When Is the Fertile Window?

JANE FLANAGAN / FERTILITY PREGNANCY

If you’re trying to get pregnant, knowing when you might be ovulating is important. Your most fertile days ("the fertile window") are the 5 days leading up to and including ovulation. The fertile window is when you’re most likely to conceive and have the greatest chance of getting pregnant. 

So, if you're trying to conceive, having sex during your fertile window gives you the best chance of ensuring the sperm is present when the egg is released so that you can successfully become pregnant.

But before we dive into the fertile window, let’s recap what happens when you ovulate.

Ovulation: What Is It?

In order to become pregnant, an immature egg (or oocyte) has to be fertilized by a single sperm. Ovulation is a process that occurs on approximately days 13 to 15 of a 28-day menstrual cycle, during which your ovary releases an oocyte from a follicle. The oocyte then travels to the fallopian tube and awaits fertilization with sperm.

Once ovulation happens, the oocyte can be fertilized. At this point, timing is of the essence. After ovulation, you have about 12–24 hours for fertilization to occur. However, it’s worth noting that sperm can live inside a female body for up to 5 days, so the window for sexual intercourse to result in pregnancy is longer than just a couple of days. 

If the egg isn’t fertilized within 12–24 hours of its release, it begins to disintegrate slowly and will eventually shed along with the uterine lining during menstruation (your next period), approximately 11–16 days later.

Signs That You’re Ovulating

Many women do not have a cycle length of exactly 28 days, so tracking your own menstrual cycle can help you understand on which days of your menstrual cycle that you ovulate. Here are some things to look out for to know if you’re nearing or in the ovulation phase:

  • Lower basal body temperature (this typically occurs just before ovulation begins): It averages between 97°F (36.1°C) and 97.5°F (36.4°C) before ovulation, according to Healthlink BC
  • Higher basal body temperature (occurs approximately 24 hours after the egg is released and lasts for many days): It ranges between 97.6°F (36.4°C) and 98.6°F (37°C) after ovulation, according to Healthlink BC
  • Cervical mucus that is wet and stretchy with an egg-white texture: You may be at your day of ovulation
  • Softening of the cervix: Sometimes known as having a short, high, open, and wet cervix (SHOW)  
  • Subtle cramping 
  • Light spotting
  • Increased libido (sex drive) 

Understanding Your Fertile Days

If you want to get pregnant or to learn more about when you're fertile, it really starts with understanding your entire menstrual cycle. Most women are acutely aware of their period (the first day of your period is day 1 of your cycle), but they may be less familiar with the other events.

The first day of your menstrual cycle is counted from when your period starts and ends at the beginning of your next period. The average cycle length is 28 days. Ovulation is a key event and it occurs on approximately day 14 of a 28-day menstrual cycle (the average length).

Your most fertile days (the fertile window) are the 3 days leading up to and including ovulation. This is when you're most likely to get pregnant. So, if you're trying to conceive, having sex during your fertile window gives you the best chance of getting pregnant (i.e., ensuring the egg is fertilized by sperm so pregnancy can occur).

The Typical Menstrual Cycle, Day by Day

Your period marks the first day (day 1) of your cycle. If you have a 28-day menstrual cycle and ovulate regularly, the below is an outline of potential levels of fertility throughout the menstrual cycle.

Days 1–7:

Menstruation (shedding of the uterine lining) = Very low level of fertility 

Days 8–9: 

Post-Menstruation = Low–medium level of fertility 

Days 10–12: 

Pre-Ovulation = Medium level of fertility

Days 13–15: 

Ovulation = Very high level of fertility 

Days 16–18:

Post-Ovulation = Medium–high level of fertility 

Days 19–28: 

Pre-Menstruation = Low level of fertility  

Age and Fertility

Of course, fertility, menstrual cycles, and reproductive health can be impacted by several factors. Lifestyle and health conditions are among the other factors that can impact fertility and likelihood of pregnancy; however, age is one of the biggest natural reasons fertility can be decreased.

Your odds of getting pregnant are highest in your 20s and 30s, as this is when women are technically the most fertile and have the highest quantity of quality eggs. After the age of 35, the chances of becoming pregnant begin to decline. And by the time a woman turns 40, her chances of getting pregnant decrease to 10%, per menstrual cycle.

