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When are women most fertile?

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

When you’re trying to get pregnant, one of the most important things you can do is understand when you’re actually fertile. Despite what your high school sex ed teacher may have told you, you can’t get pregnant every day of your cycle. That’s because female fertility comes roughly opposite your period, and you’re actually only fertile about 6 days each cycle! 

Knowing this is one thing, though, and knowing what to do with it is another thing entirely! To increase your chances of pregnancy, you can find out when you’re fertile and time intercourse during the fertile window (the time you can actually get pregnant). 

So when are women most fertile, and how do you find out when your chances of conceiving are greatest? Read on – we’ve got some answers for you! 

When are women most fertile? 

To understand when women are most fertile, let’s talk about the structure of the menstrual cycle. Your cycle begins on the first day of your period (called cycle day 1). During this time, overall hormonal activity is low. 

A few days in, estrogen begins to rise. Estrogen does two main things: it builds up your uterine lining for a possible pregnancy, and it makes your cervical mucus more fluid and better for sperm transport. 

When estrogen rises, this signals the opening of the fertile window and time of high fertility. This is because sperm can now survive 3-5 days in cervical mucus, and because a few days after estrogen has started to rise, it triggers the next step in the cycle: ovulation! 

Luteinizing hormone (LH) surges on average, around days 13-18 of your cycle, and 12-36 hours after LH surges, an egg is released! This brings us to our next point: what is ovulation, anyway? 

What exactly is ovulation and why is it important? 

Ovulation is the term for when a mature egg is released from the ovary and moves into the fallopian tube to potentially be fertilized. Ovulation can only happen once per cycle, at the end of the fertile window. A typical, healthy female will ovulate regularly, although it’s possible you may have an “anovulatory cycle” (or a time between two periods where you don’t actually ovulate) every now and then. 

Ovulation is important for two reasons. The first is that you can’t conceive naturally without it! An egg has to be released in order for sperm to fertilize it and make a baby. 

The second is that ovulation is also an important sign of health! Regular, successful ovulation is a good indication that your hormones are balanced, and it’s also important to keep your hormones in balance. 

That’s because the second half of your cycle, the luteal phase, is also related to healthy ovulation. After ovulation, the ovary begins to release progesterone, which is important to maintain the uterine lining as well as maintain bone density and promote good sleep. 

When you produce sustained, elevated progesterone during the luteal phase, and specifically the implantation window (days 7-10 after ovulation), your uterus is primed to accept a fertilized embryo, and we call this successful ovulation!

On the flip side, if you aren’t ovulating successfully, this greatly increases chances of miscarriage as well as other issues caused by low progesterone.

How do I find my fertile window? 

Now that you know why ovulation is important, how do you find your fertile days? There are a few popular (and highly effective) methods, so let’s go over them! 

Ovulation Calculators

An ovulation calculator means using either a formula or a period tracking app to “calculate” when you’re likely to ovulate, based on past cycle data. If you have regular cycles, this may work pretty well for you much of the time. 

Ovulation calculators are pretty low maintenance, so they’re an easy option to start with. If you have irregular cycles (or even just a weird cycle every now and then, which is typical for everyone), they may not work very well. Studies do show that different ovulation calculators can give different results even for the same cycle, too, so definitely take these with a grain of salt if you’re going to use one! 

Adding ovulation tests alongside your period tracker is an easy way to increase your chances of pregnancy! Read on for more about those. 

Learn more about ovulation calculators and irregular cycles.

Learn more about using Proov with a period tracker.

Ovulation Tests

Now that you know that luteinizing hormone (LH) triggers ovulation, the science behind most ovulation tests is easy! Ovulation tests, sometimes called LH tests or Ovulation Predictor Kits/OPKs, test for the presence of LH in your urine to predict ovulation. When they are positive, it indicates you’ll most likely ovulate in the next 12-36 hours. This is the best time to try! 

Some test kits, like Proov Complete, may also detect an estrogen rise, helping you find the entire fertile window (not just the day before ovulation). 

Learn more about using Ovulation Predictor Kits.

Learn more about ovulating with negative LH tests.

Basal Body Temperature (BBT)

Basal body temperature (your temperature every morning before you get out of bed) is a popular way to track ovulation. After ovulation, when progesterone starts to rise, your body temperature rises and stays higher for the rest of your cycle. 

Unfortunately, while BBT is a great way to confirm that ovulation occurred, the timing of the temperature rise means that it isn’t actually a very good way to find your fertile window (except retrospectively). You can use the time of your temperature shift to estimate when you might be fertile next cycle, but similar to an ovulation calculator, there’s no guarantee that current cycles will be the same as past cycles. 

Learn more about confirming ovulation.

Cervical Mucus Monitoring

Finally, did you know that your body actually has a built-in way to tell you when your fertile days are? 

When estrogen begins to rise, it stimulates the cervix to produce fertile cervical mucus, which becomes clear and slippery like raw egg whites. You can easily track this, and your chances of conceiving are highest on days with the highest quality cervical fluid. You can use cervical mucus tracking on its own, or pair it with any of the other methods described above (as well as your favorite Proov tests)! 

Learn more about how to track cervical mucus

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