New update in the Natural Cycles app: The Algorithm and the Predictions.

We are very proud to announce the improvements that our team has been focusing on over the past few months. We’re always striving to improve, and make the experience of using Natural Cycles simply  easier and better.  This time the focus has been on the algorithm and the new look of the predictions.

An optimised algorithm

Thanks to all your amazing data, the algorithm has now been updated and optimised to find ovulation with 10% higher precision.  If you are using Natural Cycles to prevent pregnancy this means that you could get more green days. If you are using Natural Cycles to plan a pregnancy, this means your fertile window will be more accurately pinpointed.

Smarter and clearer predictions

The predictions in both daily and the calendar view will have a new look.  (See below.) As you know predictions are only a prognosis for upcoming days, and might change as you add data. Therefore, they will now be visually different from past days and the current day, and will be shown in a grey color with a smaller circle that shows the prediction.

Another thing that will be new is the number of predicted cycles. In the calendar view you will see five predicted cycles, regardless of your cycle regularity. Smart, right?

As you might know, the predictions will get better the more you use Natural Cycles, and the more data it has.  

A smarter view of history

A lot of Cyclers have used Natural Cycles to prevent pregnancy, then switched to plan a pregnancy, or the other way around. Now, you will be able to see this visually in the graph, monthly and history view. This is a great way to track when you’ve switched to which plan.


Hope you’re excited as us about these upcoming changes. Any thoughts or feedback? Please comment below!

Your Natural Cycles Team

Upcoming changes to the Natural Cycles app

At Natural Cycles we are constantly working on improving the app so you can get the very most out of your experience with us. Within the upcoming months, we will be making some changes to the core functionality of the app, so we wanted to give all of our lovely Cyclers a heads up and also gather some feedback. With these changes we want to make the app even more clear and easy to use.

With Natural Cycles you should skip measuring when you feel sick, hungover or have slept more or less than usual. This is so you can get the best green day results.

Up until now you could also alternatively press the button ‘Don’t count this measurement’ when adding your temperature. This button will now be replaced by two buttons that mark your temperature as ‘Normal’ or ‘Deviating’. The functionality remains rather similar, let us explain…

What is a deviating temperature?

Certain factors can affect your temperature such as sickness, alcohol and lack of sleep. From now on we will be indicating this as a  ‘Deviating Temperature’, as it can skew your data and will cause you to have more red days – and you don’t want that right?

So if you have any of these symptoms, and still wish to save your temperature in the app – you should always manually mark it as a ‘deviating’ temperature. The app will also automatically detect very high deviations and you will notice this as the temperature will have a strikethrough.

A ‘Deviating’ temperature is not taken into account by the algorithm behind the Natural Cycles app to calculate your green or red day. So the more normal temperatures you enter the better your green day results are likely to be.

Skip today

Alternatively, you can now actively skip measuring your temperature by clicking ‘Skip today’ at the bottom of the add data page. You can also actively skip measuring if you forgot to measure in the morning and check the app later in the day.

This is great if you want to keep up the habit of checking the app in the morning and to keep track of how much you are measuring.

In your history and monthly view you will now exactly see when you have chosen to skip measuring so you have a better overview of your data. You can only skip today.

Days adding data

We will also update the data taken into account for your statistic of ‘Days adding data’. This will now only take ‘Normal’ temperature measurements into account as it is the key indicator for Natural Cycles to work effectively. LH and notes are optional so adding these will not affect these statistics anymore.

Anything above 75% days of adding normal temperature is a great achievement.

You might also have noticed that we’ve added reminders to Natural Cycles which we are very excited about. You can check out our blogpost about the Natural Cycles Reminders feature and how to use it here.

Hope you all enjoy the new features and looking forward to your feedback, please drop us a comment below – we would love to hear what you think. 

Your Natural Cycles team


How does the Natural Cycles algorithm work?

Behind the Natural Cycles app lies an unique algorithm that calculates your green and red days. This is the brains behind the app that pinpoints and predicts your ovulation, and the days you are fertile. What you might be wondering is how does it know when you are fertile or not?

natural cycles algorithm


The algorithm works by identifying your fertile days. These six days are calculated by taking your ovulation day and the five days before, because of possible sperm survival, into account.

Every woman and every cycle is unique, so the algorithm will have to get to know your cycles before it can tell you when ovulation has occurred. That’s why you might have more ‘red’ fertile days in the app when you get started with Natural Cycles.


