When Will I Ovulate?

For couples trying to conceive (TTC), knowing your menstrual cycle is extremely important. One of the important questions you might be asking is; “ When will I ovulate? ”. That’s where Natural Cycles comes in. The app will tell you exactly when you are most fertile and give you a very accurate prediction of when you will ovulate by analysing your temperature and cycle. So you can get under the sheets with your loved one when it’s a good time and get to know your body while you’re at it. 

Let’s start with the basics.

Ovulation day is when an egg is released from the ovary and is ready to be fertilised by a sperm. An egg lives for up to 24 hours- As sperm can survive inside of you for up to 5 days,  this creates a 6 day fertile window, which is the timeframe when a woman can get pregnant. However, the likelihood of conceiving is dramatically increased if you have intercourse in the three days leading up to and including ovulation. If a woman has sex on any of these three days, she has a 27-33% chance of becoming pregnant [REF: Wilcox, A.J. et al. NEJM (1995) 333:1517].

Kalendar view: red colours indicate how fertile you are, the darker the red the more fertile you are

A good first step to get to know your cycle and find your fertile period is to know how long it is on average.  Day one is the first day of the menstrual period and the last day is the day before the next period begins. A general rule is the longer your cycle is, the later your ovulation day will be. For instance, a cycle that is long with 33 days between periods with an average ovulation day of CD 21, which means my most fertile days are CD 19, 20 and 21. If you have shorter cycle, say 21 days between periods, ovulation is likely to happen on CD 7 and your highest chance of getting pregnant will be on CD 5, 6, and 7.

However, these days are never set, especially for us irregular ladies. Have you ever noticed your period coming earlier or later than usual? Or ever wondered why your pregnancy test is negative even though you have no period? Well, it’s because a woman’s follicular phase, the first half of your cycle before ovulation, is often variable – my follicular phase can vary up to 6 days! What this all means is that your ovulation day can differ from cycle to cycle, which is why it is good to keep track of your temeprature and cycle with Natural Cycles. With a clear rise in temperature and a positive ovulation test (optional), ovulation can be confirmed and your fertile window is mapped for your upcoming cycle, which are indicated by red days. TIP: It is important to measure as much as possible in the week leading up to ovulation to ensure that we capture any variations!


Another popular question women ask about their cycles is, “When will I have my period?” or “When should I take a pregnancy test?”

Let’s review the second half of the cycle: The Luteal Phase.

This is the infertile stage of your cycle and is pretty consistent (usually around 12 to 14 days). This means it is a useful menstrual cycle characteristic that can be used to determine when you are likely to get your period, which is approx. 2 weeks after ovulation. However, you should know that the length of the luteal phase can also be quite individual and can vary between 6 and 18 days, so you should never assume that your ovulation day was two weeks prior to this. Instead it is much safer to calculate ovulation with reliable fertility indicators, such as temperature and ovulation prediction kits (OPKs), like we do.

Know when your period is coming up

Once Natural Cycles has detected your ovulation day it can accurately determine when your next period is due so you can keep calm and carry on!

Period trackers, which are based on the rhythm method, assume you are regular. Their primary goal is to let you know approximately when you can expect your next period, which will be around the same time each month as they do not detect ovulation or variations from your data. However, Natural Cycles, gets to know and adapts to your cycle no matter what shape or size it is, calculating your unique ovulation day each cycle giving you an accurate idea of when your period will come (variations included) each month.

At the end of your Luteal Phase, when you get your period, your temperatures will drop down again and the app will let you know a new cycle begins!

When will I ovulate and get my period?



Pregnancy tracker – plan users

Women usually take a pregnancy test from the first day of their missed period but not many know that the earliest point a woman can take a test is after the egg has been implanted in the endometrium at around day 9. It is fairly easy to recognise when you are pregnant if you are regular and know when your period is due but as mentioned before, if you are not, your period date could vary according to the length of your follicular or luteal phase each cycle.

Natural Cycles is a great tool for women that are planning a pregnancy, as it can determine from your data whether or not you have become pregnant! At the end of your Luteal Phase, if you don’t get your period and your temperature remains high (above the cover line) – the app will recommend that you take a pregnancy test to confirm it’s true.




If this is the case and you are pregnant, your temperature data entry dots will turn blue on your cycles chart.

Chart view: If your temperature stays elevated at the end of your luteal phase it means you might be pregnant and should take a pregnancy test to confirm. Blue dots indicate that you are pregnant.

As part of fertility awareness week, our next blog post we will talk about how fertility tracking can help you understand your reproductive health. Ask yourself, does your period come too often or maybe it doesn’t come at all? Find out answers next week or if you want to know sooner please get in touch with support@naturalcycles.com or visit ask.naturalcycles.com

Yours naturally,

The Natural Cycles team


New beautified NaturalCycles website out!

Today is the most amazing Friday ever! It’s a beautiful spring day in Stockholm and we could have lunch outside in the sun for the first time here at SUP46. They have a nice really big courtyard just outside the office.

What of course makes the day even better is that the new, beautified NaturalCycles website is out and the new iOS app has been submitted for approval. The new website is not only much prettier, but it also allows you to try NaturalCycles Prevent of Plan for free for 3 months, or you can pay for a year and get a basal thermometer shipped home to you. Cool! Another amazing feature of the new website is that it’s available in 6 languages!

NaturalCycles website

Continue reading

Great business meeting!

This Tuesday, NaturalCycles had a business meeting just outside Stockholm, in Kista, with an exciting potential business partner.

