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How do I calculate ovulation?

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 2/1/21

As we’re sure you know by now, ovulation is key to getting pregnant! Knowing when you ovulate can help you get pregnant faster.

When does ovulation occur?

By now you may be thinking, Great! Ovulation occurs on cycle day 14 so I should start having intercourse a few days before. While this is a good starting point, it’s actually a common misconception that ovulation occurs exactly on day 14 in every woman.

If you have a regular 28-day cycle, ovulating on day 14 could very well hold true for you. However, every woman is different and not every woman has regular 28 days cycles.

So, to be more accurate, we like to say that ovulation occurs midway through your cycle, marking the transition between the follicular and luteal phases. The middle of your cycle may happen anytime between cycle days 10 and 16, sometimes earlier, sometimes later.

For example, as we age our FSH levels increase, meaning our body may start to recruit follicles earlier (sometimes even during the luteal phase of the previous cycle). This may result in early ovulation — sometimes as early as day 8 — which is not considered uncommon or abnormal, and can absolutely lead to a healthy pregnancy and live birth.

Given the fact that ovulation day fluctuates from woman to woman, and even from cycle to cycle for the same woman, it is essential to track your cycle in order to accurately predict your fertile window.

how do I calculate ovulation

To be more accurate, we like to say that ovulation occurs midway through your cycle, marking the transition between the follicular and luteal phases.

Why should I track ovulation?

First of all, you should track ovulation so that you make sure you actually ovulate, as it can be a sign of proper endocrine function for a woman of reproductive age (15-49 years old). The absence of ovulation (also called anovulation) may signal autoimmune, genetic, endocrine, or nutritional disorders.

Additionally, you may want to track ovulation so that you identify your fertile window and optimize your chances of pregnancy when you are trying to have a baby. Once released by the ovary, a mature egg is only viable and fertilizable for about 12 to 24 hours. On the other hand, healthy sperm may survive in your reproductive system for up to 5 days.

That means that your fertile window may open as early as 5 days before you actually ovulate and closes 24 hours post egg release, at the latest. Tracking your cycles and establishing a certain pattern is extremely useful so that you can properly time intercourse when you are trying to conceive. Luckily, we have numerous tools these days allowing us to do that!

How do I calculate ovulation?

Establishing a pattern in your cycles is essential to understand how your body functions. Ovulation calculators, charts, and calendars do just that: try to predict when you might ovulate, taking into account the usual length of your cycle.

Basically, ovulation calculators offer you information based on the data you feed them. Typically, this information includes average cycle length and the start date of your most recent period. If you don’t know your average cycle length, the calculator will assume your cycle length is 28 days. A 28-day cycle is considered average, since a normal cycle may last anywhere between 22 and 36 days.

With the average luteal phase of a 28-day cycle being 14 days long, the calculator will count 14 days backward from the 28th day, to determine the estimated ovulation day and the 5 day long fertile window before ovulation.

However, because ovulation calculators are based on averages, they have no way of knowing what’s actually going on inside your body. Maybe your FSH was higher one cycle, you have a tendency to ovulate earlier, or you didn’t ovulate at all.

Based on this, ovulation calculators often do not work well for women with irregular cycles or PCOS. All in all, they are not reliable when used as the only ovulation predictor tool.

how do I calculate ovulation

Ovulation calculators are not reliable when sued as the only ovulation predictor tool.

Are there more reliable methods for predicting ovulation?

Thankfully yes! Here are some of our favorites:

Cervical mucus monitoring

Cervical mucus monitoring is one of the oldest family planning techniques. As your hormones fluctuate and change throughout your cycle, they influence the aspect, amount, and consistency of your cervical mucus.

Right before ovulation, an increase in estrogen levels causes your cervical  mucus to be more abundant, with a consistency that often resembles egg-whites. Its role is to nourish and help transport the sperm through your cervix and into your uterus. This is the best time to have intercourse if you are trying to get pregnant.

  • Pros: Free, easy to use, and always at hand
  • Cons: Accuracy may be altered by cervical surgeries, medication, douching, intercourse, or premenopause

Basal body temperature (BBT) charting

BBT charting is another handy way of tracking your cycle. Your basal body temperature is your body’s lowest resting temperature. Your BBT rises post ovulation and stays elevated throughout the luteal phase. You only need a thermometer (with two decimal places), a temperature chart, and consistency, as you will have to test every morning before getting out of bed.

  • Pros: Cheap and natural
  • Cons: Results may be altered by alcohol consumption, smoking, illness, room temperature, and irregular sleep patterns, among others.

Ovulation (LH) tests

Ovulation tests are by far the most accurate ovulation predictor. Ovulation tests work by detecting a luteinizing hormone (LH) surge in your urine.

As your follicles grow and mature during the follicular phase, your estrogen levels go up. Once they reach a certain level, this sends the signal to your pituitary gland to release an LH surge which triggers the lead follicle to release the mature egg.

Proov LH tests accurately detect this surge to offer you important information about your estimated ovulation and two most fertile days. Usually, the egg is released 24 to 36 hours after a positive ovulation test.

  • PROS: Accurate, only need to be used over 4-5 days during the follicular period
  • CONS: Not always accurate for women with PCOS whose LH levels are usually elevated throughout the cycle; nor for premenopausal women who may experience high LH due to hormonal imbalance.

how do I calculate ovulation

Proov LH tests accurately detect an LH surge to offer you important information about your estimated ovulation and two most fertile days.

While ovulation calculators can help you better understand your cycle, there are more reliable methods for ovulation prediction. Using one or more of these methods will help you more accurately find your fertile window and time intercourse so that you can get pregnant faster!