Meanwhile, estrogens thicken the endometrium to prepare it for a possible pregnancy. Later, the luteinizing hormone causes the mature egg to be released from the follicle and begin its journey towards the fallopian tubes, where sperm may be waiting.

Ovulation itself lasts about 24 hours, and the ovum can be fertilized within 48 to 72 hours. To know if you are ovulating, it’s important to pay attention to specific changes or signals from your body.

Signs That Indicate You Are in Your Fertile Period

When you are in your fertile period, your body sends you signals such as the type of cervical mucus, discomfort or pain in the lower abdomen, increased breast sensitivity, and even mood changes.

Here’s a complete list of the most common signals you can observe to know your fertile days:

1. Cervical mucus changes: In the days before and after ovulation, it is noticeably more abundant, clear, and stretchy (like egg white).
2. Pain, discomfort, and/or bloating in the lower abdomen during ovulation (the moment and place where the follicle detaches).
3. An increase in basal temperature of 0.3-0.5ºC after ovulation.
4. Increased breast sensitivity and swelling.
5. The cervix is higher and softer, and its opening widens.
6. Light spotting.
7. Increased sexual desire (due to the rise in estrogens).
8. Mood changes (due to hormonal fluctuations).
9. Lower back pain.
10. Hormonal changes: the onset of the LH peak is the most reliable indicator of ovulation.
11. The appearance of the vulva, for example, does not usually give clues that you are ovulating.

Some women easily identify these signals, while others barely perceive them, and both situations are completely normal.

If you find it difficult to recognize them, if you have hormonal disorders, fertility issues, or simply want to better understand your cycle to calculate your fertile days, it’s best to consult with an expert midwife in fertility. And, as you know, the team of professionals at Oh Mama Matrona can support you in this process.

As we mentioned, ovulation usually occurs mid-cycle. In regular 28-day cycles, this can happen around day 14. However, not all women have such regular cycles: some women have their period every 25 days and others every 30.

If you are one of the latter, it may be a bit more challenging to calculate your fertile days.

Our first recommendation for calculating your fertile days is to know your menstrual cycle well. Be careful! This is not only important for women who wish to conceive or those who want to avoid pregnancy naturally… it’s for your health!

How to Calculate the Most Fertile Period of a Woman

The way to calculate fertile days varies depending on the regularity of the cycle, so it’s advisable to separate both scenarios.

Calculate if Cycles Are Regular

In general, the fertile period spans about 2-6 days around ovulation, meaning the 5 days prior and the day of ovulation itself.

To calculate fertile days in regular cycles, it’s important to know the length of your cycle (from the first day of bleeding to the day before your next menstruation).

Ideally, you should track it for several months to obtain a reliable average.

Once you have that, subtract 14 days from the estimated date of your next period: this way, you can calculate your approximate ovulation day.

In women with regular cycles, the fertile window is usually the 5 days leading up to ovulation and, to a lesser extent, the hours following it. It’s advisable to have intercourse during those days, especially in the days leading up to ovulation.

Calculate Fertile Days in an Irregular Cycle

Women with irregular cycles may find it a bit more challenging to know exactly when their ovulation day is and, therefore, to know their fertile period. Generally, to calculate fertile days, you should subtract 14 days from your shortest cycle and 18 from your longest cycle (adaptation of the Ogino Method).

You might find it more useful (especially in these cases) to pay attention to the signals your body sends you:

• Observe how your cervical mucus behaves.
• Monitor your basal temperature.

However, in these cases, it’s most reliable to consult with a fertility specialist who can help you gain a better understanding of your cycle and your fertile days.

What Are the Days with the Lowest Probability of Pregnancy?

If you have regular cycles, at the beginning of the cycle, from the first day of your period to about 6 days before ovulation. The probability also decreases from the second day after ovulation until the end of the cycle.

These calculations are indicative and should not be used as the sole contraceptive method. Also, remember that sperm can live for several days inside a woman’s body.

Methods to Calculate a Woman's Fertile Days

There are several tools to calculate the most fertile days. The most effective, as mentioned, is to consult with an expert who can conduct a thorough evaluation of your medical history, taking into account medical, surgical, and family backgrounds… Because yes, my friend, all of this influences your fertility.

1. Calendar or Rhythm Method

The calendar method, also known as the rhythm method or Ogino-Knaus method, is a natural family planning method that involves calculating the fertile days of the menstrual cycle to avoid pregnancy by abstaining from penetrative sexual intercourse during that period.

To use it correctly, it’s necessary to track menstrual cycles for at least 6 to 12 months to calculate the ovulation window, subtracting 18 days from the shortest cycle and 11 days from the longest cycle to determine the days of abstinence.

However, its effectiveness is low and it is not recommended as the sole method for women with irregular cycles.

2. Basal Temperature Method

Keeping track of your temperature can also be useful to know if you are ovulating. However, it’s not infallible. The progesterone synthesized after ovulation impacts in such a way that the body temperature increases by 0.3 – 0.5 ºC. This temperature rise indicates that the fertile phase has ended.

To do this correctly, it’s recommended to take your temperature immediately upon waking and at rest; the thermometer (always the same) should be placed in the mucous membranes (mouth) and preferably at the same time each day.

3. Cervical Mucus Method

Another aspect to consider when trying to conceive is cervical mucus. Observing its consistency will give you clues about where you are in your cycle. On fertile days, the mucus will be clearer (raw-like), similar to egg white and stretchy, while on non-fertile days, it is less abundant or more pasty.

4. Ovulation Tests (LH Tests)

LH strips (luteinizing hormone) detect the peak of this hormone in urine to predict when you will ovulate and, therefore, what your fertile days will be.

They are also known as ovulation tests: if two marked lines appear, it means that the egg will be released in the next 12-36 hours, making this the optimal time to have intercourse if you are trying to conceive.

While this can be a helpful tool for both women with regular and irregular cycles, our recommendation is to reserve them for a secondary role for your peace of mind.

We consider it more important to know your cycle well and pay attention to the signals from your body (not only physical but also emotional) so that the process doesn’t become mechanical and rigid.

5. Symptom-Thermal Method

The symptom-thermal method is a natural family planning approach that relies on the observation and recording of various fertility indicators we just discussed, such as basal temperature, cervical mucus, and cervical position.

To assess the latter, you can perform a self-examination to evaluate the height of your cervix. On fertile days, it is high, open, and softer.

It’s important to keep a record to identify patterns throughout the different phases of the cycle. In this record, you will note the physiological changes that happen to your body at least 6 months before trying to conceive to ensure you know your cycle well. For this, it can be very useful to use apps designed for this purpose.

6. Fertility Apps

A tool that can be useful for understanding your cycle and that can also assist you in your journey to conceive are fertility apps. In the last decade, this type of app has proliferated, allowing for a much more agile and easy tracking of your cycle.

7. Fertility Calculator

The ovulation and fertile days calculator can help you as a quick reference if you want to make an approximate estimation. It allows you to see at a glance the approximate date of your next ovulation and a general idea of your fertile window.

Still, it’s important to remember that this is just a...