How can you determine your fertile days with natural family planning?

Would you like to get to know your body better and understand your fertility without hormones?

Then natural family planning is just the thing for you. 

More and more women are looking for natural, hormone-free alternatives to experience their sexuality in a self-determined way, without any side effects.

Natural family planning (NFP) includes modern methods of family planning based on the observation of natural signs and symptoms of the menstrual cycle (2). 

By closely observing your body signals and systematically evaluating your cyclical changes, you can determine your ovulation and therefore your fertile and non fertile days. 

Natural family planning offers you a hormone-free alternative that does not interfere with your natural cycle. It allows you to promote your health and well-being in a holistic way. 

Experience the freedom and self-confidence that comes with understanding and taking control of your own body

What are the basic principles of the NFP method? 

Your cycle is controlled by a complex interplay of hormones, messenger substances and bodily functions, with the hormones progesterone and estrogen playing a central role. 

This interplay of hormones leads to recurring patterns during your cycle, with ovulation being particularly important for natural family planning. Typically, one ovulation occurs per cycle, releasing a single egg. However, in rare instances, two eggs may be released in quick succession.

The time around ovulation is crucial for pregnancy or contraception. An egg only remains capable of fertilization for around 12-24 hours and travels through the fallopian tube to the uterus during this time. 

Sperm, on the other hand, can survive in the uterus for up to 5 days to wait for the egg. 

This results in a period of 6 days per cycle during which fertilization is possible: 5 days before your ovulation plus the day of ovulation itself (1).  

The days before ovulation and the day of ovulation itself are considered fertile, while the time after ovulation is considered non fertile. 

Fertilization is most likely to occur on the 2 days before ovulation (3).

If you want to use natural family planning for contraception and to avoid pregnancy, you have to avoid unprotected sex during your fertile window and use contraceptives such as condoms or diaphragms.

If you want to have children, you can find out your fertile window and significantly increase your chances of getting pregnant.

The NFP method uses the biological processes of your body to determine the exact time of ovulation. By observing and documenting various physical signs and symptoms, such as temperature changes and cervical mucus, you can narrow down the fertile period.

If you are prepared to understand your body's signs, you can shape your family planning in a self-determined and effective way.

Which body characteristics of your menstrual cycle tell you about your ovulation? 

In order to use natural family planning, it is crucial to understand exactly how your menstrual cycle works. The hormones that regulate your cycle and trigger ovulation have a direct impact on your body.

Your basal body temperature changes

Basal body temperature is the lowest body temperature during the day, measured after a long period of rest, typically after waking up and before getting out of bed. 

Progesterone has a measurable effect on this basal body temperature. 

Immediately after ovulation, the production of progesterone increases, causing your basal body temperature to rise by around 0.4°F to 1°F (3).  This increase remains until approximately 1 to 2 days before the start of your next menstruation (3).  

If your basal body temperature remains elevated, you know that ovulation has occurred and your fertile phase for that cycle is over (4).  

Your cervical mucus changes

Your cervical mucus is produced by the cervical glands in the cervix and reacts to the hormones estrogen and progesterone. At the beginning of your cycle, cervical mucus is sticky and thick (3).  

Shortly before ovulation, it becomes clear, stretchy and multiplies, similar to raw egg white. After ovulation, the mucus returns to its sticky form and becomes less thick, signaling that your fertile phase is coming to an end (3). You can check these changes directly at the vaginal entrance. 

The special texture of the cervical mucus during the fertile window helps the sperm on their way to the egg and makes it easier for them to survive.

 

What NFP methods are available?

The natural methods of NFP offer you the opportunity to understand your cycle and manage fertility without hormonal intervention. Among these methods, there are different approaches, each based on your biological signs.

What is the rhythm method?

The rhythm method, also called calendar method, calculates the fertile and not fertile times in the cycle. It is the oldest form of contraception and takes into account the shortest and longest menstrual cycles of the last 12 months. 

The fertile days are determined as the period from the shortest cycle minus 18 days to the longest cycle minus 11 days. 

During these days, sexual intercourse should be avoided if contraception is desired or another contraceptive method should be used.

This method requires regular cycles and is significantly less reliable than modern contraceptive methods.

What is the classic temperature method?

With the basal body temperature method according to Döring, you measure and document your basal body temperature every day. You can take this measurement orally, vaginally or rectally. 

It is important to use a precise thermometer with at least two decimal places, as the temperature rise after ovulation is only around  0.4°F to 1° and a conventional thermometer is not sufficiently accurate.

After you have measured your basal body temperature (at least 3 minutes), enter it carefully in a cycle sheet. However, influences on your lifestyle such as traveling, alcohol, stress or little sleep can easily falsify the accuracy of your measurement results.

How does the cervical mucus method work?

The cervical mucus method, also known as the Billings ovulation method, is based on determining your fertile days by observing your cervical mucus. 