Your basal body temperature shifts after ovulation and becomes higher due to release of the hormone progesterone. So the algorithm takes your temperature measurements and optional LH tests into account when calculating and pinpointing your ovulation and most fertile days. The app will let you know what your average temperature values are in luteal vs follicular phase, how your temperature curves look and get an overview of your fertile days. The algorithm will also calculate your predictions for the months ahead, depending on how regular your cycles are.



The longer you use Natural Cycles, the better it gets to know you.  It takes your cycle irregularities into account, the variation of your cycles and ovulation day, temperature fluctuations, length of follicle and luteal phase. On average, it takes up to 3 cycles for the Natural Cycles algorithm to get to know your cycles and gives you more and more green days.

The longer you use Natural Cycles, the better it get’s to know you.  You can see your irregularities in your stats page.  

Want to explore the powerful knowledge that lies behind our algorithm’s calculations? Sign up today and get to know yourself and your body better.


NEW feature – Calibrate your basal thermometer in the Natural Cycles app

With the new feature in the app, you are able to calibrate your basal thermometer. Calibrating your thermometer means you are able to see if you are measuring correctly, and if your thermometer is working properly.

natural cycles_basal thermometer

This is how you can calibrate your thermometer:

  1. Go to your account in the app or on the website.
  2. In your profile you’ll see “Calibrate your thermometer” button.


Now measure three times in a row, and enter it in the app. You can calibrate anytime and as many times as you wish!


To calibrate you need to measure your temperature 3 times in a row and enter the values in the app. Here is step by step instructions with few tips and tricks:


  1. Always measure in the same place and the same way for best results!

    Put the thermometer under your tongue, and only then click on the start-button. The thermometer will show you different values every time you measure. This is normal, since our temperature shifts, and also the thermometer gets warmer every time you measure. This is why it’s important to measure on the same place in your mouth when measuring, not only for calibrating the thermometer, but also when measuring every morning
  2.  The results and what they mean.

    When you’re done, the app will tell you if the calibration succeeded or if something might be wrong with how you measure, or your thermometer. The result you might get is:

    Calibration succeeded:  then everything is perfect and you should just keep doing what you’re doing.Calibration uncertain:  When the result shows “calibration uncertain”, you should first re-do the procedure and try again, as the result was borderline. Make sure you follow the instructions and measure correctly and in the same way all the three times. The second time you calibrate after getting the uncertain result, you will either get success or fail.

    Calibration failed: When your temperature shifts more than 0.3° degrees Celsius (or 0.54 degrees Fahrenheit) between the measurements, something might be either wrong with how you measure or your thermometer might need to be replaced. It is important to detect such issues early on as you otherwise might get too high day-to-day temperature variations for Natural Cycles to be able to detect your ovulation.


Have you calibrated yet? Log in and do it today and please comment on this blog post or leave your feedback here. If you’re not a Cycler yet, sign up today for the 1 year offer and get a basal thermometer included in the price.




What does it take to become a Star Cycler?

Natural Cycles wouldn’t be where it is today without the support of our strong community of Cyclers. We are grateful to all women spreading the word about us everyday. That’s why we decided to add the achievement of becoming a Star Cycler in the app.

“What is a Star Cycler?”

A Star Cycler status is the highest level you can achieve within the app, you receive full access to Natural Cycles for life – free of charge. That’s pretty freaking awesome.

“So how do I become a Star Cycler?”

Firstly, you must be a Pro Cycler to become a Star Cycler, which means that you fully understand how the app works and have had quite some experience with using the app.

Secondly, you should help us spread the word and vision of Natural Cycles to other potential Cyclers out there by referring 10 friends to Natural Cycles, you will get an email with a link to share with friends once you are a Pro Cycler. So get chatting with your girlfriends and sharing on your social media channels ladies. 

See you at the top,

Your Natural Cycles Team


Upcoming changes to Natural Cycles


During the past year we have continuously added more features and content to the application but we are not done yet! While you are reading this, our product team is hard at work on new content in the app that we hope will excite you. The changes are targeted at both new and experienced Cyclers with the goal of making it easier for all to go from novice to pro as well as getting more useful content. Feel free to have your say on all the changes in the comments below.



