Natural Family Planning
Understand your fertile window, naturally.
Natural Family Planning, or NFP, is a collective term for family planning methods that do not interfere with the physiology of the female hormonal cycle. Many women choose this approach because they want to understand their bodies more clearly, protect their hormonal balance, and make more informed choices about fertility, cycle health, and timing.
Hormone-free
What is Natural Family Planning?
Natural Family Planning is based on understanding when pregnancy is possible within the menstrual cycle. A woman is only fertile for a limited number of days in each cycle, which means that timing plays a central role in both trying to conceive and avoiding pregnancy naturally.
These methods focus on observing the body instead of suppressing it. For many women, that makes NFP feel like a more conscious and body-aware approach to fertility, health, and wellbeing.
A more conscious, body-aware approach to fertility.
Observe — don't suppress
The cycle at a glance
Menstruation
Days 1–5
Follicular phase
Hormone preparation
Fertile window
5 days before and on the ovulation day
Luteal phase
24h after ovulation - next menstruation
Cycle timing
Why timing matters
Pregnancy cannot happen on every day of the month. Sperm can survive in the female body for maximum 5 days, while the egg can only be fertilized for a short period direct after ovulation, which is why the fertile window lasts only a limited number of days.
Understanding when that window begins and ends can make an important difference. That is why many women want support in identifying expected ovulation, fertile days, and the point at which the fertile phase has likely passed.
The technology
How Daysy supports Natural Family Planning
The Daysy Fertility Tracker supports Natural Family Planning by measuring basal body temperature and combining that data with confirmed menstruation days. Based on these inputs, Daysy helps distinguish fertile and non-fertile days and gives a daily indication that is easy to follow.
Daysy uses a precise sensor and a smart internal algorithm designed to evaluate your cycle in real time. According to Daysy, the internal algorithm has been tested systematically and is described as 99.4% accurate in distinguishing fertile days.
Basal body temperature
A daily reading reveals the small shifts that surround ovulation.
Precise sensor
Engineered to detect the subtle changes that define your fertile window.
Smart algorithm
Evaluates your cycle in real time, refined through years of cycle data.
Clear signals
Simple daily guidance through color
One of the strengths of Daysy is that it translates complex cycle data into a simple daily color indication. Green indicates non-fertile days, red and yellow indicate fertile days, and flashing violet asks whether menstruation is happening.
This gives women a more practical way to follow Natural Family Planning without manually interpreting temperatures every single day. The device is designed to make fertility awareness easier to understand and easier to use in daily life.
Green
Non-fertile day
A day on which conception is not expected, based on your cycle data.
Red & Yellow
Fertile days
Days within the fertile window, when conception is possible.
Flashing Violet
Menstruation check
Daysy asks whether menstruation is happening — confirm with one button.
Measuring
How to measure correctly
To use Daysy properly, you measure your basal body temperature immediately after waking up in the morning and before getting out of bed or becoming active. Daysy states that measuring after at least one hour of uninterrupted sleep is important for a reliable reading.
The sensor is placed under the tongue and the mouth stays closed during the measurement. Daysy explains that the measurement is completed once the temperature has stabilised, which typically takes around 60 to 90 seconds.
01
After at least 1h of sleep
Sound, uninterrupted rest.
02
Right after waking
Before getting out of bed.
03
Sensor under the tongue
Mouth closed during measurement.
04
60–90 seconds
Until temperature stabilises. Confirmation signal.
More than counting days — Daysy learns from your cycles over time.
Calendar method
Days only
Daysy
Days + temperature + learning algorithm
Precision
Why Daysy goes beyond the calendar method
Natural Family Planning should not be reduced to simply counting days in a period app. Daysy explains that its technology is more precise than methods based only on recorded menstruation days, because it also takes basal body temperature and a 3-step analyzing algorithm into account - all in 1 device.
That matters because real cycles do not always behave exactly as expected. Daysy states that the internal algorithm also learns from previous cycles, anticipates changes and uses millions cycle examples to analyze, which helps create a more personalised real picture.
Insights
Support in the app
In combination with the DaysyDay app, the device becomes even easier to use. The app helps users view fertility status, a cycle calendar, a temperature curve, and personal notes in a clearer and more visual way.
Daysy explains that measurements remain stored in the device, so users do not need to sync every day. Syncing becomes available after at least one successful measurement and can be done whenever the user wants.
Inclusivity
Also relevant for irregular cycles
Natural Family Planning is not only for women with highly regular cycles. Daysy also presents its tracker in relation to irregular cycles and even mentions PCOS, positioning the device as a useful tool for women who want more insight into patterns that feel less predictable.
For these women, better cycle awareness can bring more clarity and confidence. Instead of guessing, they can start observing real signals from the body and follow changes over time.
From guessing to observing real signals.
- Useful for irregular cycles
- Mentioned in relation to PCOS
- Builds awareness over time
A possible pregnancy indication after 18+ days of elevated temperature.
Relevant for fertility awareness and for women actively trying to conceive.
Conception
For women who want to conceive
Natural Family Planning can also be valuable when there is a current or future wish to conceive. Understanding when ovulation is expected and when the fertile window is open can help women approach conception in a more informed and supportive way.
Daysy also states that a possible pregnancy indication may appear when the basal body temperature remains elevated for more than 18 days. This makes the tracker relevant not only for fertility awareness, but also for women who are actively trying to conceive.
Important
An important note about protection
Daysy describes its fertility trackers as hormone-free and fully natural, but not as contraceptives. In the context of Natural Family Planning, the site explicitly advises using a barrier method such as condoms on fertile days when pregnancy is not desired.
That distinction is important for clear communication. The purpose of the device is to support fertility awareness and cycle understanding, while pregnancy prevention decisions still require responsible use and informed choice.
FAQ
Frequently Asked Questions
Clear answers to the most common questions about Natural Family Planning with Daysy.
Daysy calculates when your fertile days, including ovulation, are expected, and confirms the ovulation day. That means you can skip expensive ovulation tests. If you are trying to conceive, having intercourse in the three days before ovulation gives you the highest chance of conception — waiting until the ovulation day itself can already be too late.
A clearer way to understand your cycle
Natural Family Planning begins with understanding your own body. Daysy helps make that process easier through daily measurement, practical guidance, app support, and a hormone-free approach to fertility awareness.
Hormone-free. App-supported. Built with a precise sensor and a smart internal algorithm. Designed to help women understand fertile and non-fertile days more clearly.
Disclaimer. Daysy is a hormone-free fertility tracker designed to support cycle awareness and Natural Family Planning. It is not a contraceptive, and barrier methods such as condoms should be used on fertile days when avoiding pregnancy.