This method focuses exclusively on cervical mucus and does not take any other factors into account.

Women who want to use this contraceptive method must not only be able to differentiate between dryness, sticky moisture and wetness, but also be able to assess the different textures of the mucus.

It is important to know that this method is quite demanding. You need to collect, assess and record your cervical mucus daily. Cervical mucus can also be altered by various influences such as medication or disease, which makes this method prone to error. It also takes time and practice to use it correctly.

Every woman has a “typical” mucus pattern that differs from that of other women. It depends on perception, observation and description of personal changes.

Basically, if no mucus is observed, it can be assumed that you are in a non fertile cycle phase. However, as soon as mucus or any sensation of moisture occurs, this indicates the start of the fertile days. This also applies to less fertile mucus, which feels fluffy, sticky and dense; conception cannot be ruled out here either.  

How does the symptothermal method of natural family planning work?

The symptothermal method according to Rötzer is a combination method and a reliable way of determining the fertile window in the menstrual cycle. It combines the observation of cervical mucus with the measurement of basal body temperature.

Temperature and cervical mucus are evaluated in relation to each other. 

You measure your basal body temperature every morning before getting up and also monitor your cervical fluid. You then enter this data in a table. Your fertile phase begins when you notice fertile cervical mucus and ends when the cervical mucus changes and your basal body temperature remains elevated for at least three days.

Self-examination of the cervix can provide further information about the fertile window.

In order to reliably determine your fertile days, it is important to continuously collect and evaluate this data for at least six to twelve months.

This method offers you a reliable way of identifying your fertile days. However, it requires a great deal of time and discipline over several months.

How can our fertility tracker Daysy with the Fertility Tracker method support you in using natural family planning?

As you can see, using NFP methods can be a challenge as they require a lot of time and knowledge. 

This is where our fertility tracker Daysy comes into play, taking all the hard work out of the equation.

With the Fertility Tracker method, you can easily and reliably determine your cycle and your fertile days.  

Automated and accurate temperature measurement

Daysy uses your basal body temperature as the basis for calculating your fertile and not fertile days. Thanks to the highly sensitive thermosensor, the measurement is particularly accurate and fast: you measure your basal body temperature under your tongue every morning before getting up in just 60 seconds.

The sensor waits until the temperature has stabilized and then provides you with your fertility status directly on the device.

Convenient and time-saving application

In contrast to traditional NFP methods, which are often time-consuming and error-prone, Daysy offers a convenient and uncomplicated solution. With Daysy, you don't have to write down and manually analyze your data. All you have to do is take your temperature every morning and enter whether you have your period. Daysy shows you immediately whether you are fertile or not.

What's more, with Daysy you don't have to read up on natural family planning first. In the beginning, the algorithm has to get to know your body and will show you many “yellow days” (learning phase). 

The more continuously you use Daysy over several months, the more days Daysy will mark as green (non fertile) days and narrow down your fertile window further and further. This is why Daysy is accurate from the first measurement.

Support from the DaysyDay app

With the free DaysyDay app, you can synchronize your temperature data and view your cycle status, temperature curve and forecasts. The app makes it easy for you to monitor your cycle and evaluate it in the long term. Without having to enter your data manually, you can easily see your fertile days, the length of your cycle and the time of your period.

You can also track the observation of your cervical mucus in the app. This means you have all your data in one place. 

Since the observation of cervical mucus is very individual and often prone to error, our algorithm does not include this information in the calculation.

Intuitive algorithm and high security

Daysy combines daily temperature measurement with a self-learning algorithm based on over 35 years of cycle research and over 10 million cycles. This enables Daysy to determine the transition from fertile to not fertile days very precisely. Daysy also automatically adjusts the calculations in the event of irregularities such as illness or lack of sleep.

In addition, Daysy not only focuses on your current cycle, but also includes past cycles in the calculation. This means that fertile days can be determined more reliably and predicted more easily. 

Daysy makes natural family planning smart, simple and reliable. 

You enjoy the benefits of the NFP method without the time and uncertainty of traditional methods. You can manage your fertility in a self-determined and hormone-free way.

(1) Sung, S. & Abramovitz, A. (2023, 24. Juli). Natural family planning. StatPearls - NCBI Bookshelf. https://www.ncbi.nlm.nih.gov/books/NBK546661/

(2) Natürliche Familienplanung. (2018, 9. Juli). Frauenärzte Im Netz. Abgerufen am 22. Juli 2024, von 

(3) Simmons, R. G. & Jennings, V. (2020). Fertility awareness-based methods of family planning. Baillière’s Best Practice & Research. Clinical Obstetrics & Gynaecology/Baillière’s Best Practice And Research in Clinical Obstetrics And Gynaecology, 66, 68–82. 

(4) Peters, A. & Mahdy, H. (2023, 13. November). Symptothermal contraception. StatPearls - NCBI Bookshelf.