The “Me page” becomes “Cycle Statistics” and gets a redesign
We know that many cyclers really appreciate that they can see the numbers behind their unique cycle on the “Me Page”. That is why we have put some extra love into redesigning the visuals as well as adding some more content. In the new version you will be able to compare all your data with the average for all Cyclers, access deeper information on how to interpret the data and see how well you are performing at entering measurements. All the data will be split into four tabs; the full cycle, the follicular phase, the luteal phase and the ovulation. There will also be a small version of the graph to go with the different phases of the cycle.

Another important improvement is that you will now get direct feedback on is your temperature fluctuations. We will rate your fluctuation as either “Excellent”, “Good”, “OK”, “Problematic” or “Too high”. If your rating is “Problematic” or “Too high” we will give advice on how to improve and what the reasons for this may be. Hopefully this will help you lower your temperature fluctuations, which will help us to faster find your ovulation.



Cycler level

Are you a newbie or a pro? Well soon you will find out! As a part of the new profile section and the progress you make we will give you a rank of “Newbie”, “Junior”, “Skilled”, “Pro” or “Star” (the exact name of the ranks are still being discussed so feel free to give us feedback on them). We hope that this feature will put focus on your own individual performance and act as a motivator.



Achievements are intended to guide and motivate new Cyclers as well as will give a hint on what to expect from using the app over time. The more achievements a Cycler has reached, the better both she and the app will have gotten to know her unique body and cycle. An achievement is reached by completing tasks within the app or when the app first recommend the Cycler to perform a certain task. Here are a few examples of the achievements that will be available:


  • Add your first temperature measurement.
  • Add five temperature measurements in one week, Monday to Sunday.
  • Add twenty temperature measurements in one calendar month.
  • The application has detected your ovulation for the fist time.
  • The application has recommended you to take a LH test for the first time.
  • Get over 50% green days in one cycle.


“My Profile” is the new “Settings”

With the addition of your Cycler level and achievements we are renaming the settings tab to “My profile”. This will be where you can find these new features, all your personal settings and manage your account. We will also make your renewal date and selected payment option more visible.



New navigation

To go with all the new content and changes listed above we will make some adjustments to the tab navigation of the app. We will introduce a new icon for the “Cycle Statistics” tab and the “Me” icon will replace the old one for settings as this tab becomes “My Profile”. We are also considering adding labels to the tab navigation. As always we would love your feedback and thoughts on these changes.




Brand new graph design and features

We hear you, Cyclers! We appreciate all the feedback we have received on the app! We’re happy to announce the release of the new (and improved!) graph. Read all about the exciting features, below!


Access the graph whenever you want!

To view the graph, turn your phone to landscape mode and the graph will appear! Just make sure that the portrait orientation lock is off and you’re good to go.


Lines between the temperature values


You’ll notice the new graph now has lines between the temperature values. This is to make it easier for you to see the (possibly) slight fluctuations in temperature.




 Scroll through one, three or nine cycles

You can now see one, three or nine cycles at the same time. Also you can click on the ‘previous’ button and see previous cycles, one at the time.



See an estimate of your next temperature graph!

Now, you can see an estimated forecast of how your next temperature curve might look. This is a great feature for those of you who just started measuring.



New safe sex icon and changed place of the icons 


Now there is an icon for safe sex too, so you will see it in your graph whenever you log a protected intercourse. Before, the icons for intercourses were seen below the temperature chart, but now they are above it. The reason why we switched places is because sometimes the low temperature values could be hidden by the icons, and now you can clearly see both.


Let us know your thoughts and keep the feedback coming. We are listening! Also thank you for all support!


The Natural Cycles Team

Why do I get more red days?

Cyclers that are tracking their fertility with Natural Cycles sometimes wonder about the amount of red days. If you just got started with Natural Cycles it’s normal to get more red days. Natural Cycles is getting to know your unique cycle and probably hasn’t detected your ovulation yet. It is highly individual how fast ovulation can be found but usually it takes 1-3 cycles of measuring and adding data. So be patient and keep measuring. The red days will decrease with each cycle as the app gathers more data on you.

What other reasons can give you more red days? Let’s find out below!


  • After hormonal contraceptives

Our data shows that those who have previously taken hormonal contraception and just started with Natural Cycles experience more red days in the beginning. This is because it can take a while before your body starts ovulating again and the first cycles are often highly irregular. Since the first ovulation can come early or late, without warning, you will receive red days until it happens. So keep measuring!

