Measuring Basal Body Temperature: All about the temperature method

Basal body temperature is an important part of the female cycle. It is used to determine fertile and non-fertile days as well as ovulation. BBT changes during the cycle in line with the hormones and thus shows you your ovulation, the different cycle phases and your menstruation.

These temperature measurements can provide you with valuable information to increase or rule out the likelihood of pregnancy, and to get to know your body's unique rhythm.

What is the basal body temperature?

The basal body temperature (BBT) marks the low point of your body temperature during the day and occurs during a longer period of rest.

During the night, your body comes to rest and your body temperature reaches its lowest point. As the basal body temperature is measured every morning directly after waking up, it is also called the "wake-up temperature." Shortly after waking up and making your first movements, your core body temperature rises again.

Due to the measurable influence of the sex hormone progesterone on the basal body temperature, the wake-up temperature varies according to a recurring pattern over the course of your cycle. You can therefore use this method to accurately determine the follicular phase, your ovulation, and the subsequent luteal phase based on a slight rise in temperature.



Why should you track your basal body temperature?

Basal body temperature is a valuable method for understanding female fertility and individual cycle health and offers many benefits.

Taking your temperature allows you to gain a deeper understanding of your own body and discover recurring patterns and exciting correlations.

Basal body temperature, desire to have children & family planning

Taking your basal body temperature is particularly valuable for couples who are planning a pregnancy and want to increase their chances of conception.

The temperature method shows you if and when you are ovulating. So if you want to get pregnant, you can time sexual intercourse to coincide with the fertile phase, i.e. the days around ovulation. This can increase the likelihood of a faster pregnancy.



Cycle knowledge also forms an important basis for advice from specialists, for example as part of fertility treatment, should this be necessary.

 Using your basal body temperature to achieve an understanding of your fertile days allows you to actively take control of your personal family planning and reproductive health.



Basal body temperature and irregularities in the menstrual cycle

Contrary to the assumption that the length of a menstrual cycle is approximately 28 days, reality shows that this is not the case for many women. The female cycle is just as individual as the female body and an an irregular cylce does not necessarily mean a reduction in fertility or health.

However, an irregular cycle can cause family planning difficulties for some women, as it leads to fluctuations in cycle length and uncertainty about the timing of ovulation or periods.

Daysy can work with irregular cycles.



Basal body temperature & health problems

An unusual basal body temperature pattern, for example unusually high or low basal body temperatures or the lack of a rise after ovulation, can indicate hormonal imbalances and related health problems. Examples include thyroid disorders or polycystic ovary syndrome (PCOS).

As an important indicator of health, comparable to breathing or heart activity, basal body temperature provides valuable information about the state of the menstrual cycle as the fifth vital sign. A regular and healthy cycle signals normal functioning of hormonal production and regulation in the body.

Measuring the basal body temperature curve and the statistics in the optional DaysyDay app can help you identify potential health problems at an early stage. If you notice any unusual cycles or temperature measurements, you can contact us directly for a free cycle analysis or visit a doctor to discuss these abnormalities.

Basal body temperature & PCOS

For women diagnosed with PCOS (Polycystic Ovary Syndrome), continuous measurement of basal body temperature is particularly important. Those affected often have irregular and long cycles, making it difficult to determine when and if ovulation has taken place.

Many women with PCOS use Daysy to monitor the success of lifestyle changes or drug therapies. Daysy visualizes and tracks your cycles based on your daily basal body temperature. It shows you whether ovulation has taken place and how long your cycle was in total. This information is very useful not only for you, but also for your gynecologist.

Basal body temperature and understanding your cycle

By continuously recording your basal body temperature, you can quickly recognize recurring patterns that help you to better interpret and understand your own moods and physical signs.

This knowledge enables you to take special care of yourself during challenging cycle phases and can make it easier for you to deal with mood swings, energy levels and other cycle-related symptoms.

In this way, awareness of your own cycle not only contributes to reproductive health, but also promotes your overall physical and emotional well-being.

How is basal body temperature measured?

Basal body temperature is measured immediately after waking up, while lying down, using a special basal thermometer or cycle computer such as Daysy. For a reliable measurement with a basal thermometer, it is important that the measurement is taken under the same conditions as possible and is not distorted by physical activity or external factors such as room temperature and bed warmth.