How to Know When Your Fertile Window Occurs

Ovulation predictor kits can be a useful tool for those trying to conceive and wishing to identify the best time to try to get pregnant: The fertile window. You should start testing 3 days before your expected ovulation day.

An ovulation predictor kit identifies the luteinizing hormone (LH) surge that happens 24–36 hours before the ovulation period. It’s important to factor in that sperm can survive in a woman’s body up to 5 days, so if you have sex before you ovulate, there can still be some present to fertilize the egg.

Every Cycle Is Different

Every woman’s cycle is different. Some of us have regular periods, longer periods, shorter cycles, or irregular cycles, for example. So the timing of when a woman ovulates is not always the same.

So, if your average menstrual cycle length is 28 days and the beginning of your cycle is day 1 of your menstrual period, day 14 in your cycle is your day of ovulation. Your most fertile days—and your fertile window—are days 12, 13, and 14. These are the days pregnancy is most likely to occur and when you should start testing with an ovulation calculator or test.

And if your average cycle is 35 days, ovulation happens around day 21 and your most fertile days are days 19, 20, and 21. These are the days when you should start testing with an ovulation calculator or test in order to increase your chances of pregnancy.

Other Signs & Symptoms of Ovulation

Ovulation usually goes unnoticed in many. But, as mentioned above, there are some symptoms of ovulation that most women can learn to track or pay attention to in order to understand their fertile window.

Your Basal Body Temperature Falls

One of the most objective symptoms is that your basal body temperature drops a little bit just before your egg is released from your ovary. Then, 24 hours later, your basal temperature rises and stays up for several days. If you're trying to get pregnant, it's advisable to take your temperature to understand when you're ovulating and potentially fertile.

According to Healthlink BC, your basal body temperature averages between 36.1°C (97°F) and 36.4°C (97.5°F) before you ovulate. It averages 36.4°C (97.6°F) to 36.4°C (97.6°F) after you ovulate. 

Discharge Changes When You Ovulate

The changes in your cervical mucus over the course of your menstrual cycle also hold clues about when you might be ovulating and more likely to experience pregnancy.

If your cervical mucus is...

  • Dry or sticky: It’s unlikely you’re ovulating
  • Creamy cervical mucus: Ovulation may be coming
  • Wet or watery: Ovulation may start soon
  • Wet and stretchy (egg-white texture): You may be at your day of ovulation

Your Cervix Softens and Opens Up

As you approach your most fertile time, your cervix softens. This is sometimes known as having a short, high, open, and wet cervix (SHOW). 

For a step-by-step guide to checking your cervix position, visit this guide on Flo’s website

You May Experience Slight Twinge or Cramping

Mittelschmerz translates literally as “middle pain” and is the name for the slight twinge or cramp that some women experience when the follicle releases the egg on the day of ovulation during their menstrual cycle.

Some Light Spotting May Occur When You Ovulate

When the ovaries release the immature egg (or oocyte), a tiny follicle ruptures to allow it to be released. This can be a cause of spotting for a day or so.

For some women, spotting that occurs around the time of ovulation is light red or pink in color. This is because we also produce more cervical fluid around the time of ovulation and the blood gets mixed with that fluid, causing it to be a lighter shade.

Increased Libido or Sex Drive

The most well-known sign of ovulation is an increased sex drive. It’s important to know that this does not mean you’ll only want to have sex during ovulation. But it may definitely mean that you may experience an increased libido when ovulation occurs.

Conclusion

Learning about your fertile window and tracking when it occurs can be an important step if you’re planning to get pregnant. Ovulation tests and fertility monitors give you a good ability to predict ovulation and the best days to conceive. However, there are other symptoms that you should also monitor and track to understand your fertile window.

Not only will being aware of these give you increased familiarity with your own menstrual cycle, but it will also give you good information to discuss with your doctor if you have any issues becoming pregnant.

Written by Jane Flanagan — Updated on April 5, 2022.

We hope you found this post informative — but remember: we’re not doctors and this post is not medical advice! While all posts are fact-checked and well researched, we always recommend you chat with your doctor about any questions or concerns you might have regarding a medical condition. We’re here to support and educate, but never with the aim of disregarding professional medical advice you’ve been given. Phew, now that that’s out of the way, you can go on living unapologetically free.