  • Fluctuating temperature

If your temperature fluctuates more than usual, the app could give you more red days since it becomes more difficult to detect ovulation. Make sure that you always measure as soon as you wake up, and skip measuring if you sleep more or less than usual (+-2 hours).  Also skip measuring if you drink alcohol and feel hungover when you wake up or if you’re ill. Read more about how and when to measure.

  • Irregular cycles or anovulatory cycles

Some women have more irregular cycles than others. In your cycles statistics you can find out how much your ovulation day varies, and how regular or irregular your cycles are. You can also see how often you experience cycles without ovulation.


It’s rare that ovulation occurs on exactly the same day every cycle but for some women it varies a bit more than a couple of days. This is especially common if you have recently given birth or were taking hormonal birth control. Irregular cycles will give you more red days since your ovulation might be delayed or as a precaution if your ovulation will occur earlier than usual.

Tips for Cyclers that experience more red days

What could help Natural Cycles isolate your fertile window and help you get more green days is testing for LH (luteinizing hormone). A surge in LH occurs two days before ovulation and marks your most fertile days. Natural Cycles will let you know when you can begin testing your LH levels. See what our reminders look like and please read more about how and why you should test for LH.

Please feel free to email us if you would like for us to take a look at your data and help you with your chart!


Natural Cycles Team

Top measuring questions

In order to get the most out of Natural Cycles, it is important to measure at the right time in the right way. We decided to summarize the top 3 questions that we received from you on this topic.



1. Sometimes I wake up in the middle of the night and have to go to the bathroom. Can I still measure in the morning?

We recommend at least 3-4 hours of sleep before measuring. So, if you visit the bathroom 5 or 6 hours before it’s time to measure then you can go back to sleep and measure as usual when you wake up.

If you instead tend to wake up 1 hour before your measuring time, then you can measure at that time, as we recommend measuring within +-2 hours of timeframe.


2. Can I measure 30 minutes after I wake up, but still in bed?

If you like to snooze (like some of us do) then we recommend measuring as soon as you wake up first time. This is because we want to capture the basal body temperature, and your body will ‘wake up’ the more you wait and change the temperature. So for correct results measure as soon as you wake up and then keep snoozing!


3. I have a baby, and wake up several times at night. How should I measure?

We know that it could be difficult to keep up with the measuring if you have a baby to take care of and need to wake up several times per night.
We recommend you to measure as often as possible,  and after the longest period of sleep. Should one night be much worse  than your ‘average night’ then we recommend to simply skip measuring in the morning. 

measure basalbody thermometer

Also, here is a friendly reminder of dos and don’ts when it comes to measuring:



  • Always measure first thing in the morning, before you get out of bed in the morning.
  • Always measure underneath your tongue so that the metal point sits at the root of it.
  • For the first 3 cycles, try to measure as often as possible.
  • For the 5 days before and after expected ovulation, try to measure every day.
  • Disable temperatures if they seem abnormally high due to being sick or a change in routine: Long sleep-ins, drinking heavily, late night, slept badly.

Do not:

  • Do not measure on sick or hungover days as this will give you more red days than necessary.
  • Do not measure once you’re up and out of bed as this reading will not be your resting temperature (BBT).


The Natural Cycles Team

The new ovulation pictogram

With the release of the 2.0 version of our app we made a lot of visual changes. The reasons for these are plentiful, one of them is that we want to be more educational. Our goal is that our cyclers will learn more about their body from using the application. This will become even more apparent in future releases but a very clear example is the design of the new ovulation pictogram.

The ovulation is the release of an egg from the ovaries, so the obvious symbol to represent this is an egg. But not any egg, the human egg. Let it be known that the human egg—or ovum—does not look anything like a chicken egg, nor a grain of rice. To make it simple, the ovum is and looks like a cell. A roundish shape, approximately 0.12 mm in diameter, consisting of—among other things—an outer membrane and a nucleus. This is what the new ovulation pictogram depicts. You can see a picture of a real ovum below along with our previous and new pictogram. Note that a pictogram is intended to work in black and white, in small sizes and to be clearly visible even if viewed at a distance.

We are hopeful that our new pictogram will remind and/or educate cyclers and their partners on what the ovum is. Even in its simplified appearance.