How accurate are ovulation calculators?

Written by: Dr. Amy Beckley, PhD, Founder and Inventor of the Proov test the first and only FDA-cleared test to confirm successful ovulation at home.

Written on 1/4/21

When trying to conceive, it is essential to track your cycle so that you can accurately time intercourse around ovulation. After all, without sperm and egg, conception is not possible!

Keep reading to learn more about ovulation calculators, how they work, and how to get pregnant faster.

What is an ovulation calculator and how does it work?

An ovulation calculator is an online tool that uses the first day of your period and the average length of your cycle to determine when you’re most likely to ovulate. This is vital information for women who are trying to conceive.

This is because after ovulation an egg is viable for 12 to 24 hours, which is a very short window of time. However, sperm can survive in a woman’s fallopian tubes for up to 5 days. This is referred to as your fertile window and research shows that pregnancy rates are higher when intercourse takes place the few days before and the day of the ovulation.

Ovulation calculators use the information you provide to predict your ovulation date, allowing you to time intercourse during the five or so days leading up to it. While this seems like a great tool, ovulation calculators may not be as accurate as they seem.

how accurate are ovulation calculators

Ovulation calculators use the first day of your period and the average length of your cycle to determine when you’re most likely to ovulate.

How accurate are ovulation calculators?

Ovulation calculators can be accurate, given your cycles are regular and you actually do ovulate every month without fail. This means that your cycle lasts a consistent amount of days cycle to cycle and you never experience anovulatory cycles.

The main problem with ovulation calculators is that they calculate your ovulation date based solely on the information you feed them and their results are just an average. Since a woman’s cycle can vary drastically month to month, cycle length and ovulation day are also subject to change. In fact, studies show that ovulation calculators are only accurate about 20% of the time.

This is because the hormones that trigger ovulation can also fluctuate month by month. If follicle-stimulating hormone (FSH), for example, rises and starts recruiting follicles earlier than normal, you may ovulate earlier than expected. Ovulation calculators have no way of telling what exactly is going on inside your body.

Is there a better way to calculate ovulation?

Thankfully, yes! You can still use an ovulation calculator as a general guideline, but there are plenty other, more accurate methods for predicting when ovulation is going to occur.

Ovulation (LH) tests

Ovulation tests — or luteinizing hormone (LH) tests — are by far the most reliable method for predicting ovulation. LH is the hormone that surges to trigger the follicle to release an egg about 24-36 hours before ovulation is going to occur. By measuring the presence of LH in your urine before ovulation, you can detect the LH surge that will begin the process of ovulation.

You can begin testing with LH tests once your period is over, although we don’t recommend beginning to test with Proov LH Tests until 18 days before your next expected period. As you near your day of suspected ovulation (about midway through your cycle), you may want to test LH twice a day, as LH surges can be short and easy to miss.

  • Pros: Easy to use and interpret, available over the counter, convenient as you only need to test for a few days.
  • Cons: May be inaccurate for women with PCOS who can have high levels of LH throughout their cycle, or for women approaching menopause whose LH levels may be elevated.

how accurate are ovulation calculators

We don’t recommend beginning to test with Proov LH tests until 18 days before your next expected period.

Basal body temperature (BBT) tracking

Basal body temperature (BBT)  tracking predicts ovulation by measuring the subtle changes in your body’s lowest resting temperature that happen before and after ovulation occurs. Before ovulation, BBT will slightly dip then the day after ovulation it will rise and remain elevated for several days.

Tracking BBT is inexpensive — you only need a thermometer and a temperature chart. However, you do need to be consistent as BBT tracking requires daily monitoring. You will need to measure your temperature every morning before you get out of bed. You shouldn’t get out of bed before measuring your temperature, as this may cause your temperature to rise and make your chart inaccurate.

  • Pros: Easy to use, cheap, natural.
  • Cons: Perturbed sleep, illness, alcohol consumption, and smoking are known to affect accuracy. Even a warmer or colder sleeping environment can affect the accuracy of your temperature reading. You have to test every day religiously in order to get a complete picture of your cycle. Many women need several months of readings before they come to identify a monthly pattern indicating ovulation.

Cervical mucus monitoring

Cervical mucus monitoring is another well-known ovulation prediction method. As hormone levels fluctuate during different stages of your cycle, the consistency and appearance of your cervical mucus changes too.

During the majority of your cycle, cervical mucus is dry and sticky. As you approach ovulation your cervical mucus gets more abundant, wet, and stretchy, often looking like egg whites. Once you ovulate, the cervical mucus becomes dry and sticky again

  • Pros: Least expensive of all ovulation tracker methods, always at hand.
  • Cons: May be altered by certain medication, previous cervical surgery, douching, sexually transmitted diseases, or perimenopause. Tracking after intercourse may invalidate findings as cervical mucus and semen may have a similar consistency and aspect.

But predicting ovulation is only half of the equation...

It is extremely important to make the difference between predicting and confirming ovulation. The methods we reviewed above may anticipate your body is about to release an egg, but it is totally possible to have an LH surge, have a BBT shift, or observe fertile cervical mucus and not ovulate after all.

This is why confirming ovulation (and that ovulation was successful!) is equally as important as predicting when it’s going to occur. “Successful” ovulation refers to an ovulatory event in which an egg was released and PdG (progesterone metabolite levels remained adequately elevated for a long enough period of time during the luteal phase to allow for the best possible chance at conception.

How Proov can help you predict and confirm ovulation

Here at Proov, we are strong believers that knowledge is power and that having a complete ovulation picture can help you get pregnant faster. Instead of simply calculating ovulation based on two questions, the Proov Predict and Confirm kit provides you with hormone tests for predicting and confirming successful ovulation.

The Proov Predict and Confirm kit comes with 15 LH tests and 5 PdG tests, which is enough for one cycle of testing. The LH tests will help you identify your two most fertile days while the PdG tests will confirm that successful ovulation did, in fact, occur.

how accurate are ovulation calculators

The Proov Predict and Confirm kit comes with 15 LH tests and 5 PdG tests, which is enough for one cycle of testing.

Ovulation calculators can be a helpful tool if you have a consistent cycle, but they fall short in providing valuable information about ovulation and your cycle. 

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“Hormone balance plays a huge role in fertility, and understanding what’s going on with your hormones doesn’t have to be such a mystery.

It’s actually way easier than most people realize.” 

— Amy Beckley, Proov Founder