6 Ways to Predict Ovulation: From Calendars to OPKs

When it comes to fertility, knowledge is power. Knowing your exact day of ovulation can increase your odds of getting pregnant, but in order to do that you need to know how to predict ovulation.  Once an egg is released it has 12 to 24 hours to be fertilized, but sperm can live in the body for up to five days.  That’s why your fertile window is a range of days around ovulation where the chances of pregnancy are possible. It sounds simple, but our cycles vary and there are many different methods to predict ovulation. 

To understand the best ways to predict ovulation, let’s look at how ovulation occurs and some of the methods used to track and predict it. 

Can you predict ovulation?

Regardless of when you ovulate, your sex hormones follow a predictable path before ovulation. Estrogen usually rises in the three to five days leading to ovulation while luteinizing hormone (LH) also surges 24 to 36 hours before ovulation, peaking 10 to 12 hours prior to ovulation.

The changes in these two hormones cause ovulation – the start of your fertile window – and are one of the most accurate and consistent signs of ovulation to track.  The signs and symptoms of ovulation strongly vary among women, but there are a variety of methods practiced by women to predict ovulation.  

The best ways to predict ovulation

Ultimately, this answer depends on your personal goals. For women who are seriously trying to conceive or avoid pregnancy, we recommend hormone testing, which can adapt to personal cycle variability. Hormones are the primary cause of ovulation and if tracked correctly, can achieve similar accuracy as lab-grade tests.

If your goal is to log and monitor your period, the calendar method is easy to use, and it gives you a good countdown towards your next period so that you can prepare. The mucus and saliva methods are good for when you want to pay more attention to your body and can be helpful to use alongside hormone testing to track the correlation between your hormone changes and physical symptoms.

Calendar Method 

Without taking into account personal and inter-cycle variation, ovulation happens about 14 days before the onset of the next period. If using the calendar method of fertility tracking, you should start charting the length of your cycle and calculate the predicted date of ovulation from there.

Unfortunately, this is not always true because every woman and every cycle is different. It usually takes >1 year of continuous charting to understand the pattern of your cycle. Although this method is very simple in theory, it may not be the most accurate when you really want to get pregnant or avoid pregnancy naturally.

Basal Body Temperature (BBT) 

Basal body temperature (BBT) is your body temperature at rest and is measured first thing in the morning, usually before you get out of bed. BBT increases about 0.5°F about 12 hours after ovulation. The egg only lives up to 24 hours after it is released from the ovaries, but sperm can survive in a woman’s uterus for 4-5 days, depending on the woman’s mucus consistency.

Therefore, the fertile window starts about 4 days before BBT surges. Given this, by the time you track the temperature surge, it is already too late to predict the entire fertile window.

Another common problem with this method is that it is easily affected by environment and health status. Since 0.5°F is a rather small change, environmental temperature change such as weather fluctuations, physical exercise, illness, or even the presence of air conditioning or electrical blankets could affect your temperature and make BBT fluctuate more than 0.5°F.

Hormone Testing and OPKs 

Luteinizing hormone (LH) surges about 24 – 36 hours before ovulation. Physiologically, the LH hormone is the primary cause of ovulation. Estrogen increases about 1-3 days before the LH surge and testing LH and Estrogen combined gives women their full fertile window. 

Aside from ultrasounds, which can only be done in the hospital, this is the most accurate method doctors use to predict ovulation. The challenge is that hormone levels significantly vary across different women and cycles. Ovulation prediction kits (OPK) determine ovulation based on a set hormone threshold, which can lead to false-positive and false-negative results.

Mira is the only home tracking device that tracks your actual hormone concentration at home. Using cloud-based AI, Mira learns your cycle variability through quantitative hormone tracking. Mira’s ovulation prediction is based on your personal situation, not the population average. Mira tells you how fertile you are, instead of giving you a binary “smiley or no smiley face” answer. This helps you prepare and understand your body more accurately.

Tracking Cervical Mucus Changes 

Another common method for tracking ovulation is noting changes in cervical mucus. As ovulation approaches your cervical mucus changes from thick to thin and almost an egg-white consistency. Every woman’s cervical mucus is unique so you need to get to know your own pattern in order to accurately track changes over time.

Monitoring Saliva 

This method of ovulation tracking includes looking at a sample of your saliva under a microscope. As you approach ovulation your estrogen levels increase which coincides with an increase in sodium levels. As your sodium levels go up, you can notice crystallization or ferning in your saliva. During this time if you look at a sample of your saliva under a microscope you will notice a pattern similar to a fern leaf which lets you know that ovulation is approaching.

Tracking Changes in Vagina Electrolytes 

Similar to the saliva crystallization method, the vaginal electrolyte method tracks changes in minerals in body fluids. This method requires a special monitor that registers electrolyte changes in cervical mucus throughout your cycle.

Unlike hormone testing, these last three methods are your body’s responses to estrogen hormone changes, which means that they are secondary indicators that might be affected by other physiological factors. These methods help you become more aware of your own body but can be easily affected by sex, food, illness, and other factors. Therefore, they may not yield the best prediction results as the primary ovulation tracking method, but they can be helpful additions to understanding your body when used together with hormone testing.

About ovulation

Ovulation occurs when an egg is released during menstruation. After release, the egg travels down the fallopian tube. It can either be fertilized by sperm or if no fertilization occurs, it causes your next period in a couple of weeks. For healthy women, ovulation usually happens in the middle of their menstrual cycle. Women are born with all the eggs they have and only a small percentage of them could potentially lead to pregnancy.

As we’ve learned, ovulation is controlled by hormone releases, which are managed by a part of the brain called the hypothalamus. It instructs the pituitary gland to secrete follicle-stimulating hormone (FSH) and luteinizing hormone (LH). The hormones also trigger certain changes to the body such as mucus properties, electrolytes inside the vaginal fluid, and saliva crystallization. After ovulation occurs, basal body temperature increases by about 0.5°F.

When are you the most fertile? 

You are most fertile on the day leading to ovulation and the day of ovulation.  These are known as peak fertility days and are when you are most likely to get pregnant.

How long does ovulation last? 

The process surrounding ovulation typically lasts 24-36 hours.  For most women this process typically occurs once per cycle, but in rare cases it is possible to ovulate multiple times in one cycle.  

Once the egg is released from an ovary, it can only survive for 12-24 hours if it’s not fertilized by a sperm.  If it’s not fertilized, the egg will disintegrate and is shed alongside the uterine lining during the menstrual period.  If the egg is fertilized by a sperm, it may result in a pregnancy.