How to calculate your fertile days?

If you want to get pregnant (and even if you don't!), it is important to recognise your fertile days. In this blog, we discuss how to recognise your ovulation and which methods can help you do so.

Calculating your ovulation: 3 methods

There are several methods to know when you ovulate: the calendar method, the cervical mucus method and the basal body temperature method. The first method is useful to get an indication of your cycle, but is not precise enough. Still, we discuss it briefly, because it can be an interesting start without being too much of a hassle.

1: Using the calendar method

This method is simple, but not the most reliable. It is the old-fashioned the pen-and-paper method: mark the first day of your period each month on a calendar (or use an app). The number of days between the first day of your period and the start of the next one is the length of your menstrual cycle.

The length of your cycle can change every month, but should always be about the same. If you menstruate irregularly, this method does not work well.

Once you know when you menstruate, you can calculate approximately when you ovulate. Typically, ovulation occurs between 12 and 14 days after your period. The phase between ovulation and the start of your period (the luteal phase) always lasts around 14 days. This is due to the predictable process of the corpus luteum, which breaks down if fertilization doesn’t occur, causing progesterone levels to drop and leading to menstruation. This phase remains constant, while the days before ovulation (the follicular phase) can vary, affecting your overall cycle length.

Your fertile window includes the five days before ovulation, the day of ovulation itself, and the day after—about one week in total.

There are many apps like Clue or Flo (see a list of them here), which make the old-fashioned calendar method easy. Just remember that these apps only work on algorithms. They only take into account the length of your period and do not track other important signals (your basal temperature and cervical mucus, see below)

2: Using the cervical mucus method

Want to know exactly when you're ovulating? Keep an eye on your cervical mucus.

Throughout your cycle, hormone levels change, affecting the consistency and quantity of vaginal mucus (also called cervical mucus). By checking your mucus daily and noting its appearance, you can learn a lot about your fertility.

When you ovulate, the mucus becomes thick, wet, and slippery, resembling raw egg whites. If your cervical mucus looks like this, you’re in your most fertile phase—the best time to try for a pregnancy.

Try tracking your mucus for one cycle and see if you notice any patterns. It might be tricky at first, but over time, you'll learn to recognize the signs. You can read more about cervical mucus in our blog post here.

3: Using the basal body temperature method

This method is a bit more involved, but when combined with the cervical mucus method, it’s one of the most effective ways to track your fertile days.

Your basal body temperature (BBT) is your body’s temperature at rest. To track ovulation using this method, you need to take your temperature every morning before getting out of bed.

You need a basal body thermometer, which is a more sensitive version of a regular thermometer. It can measure your body temperature to a tenth of a degree. This is important because a woman’s basal body temperature goes up slightly when she ovulates! Before ovulation, a woman's BBT averages between 36.1°C and 36.4°C.  After ovulation, it rises to 36.4°C  to 37°C. So, if you are diligently tracking your basal body temperature, you will see a rise in your temperature leading up to ovulation. 

You can track your temperature every day on a regular piece of paper, or you can use an app like Natural Cycles. This is the app that Guud founder Morgane uses and it is the first fertility awareness app that comes with a basal thermometer. 

There are also all kinds of handy devices available nowadays such as the Oura ring and Whoop to keep track of your temperature. You can then link these to Natural Cycle, so you don't have to take your own temperature. The Oura Ring collects ‘temperature trend’ data while you sleep instead of one single measurement. Not BBT. The Natural Cycles algorithm then creates an ‘absolute value’ based on that temperature trend data, which is the measurement you’ll see in the Natural Cycles app.

After three months of tracking, you should have a pretty good idea of when you’re ovulating. 

One important thing to note is that this method is not great at predicting your ovulation when you’re trying to conceive. Once you’ve detected a rise in temperature, you’ve already ovulated. Instead, you use this method to monitor your overall cycle and fertile window. 

When to have sex when trying to get pregnant

We could talk about how wonderful daily sex is, but at Guud Woman, we understand that trying to conceive can sometimes feel less than sexy. The good news is that you're more likely to want sex during ovulation—Mother Nature’s way of helping us reproduce!

For the best chance of getting pregnant, have sex every day or every other day during the five days leading up to ovulation, the day of ovulation, and the day after. Some suggest having sex every other day to maintain good sperm quality, and continue for two days after the presumed ovulation.

There’s a lot of debate about the “right” positions for increasing your chances of conception, but science shows no specific position increases your odds. Also, be mindful of the type of lubricant you use—some can negatively affect sperm quality, so make sure it’s fertility-friendly.

Want to know more? Here’s how your cycle affects your sex drive. 

What is the most accurate way to track your cycle? 

The most accurate way to track your cycle is to use both the cervical mucus and basal temperature method. Have you heard of the  Sensiplan method? It’s a combination of body awareness and fertility monitoring. The basic idea is that when you are completely aware of the regular signs in your own body, in combination with your basal body temperature, cervical mucus, your bleeding pattern and other symptoms, you will be able to accurately plan for or avoid a pregnancy. 

You can find out more about Sensiplan here. 

P.S. Hopefully you found this blog valuable. But why are we sometimes so cautious with our choice of words? Because we want you to understand that there's no miracle pill that solves everything (unfortunately!). Taking supplements is a way to support your health, but there are other factors at play like genetics, sleep, exercise, and diet. Do you have questions about your specific situation? Chat with us - we're happy to assist you, completely without obligation!