Conveniently, these external factors have no influence on the measurement of basal body temperature with Daysy, as it recognizes the personal temperature optimum. The special thermal sensor waits during each measurement until the final temperature has stabilized. Even if the body temperature drops shortly after a maximum value, for example due to breathing in cold air, the result is not affected.

This is how temperature measurement with Daysy works:

  1. As soon as you wake up, take Daysy in your hand, place the sensor under your tongue as far back as possible and close your mouth. 
  2. After less than 60 seconds, you will hear a soft tone and Daysy will show you your fertility status for the next 24 hours. 
  3. Simply connect Daysy to the DaysyDay app and view your cycle data in detail using the temperature curve or cycle summaries. 

You can easily determine your menstrual cycle with an all-in-one device.

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How does the basal body temperature change during the menstrual cycle?

The cyclical temperature fluctuations are approximately 0.2° to 0.45° degrees Celsius (0.4 to 1 degree Fahrenheit)  These fluctuations are triggered by the hormone progesterone, also known as the corpus luteum hormone. This subtle increase directly after ovulation can be tracked with cycle computers such as Daysy.

With the temperature curve, you can clearly follow the individual phases of your cycle and gain exciting insights into your body.

How does the basal body temperature indicate ovulation?

In the first phase of the cycle, starting with menstruation until ovulation (follicular phase), the basal body temperature remains relatively constant at around 36.5° Celsius (97.7°F) . After ovulation, the body begins to produce more of the hormone progesterone, which acts on the body's thermoregulation center and causes the basal body temperature to rise by around 0.2° to 0.45° (0.4 to 1 degree Fahrenheit).

To identify your ovulation, it is crucial that you recognize this "ovulation spike" based on the temperature curve.

Daysy shows you with a red flashing light, so you don't have to find out for yourself when you are ovulating. Daysy was developed to not only identify the predicted day of ovulation for you, but also to recognize the entire potentially fertile window.

How does the basal body temperature indicate your period?

After ovulation, the temperature remains elevated for around 12 to 16 days until the start of your menstruation. If no fertilization of the egg has taken place, the progesterone level decreases again. A subsequent drop in temperature indicates that your period is about to start.

Thanks to this natural signal, you are well prepared for the start of your period.

How does the basal body temperature show you that you are pregnant? 

Basal body temperature is a reliable way of detecting pregnancy at a very early stage. If your period is absent and your basal body temperature remains at a consistently high level for more than 18 days, this could indicate an early pregnancy. You may even notice a second rise in basal body temperature caused by the implantation of the fertilized egg in the uterus. Implantation takes place around 6 to 12 days after ovulation.

Daysy indicates a possible pregnancy when all the lights (red, green and yellow) are flashing. In your temperature curve, a probible pregnancy is indicated by the blue color.

It is important to note that Daysy is not a pregnancy test. To be on the safe side, you should have your pregnancy confirmed by a standard pregnancy test or a visit to your doctor.

What disruptive factors influence basal body temperature?

Your basal body temperature can be affected by certain factors such as stress, illness and medication.

Illnesses, especially if they are accompanied by a fever, can lead to a temporary increase in basal body temperature. If you are ill, the DaysyDay app will automatically inform you that you should take your temperature with a standard thermometer. Conveniently, temperatures above 37.8°C or below 35°C are automatically excluded from the calculations by the algorithm.

Daysy will not let you down in any of these circumstances. No matter whether you have stressful days or short nights or are struggling with the ups and downs of life. - Daysy is always there for you.

Daysy is designed so that it can also be used by new moms or shift workers.

Basal body temperature tracking as the key to understanding your personal cycle. 

No matter what phase of life.

Measuring your basal body temperature allows you to understand the cycle-related processes in your body and gives you control over your reproductive health.

From planning a pregnancy to early detection of hormonal imbalances and promoting your emotional well-being - Daysy supports and accompanies you in all situations.




Discover the fascinating nuances of your body's signals with a glimpse into different basal body temperature curves. From the 'typical' curve showcasing the rise of ovulation, to unexpected drops and rises that reveal thyroid function, this exploration unveils insights into fertility, health, and well-being.

Your body resets your temperature when you get sufficient sleep. Check your BBT chart, and you’ll see that it’s not constant but varies within a narrow range. BBT typically shows a biphasic pattern that matches the two phases of your menstrual cycle, and your hormones are responsible. Let’s walk you through the process.

Discover how basal temperature can provide insights into your thyroid function. Our thyroid may be small, but it plays a crucial role in metabolism, health, and fertility.