We discussed with them how we could work together in different ways. It went really well and they seemed enthusiastic about our ideas and also our product.

business meeting

We will meet them again for a longer meeting, about half a day, when we will go through our methodology and scientific studies to show them exactly how the algorithm behind NaturalCycles works. They will bring their own experts who will challenge us. This will be a very crucial step, but it will also be fun and exciting. We are now working on converting our long and detailed scientific paper into a shorter one, excluding the details of the algorithm that we don’t want to disclose.

The very first cycle with NaturalCycles

We get a lot of questions about how many green days to expect in the beginning when using NaturalCycles, since NaturalCycles needs some data to get to know you and your body. Every woman is different, with different cycle characteristics and different body temperatures, so we cannot make any reliable assumptions about your body until you start entering your own data in your NaturalCycles account.

The number of green days a woman gets in the first ovulatory cycle depends a lot on those first data points. What cycle day did she start measuring at? Does she measure every day or does she skip a lot of days? How much is her temperature fluctuating? Which cycle day does she ovulate? Has she recently been on hormonal contraception and will this postpone ovulation? I’ve already written a separate blog entry concerning how much the pill affects your cycle, here:


NaturalCycles requires 6 low temperature values before looking for a rise due to ovulation. This means that if she ovulates around day 15, she needs to start measuring around day 10 at the latest. If she starts measuring after the temperature rise, then it is of course not possible for NaturalCycles to detect ovulation. Below is such an example, where she started measuring on day 21:

One could argue that most probably ovulation had happened there and NaturalCycles could give green days, but before the following menstruation, there is really no way of knowing whether ovulation has happened and if the temperature is high, or if ovulation is for some reason delayed and the rise is still to come. As safety comes first, these days should not be green!

Below you see another example of a user that started measuring her temperature on cycle day 11, ovulated on day 20 and then got green days on day 23. She also entered a first positive LH test (ovulation test) on day 20, which helps to get easier green days.

In some extreme scenarios, where the woman does not measure very often in combination with highly fluctuating temperatures, it can take up to two cycles to get the first post-ovulatory green days.

To summarize: on average, if a user starts measuring before ovulation, she gets 40.2% green days during her first cycle. So even though the number of green days in the first cycle varies greatly, depending on several factors, the users do on average get a significant amount of green days.

Will quitting the pill disrupt your cycle?

I get a lot of concerned questions from women who are coming off the pill, or other hormonal contraception, and starting to use NaturalCycles as a birth control. How much will the hormones affect my cycle? Will NaturalCycles be safe and take the pill into account? How many green days (no need for condom) will I get? For those who are not familiar with NaturalCycles, it is a natural contraception, which analyses your body temperature, and optionally ovulation test data, to determine when you are fertile (red days) and when you most definitely are not fertile (green days).

Contraceptive pill

How much will the hormones affect my cycle?

The cycles of many women, although they had been many years on hormones, just directly go back to normal. Some women are only mildly affected, like for instance myself. I had the Implanon (the hormonal implant in the arm) for 10 years and after taking it out, my first 2 cycles were 5 weeks long, then a few cycles were 4 weeks and then back to 3.5 weeks, which is normal for me. Some women are unfortunately highly affected. The worst case I saw was a woman who quit the pill last summer and started measuring for NaturalCycles. Her first cycle was 108 days and since the time between ovulation and the next menstruation usually stays the same for one woman, she ovulated on day 97. Her next cycle was a bit shorter; about two months, and the one after that about 6 weeks. Basically it took almost a year until her cycle was back to normal.

The research that has been carried out on the subject has different conclusions, much depending on who was financing and/or performing the studies (one should not forget that the pharmaceutical industry has a very strong lobbying business). One interesting fact that I read is that the hormonal treatment that affects the cycle the most is the combined oral pill, which contains both progesterone and estrogen. For women using the combined pill, 50% got severely affected for the following year after stopping the pill. This was clear from a study performed on women quitting the pill in order to get pregnant and the majority of women who had been taken the combined pill had more difficulties to get pregnant. The good news is that after a year of being free of hormones more than 90% of the women had gone back to having regular cycles.

One conclusion to draw from this is that it is important to quit the pill quite some time before one plans to get pregnant. Not only due to the decreased chances of falling pregnant, but also to give the body a break for a while. It’s clear that being on a constant dose of hormones, is very disruptive and unhealthy for the body. If this is followed directly by pregnancy, which is an even stronger dose with lots of hormones, it might be even more difficult to find a balance again after the pregnancy and breastfeeding is over.

Will NaturalCycles be safe and take the pill into account?

Yes, definitely. When you set up your personal account with NaturalCycles, we ask you if you’ve recently been on the pill, for how long and when you stopped. NaturalCycles will then be extra cautious with your cycle and it knows that it’s very likely that you’ll start off with longer cycles, due to delayed ovulation, which will get shorter and shorter with time. So there is no need to worry, just be patient and confident that your cycle will eventually go back to normal.


How many green days you will get of course greatly depends on how much your cycle is disruptive by the use of hormones. If your cycle directly goes back to being somewhat regular, then no problem, you will get a nice amount of green days. If your cycle is very disrupted and you almost never ovulate, then the green days will be few. In that case, on the other hand, it is still very useful to monitor your cycle and confirm that it is slowly improving with time. The woman I mentioned above, who had a very disturbed cycle after quitting the pill, only had 25% green days her first year using NaturalCycles. 25% is still better than nothing and it’s nice for a couple to not have to use condoms 100% of the time, which is the other option when quitting the pill.

Overall, it is a big decision to quit the pill and to change birth control, and there is no guarantee that your cycle and body will just continue as nothing happened if you have been taking hormones for years. It’s nevertheless important to give your body a chance and to try to take the healthier path for the future.

Elina on the beach at sunset